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Background: Development of the gonads during fetal life is complex and vital for adult reproductive health. Cell and animal studies have shown an alarming effect of mild analgesics on germ cells in both males and females. More than 50% of pregnant women use mild analgesics during pregnancy, which potentially could compromise the reproductive health of the next generation. Objectives: We present a research protocol designed to evaluate the effect of prenatal exposure to mild analgesics and endocrine‐disrupting chemicals on gonadal function in the offspring. Population: Healthy, singleton pregnant women and their partners. Design: The COPANA cohort is a prospective, observational pregnancy and birth cohort. Methods: Participants were enrolled during the first trimester of pregnancy. Information on the use of mild analgesics was collected retrospectively 3 months prior to pregnancy and prospectively every 2 weeks throughout the study. We collected extensive data on lifestyle and reproductive health. Biospecimens were collected in the first trimester (maternal and paternal urine‐ and blood samples), in the third trimester in conjunction with a study‐specific ultrasound scan (maternal urine sample), and approximately 3 months post‐partum during the infant minipuberty period (maternal and infant urine‐ and blood samples). A comprehensive evaluation of reproductive function in the infants during the minipuberty phase was performed, including an ultrasound scan of the testis or ovaries and uterus. Preliminary Results: In total, 685 pregnant women and their partners were included between March 2020 and January 2022. A total of 589 infants (287 males) and their parents completed the follow‐up during the minipuberty phase (December 2020—November 2022). Conclusions: The Copenhagen Analgesic Study holds the potential to provide novel and comprehensive insights into the impact of early and late prenatal exposure to mild analgesics and other endocrine‐disrupting chemicals on future reproductive function in the offspring. [ABSTRACT FROM AUTHOR]

Context Nonprogressive premature thelarche (PT) is a self-limiting variant of early puberty, while idiopathic central precocious puberty (ICPP) is a disorder that causes progressive development of secondary sexual characteristics and often requires treatment. The diagnostic differentiation between these conditions is important but can be challenging since they often both initially present clinically with isolated breast development. Objective To describe relevant clinical variables in a large cohort of girls referred for early puberty, and to evaluate clinical and biochemical parameters to distinguish between girls with ICPP and PT. Methods This retrospective study included 1361 girls referred with signs of early puberty to a single, tertiary center from 2009 to 2019. We evaluated clinical presentation, medical history, growth velocity, bone age, hormonal serum concentrations, and gonadotropin-releasing hormone (GnRH) test results. Results Central precocious puberty was diagnosed in 11% (ICPP: n = 143, organic CPP: n = 11) girls, whereas 8% (n = 91 girls) presented with PT. Receiver operating characteristic (ROC) analysis showed several biochemical and anthropometric markers as potential parameters to differentiate between ICPP and PT; however, none were individually adequate. Principal component analysis (PCA)–derived clinical and hormone profiles could predict girls with ICPP from girls with PT with a specificity of 90% and sensitivity of 84%, outperforming any single marker. Conclusion Differentiation of girls with ICPP and PT can be supported by individual clinical and biochemical parameters. However, dimension reduction of clinical and hormonal profiles by PCA improved the diagnostic value, which in the future may support the diagnostic process as a supplement to the GnRH test in evaluation of pubertal disorders. [ABSTRACT FROM AUTHOR]

Background: Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) may affect the male reproductive system as it uses angiotensin‐converting enzyme (ACE)2, which is expressed in testicular tissue, as an entry point into the cell. Few studies have evaluated the long‐term effects of mild coronavirus disease 2019 (COVID‐19) on testicular function, and insulin‐like factor 3 (INSL3) levels have not previously been assessed during acute SARS‐CoV‐2 infection. Objectives: The aim of the study was to assess the impact of acute SARS‐CoV‐2 infection on testicular function including INSL3 and the presence of SARS‐CoV‐2 RNA in semen in non‐hospitalised men with mild COVID‐19. Materials and methods: This longitudinal study included 36 non‐hospitalised SARS‐CoV‐2‐positive men (median age 29 years). Inclusion was within seven days following a positive SARS‐CoV‐2 reverse‐transcription polymerase chain reaction test. Reproductive hormone levels, semen parameters, and the presence of SARS‐CoV‐2 RNA in oropharyngeal and semen samples were assessed during acute SARS‐CoV‐2 infection (baseline) and at three‐ and six‐month follow‐up. Wilcoxon matched‐pair signed‐rank (two samples) test was used to assess time‐related alterations in reproductive hormone levels and semen parameters. Results: Lower plasma testosterone (T) (total and calculated free (c‐fT)) and higher luteinising hormone (LH) concentrations were observed during acute SARS‐CoV‐2 infection (baseline) compared to three‐ and six‐month follow‐up. Consequently, ratios of c‐fT/LH were lower at baseline compared to three‐ and six‐month follow‐up (p < 0.001 and p = 0.003, respectively). Concomitantly, lower INSL3 concentrations were observed at baseline compared to three‐month follow‐up (p = 0.01). The total number of motile spermatozoa was also lower at baseline compared to six‐month follow‐up (p = 0.02). The alterations were detected irrespective of whether the men had experienced SARS‐CoV‐2‐related fever episodes or not. No SARS‐CoV‐2 RNA was detected in semen at any time point. Discussion and conclusion: This study showed a reduction in testicular function, which was for the first time confirmed by INSL3, in men mildly affected by SARS‐CoV‐2 infection. The risk of transmission of SARS‐CoV‐2 RNA via semen seems to be low. Febrile episodes may impact testicular function, but a direct effect of SARS‐CoV‐2 cannot be excluded. [ABSTRACT FROM AUTHOR]

Context: Supraphysiological serum insulin-like growth factor-I (IGF-I) concentrations have been a matter of concern in children treated with GH because high IGF-I levels were associated with risk of later disease in former epidemiological studies. Objective: To determine whether a single IGF-I measurement reliably reflects lifetime IGF-I exposure we evaluated intraindividual longitudinal tracking of IGF-I and IGF-binding protein-3 (IGFBP-3) levels and we estimated cumulative lifetime exposure to IGF-I in healthy and GH-treated individuals. Methods: We included 6459 healthy participants (cross-sectional=5326; longitudinal=1133) aged 0-76 years (9963 serum samples) and 9 patients born small-for-gestational-age (SGA) with 238 serum samples during GH treatment. Intraindividual tracking of IGF-I and IGFBP-3 (SD score [SDS]) was determined by intraclass correlation coefficients (ICCs). Cumulative lifetime IGF-I exposure was estimated by area under the curve of the predicted SDS trajectory from 0 to 76 years. Results: For IGF-I (SDS), ICCs were 0.50 (95% CI, 0.47-0.53) for male and 0.53 (0.50-0.56) for female participants. Lifetime IGF-I exposure was significantly higher in female (mean 12 723±3691 SD) than in male participants (12 563±3393); P=0.02. In SGA children, treatment with GH increased the lifetime exposure to IGF-I from 9512±1889 to 11 271±1689, corresponding to an increase in lifetime IGF-I trajectory from -0.89 SD±0.57 to -0.35 SD±0.49. Conclusion: Because IGF-I and IGFBP-3 levels track throughout life, a single measurement reliably reflects lifetime exposure. GH therapy increased the lifetime exposure to IGF-I only slightly and it remained below the average lifetime exposure in the reference population. [ABSTRACT FROM AUTHOR]

Introduction: Breast tissue in infancy is a rather undescribed phenomenon. We aimed to describe the prevalence and progression of palpable breast tissue in healthy boys and girls aged 0-1 years and to evaluate clinical markers, individual serum hormone concentrations as well as combined hormone profiles as determinants of the persistence of breast tissue. Methods: In total, 233 term infants (119 boys, 114 girls) were included and followed from birth until 1 year of age in The COPENHAGEN Minipuberty Study (ClinicalTrials.gov #NTC02784184). Infants were followed up to six times with a clinical examination and serum sampling. Principal component analyses (PCAs) produced combined hormone profiles. Results: A total of 98% of all infants aged 0-1 year exhibited breast tissue at some point. 50% still had breast tissue present at 0.5-0.6 years in girls and 0.3- 0.4 years in boys (‘persistent’). At one year, more girls than boys had breast tissue present (p=0.010). Most clinical and hormonal markers did not differ in infants with/without persistent breast tissue. However, in those with persistent breast tissue, estradiol (first visit, girls, p=0.034), androstenedione, corticosterone, cortisol (first visit, boys, all p<0.050), length (first visit, boys, p=0.030), and testicular volume (0.3-0.4 years, p=0.040) were higher, while IGF-I (0.3-0.4, boys, p=0.033) was lower. In boys, a combined, PCA-derived hormone profile (first visit) was able to predict the persistence of breast tissue (area under the curve=83%) better than any single marker. Discussion: Palpable breast tissue in infancy is common in both sexes although it persists in significantly more girls than boys at one year of age. Data supports both the early origin of breast tissue (in utero- and early postnatal) as well as a role of endogenous hormone production in later development and maintenance. [ABSTRACT FROM AUTHOR]

Objective: Little is known about the ratio between luteinizing hormone (L H) and follicle-stimulating hormone (FSH) during infancy. This study aimed to evaluate serum and urinary LH/FSH as a marker of sex with age-specific cutoffs in healthy infants. Design: A prospective, longitudinal cohort study of healthy infants ag ed 0-1.2 years. Methods: In total, 236 healthy infants (122 boys and 114 girls) from The COPENHAGEN Minipuberty Study (ClinicalTrials. gov ID: NCT02784184), with 567 serum and 603 urine samples, wer e included. Measures of diagnostic accuracy, including sensitivity and specificity, were used to assess the a bility of LH/FSH to detect sex in healthy infants. Results: In both serum and urine, LH/FSH was highest in males with mini mal overlap between the sexes. In contrast to isolated LH and FSH concentrations, LH/FSH ratios in both serum and urine were excellent markers of sex from 0 to 1.2 years with median sensitivities and specificities ranging fr om 93 to 100% with correspondingly narrow 95% CIs. Conclusions: Serum and urinary LH/FSH ratios are excellent discriminators of sex in healthy infants during the entire first year of life. The clinical role and application of the rat io remain to be elucidated. [ABSTRACT FROM AUTHOR]

Background: The hypothalamic‐pituitary‐gonadal (HPG) axis governs sexual maturation and reproductive function in humans. In early postnatal life, it is transiently active during which circulating sex steroids reach adult levels. While this so‐called minipuberty represents a universal phenomenon in infants of both sexes, its role for early maturation and growth remains incompletely understood. Objectives: To provide normative data on auxology as well as serum and urinary hormone levels in healthy, full‐term infants throughout the first year of life and to investigate associations of postnatal HPG axis dynamics as well as hormonal, genetic and environmental exposures with early genital development and growth. Population: Healthy, Danish, full‐term, singleton newborns including their parents. Design: Single‐centre, prospective, observational longitudinal pregnancy and birth cohort. Methods: Newborns were followed with six repeated clinical examinations during a one‐year follow‐up period. An umbilical cord blood sample was drawn at birth. At each visit, infants underwent a clinical examination focusing on auxology and genital development. Further, blood (serum, plasma, DNA) and urine samples were collected at each visit. Mothers and fathers underwent a clinical examination and provided blood samples prior to and after birth. A subset of parents provided urine samples and breast milk samples. Pregnancy and obstetrical outcomes, and detailed parental questionnaires were compiled. Preliminary results: Between August 2016 and August 2018, 2481 women with singleton pregnancies were invited to participate of which 298, including their partners, were enrolled (12.0%). A total of 268 healthy, full‐term newborns born appropriate for gestational age (AGA) were included at birth, 233 newborns participated in the postnatal follow‐up period and 186 completed the one‐year follow‐up period (9.4% and 7.5%, respectively). Conclusion: The COPENHAGEN Minipuberty Study provides detailed, longitudinal data on early genital development and growth including hormonal and genetic profiles and environmental exposure in healthy infants including additional data in their parents. [ABSTRACT FROM AUTHOR]

Purpose: Principal component analysis (PCA) is a mathematical model which simplifies data into new, combined variables. Optimal treatment of pediatric congenital adrenal hyperplasia (CAH) remains a challenge and requires evaluation of all biochemical and clinical markers. The aim of this study was to introduce PCA methodology as a tool to optimize management in a cohort of pediatric and adolescent patients with CAH by including adrenal steroid measurements and clinical parameters. Methods: This retrospective, longitudinal cohort of 33 children and adolescents with CAH due to 21-hydroxylase deficiency included 406 follow-up observations. PCAs were applied to serum hormone concentrations and compared to treatment efficacy evaluated by clinical parameters. Results: We provide and describe the first PCA models with hormone parameters denoted in sex- and age-adjusted standard deviation (SD) scores to comprehensibly describe the combined 'endocrine profiles' of patients with classical and non-classical CAH, respectively. Endocrine profile scores were predictive markers of treatment efficacy for classical (AUC=92%; accuracy 95%; p=1.8e-06) and non-classical CAH (AUC=80%; accuracy 91%; p=0.004). A combined PCA demonstrated clustering of patients with classical and non-classical CAH by serum 17-hydroxyprogesterone (17-OHP) and dehydroepiandrosterone-sulphate (DHEAS) concentrations. Conclusion: As an example of the possibilities of PCA, endocrine profiles were successfully able to distinguish between patients with CAH according to treatment efficacy and to elucidate biochemical differences between classical and non-classical CAH. [ABSTRACT FROM AUTHOR]

Objective: Insulin-like factor 3 (INSL3) is produced in the testes and has been proposed as a circulating biomarker of Leydig cell capacity, but remains undescribed in 45,X/46,XY mosaicism. The aim was to examine serum concentrations and gonadal expression of INSL3 in 45,X/46,XY mosaicism. Methods: Retrospectively collected data from medical records, gonadal tissue samples, and prospectively analyzed serum samples from eighteen male patients with 45,X/46,XY mosaicism (one prepubertal, four testosterone-treated, 13 untreated) were included. Biochemical, clinical, and histological outcomes were evaluated according to serum INSL3 concentrations, quantified by LC-MS/MS methodology, and gonadal INSL3 immunohistochemical expression. Results: Serum INSL3 concentrations spanned from below to above the reference range. In untreated patients, the median serum INSL3 SD score was -0.80 (IQR: -1.65 to 0.55) and no significant difference was observed between INSL3 and testosterone. There was no clear association between serum INSL3 and External Genitalia Score at diagnosis, spontaneous puberty, or sperm concentration. INSL3 and CYP11A1 expression overlapped, except for less pronounced INSL3 expression in areas with severe Leydig cell hyperplasia. No other apparent links between INSL3 expression and histological outcomes were observed. Conclusions: In this pilot study, serum INSL3 concentrations ranged and seemed independent of other reproductive hormones and clinical features in males with 45,X/46,XY mosaicism. Discordant expression of INSL3 and CYP11A1 may explain low INSL3 and normal testosterone concentrations in some patients. Further studies are needed to elucidate the divergence between serum INSL3 and testosterone and the potential clinical use of INSL3. [ABSTRACT FROM AUTHOR]

Background: With the development of molecular high-throughput assays (i.e. next generation sequencing), the knowledge on the contribution of genetic and epigenetic alterations to the etiology of inherited endocrine disorders has massively expanded. However, the rapid implementation of these new molecular tools in the diagnostic settings makes the interpretation of diagnostic data increasingly complex.Main Body: This joint paper of the ENDO-ERN members aims to overview chances, challenges, limitations and relevance of comprehensive genetic diagnostic testing in rare endocrine conditions in order to achieve an early molecular diagnosis. This early diagnosis of a genetically based endocrine disorder contributes to a precise management and helps the patients and their families in their self-determined planning of life. Furthermore, the identification of a causative (epi)genetic alteration allows an accurate prognosis of recurrence risks for family planning as the basis of genetic counselling. Asymptomatic carriers of pathogenic variants can be identified, and prenatal testing might be offered, where appropriate.Conclusions: The decision on genetic testing in the diagnostic workup of endocrine disorders should be based on their appropriateness to reliably detect the disease-causing and -modifying mutation, their informational value, and cost-effectiveness. The future assessment of data from different omic approaches should be embedded in interdisciplinary discussions using all available clinical and molecular data. [ABSTRACT FROM AUTHOR]

Sperm concentration is an essential parameter in the diagnostic evaluation of men from infertile couples. It is usually determined by manual counting using a hemocytometer, and is therefore both laborious and subjective. We have earlier shown that a newly developed image cytometry (IC) method may be used to determine sperm concentration. Here we present a validation of the IC method by analysis of 4010 semen samples. There was high agreement between IC and manual counting at sperm concentrations above 3 mill/ml and in samples with concentrations above 12 mill/ml the two methods can be used interchangeable. However, we found substantial differences in samples below 3 mill/ml. We also assessed the accuracy of the two methods by repeated measurements of 248 samples, which revealed that IC measurements seemed more accurate. Moreover, based on ten samples counted by several operators the IC method had a lower coefficient of variation than the manual method (5% vs 10%), indicating a better precision of the IC method. In conclusion, measurement of sperm concentration by IC can be used at concentrations above 3 mill/ml and seems more accurate and precise than manual counting, making it an attractive option in the daily clinical practice. [ABSTRACT FROM AUTHOR]

Background: Accurate and selective assessment of testosterone requires use of a sensitive LC-MS/MS method, especially at low levels as those seen in young children. Methods: The present longitudinal study of 20 healthy children from the Copenhagen Puberty Study followed every 6 months for 5 years evaluates the longitudinal increase in serum testosterone before, during and after pubertal onset quantified by a newly developed LC-MS/MS method in comparison with immunoassay. Testosterone concentrations in serum samples (n = 177) were determined by LC-MS/MS (detection limit 0.1 nmol/l) and by immunoassay (detection limit 0.23 nmol/l). Results: Serum concentrations of testosterone increased gradually with age by both methods. However, serum testosterone was quantifiable in 9/10 girls prior to pubic hair development measured with LC-MS/MS, and in 2/10 girls measured with immunoassay. In boys, testosterone was quantifiable in 10/10 boys 1 year prior to pubic hair development measured with LC-MS/MS, and only in 1/10 boys measured with immunoassay. Serum testosterone levels were quantifiable 1.5 years (range 0.5-2.5) earlier using LC-MS/MS. Conclusion: Assessment of longitudinal circulating levels of serum testosterone using a selective LC-MS/MS method proved to be more sensitive in predicting early peripubertal changes in healthy children compared to levels determined by immunoassay. © 2014 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Introduction Fibroblast Growth Factor 21 (FGF21) is a novel metabolic factor with effect on glucose and lipid metabolism, and shown to be elevated in diseases related to metabolic syndrome. Due to the increasing frequency of metabolic syndrome in the pediatric population, and as FGF21 studies in children are limited, we investigated baseline serum levels of FGF21 in healthy children during an oral glucose tolerance test. Methods A total of 179 children and adolescents from the COPENHAGEN Puberty Study were included. An OGTT with glucose and insulin measurements, a dual energy X-ray absorptiometry (DXA) scan and a clinical examination including pubertal staging were done on all subjects. Serum levels of FGF21, adiponectin, and leptin were determined by immunoassays at baseline. Results The girls had significantly higher levels of FGF21 compared with boys (155 pg/mL vs. 105 pg/mL, P = 0.04). 38 children (21%) had levels below detection limit of assay. Baseline levels of FGF21 showed positive correlation with triglycerides, but no significant correlations were found between FGF21-concentration and body mass index (BMI), DXA-derived fat percentage, LDL- HDL- and non-HDL cholesterol, leptin or adiponectin levels, respectively. Neither was any correlation found between baseline FGF21-levels and the dynamic changes in glucose and insulin levels during the OGTT. Conclusion FGF21 is independent of adiposity in children, and the significant metabolic effect seems to be limited to pathological conditions associated with insulin resistance. The higher levels of triglycerides in the girls may explain the significantly higher levels of FGF21 in girls compared with boys. [ABSTRACT FROM AUTHOR]

Insulin-like factor 3 (INSL3) is a promising marker of Leydig cell function with potentially high clinical relevance. Limited data of INSL3 levels in relation to other reproductive hormones in healthy pubertal boys exist. In this study, we aimed to evaluate longitudinal serum changes in INSL3 compared with LH, FSH, testosterone, inhibin B, and anti-Müllerian hormone (AMH) during puberty in healthy boys. Ten boys were included from the longitudinal part of the COPENHAGEN Puberty Study. Pubertal evaluation, including testicular volume, was performed and blood samples were drawn every 6 months for 5 years. Serum concentrations of testosterone were determined by a newly developed LC-MS/MS method, and serum concentrations of INSL3, AMH, inhibin B, FSH, and LH respectively were determined by validated immunoassays. The results showed that serum INSL3 levels increased progressively with increasing age, pubertal onset, and testicular volume. In six of the ten boys, LH increased before the first observed increase in INSL3. In the remaining four boys, the increase in LH and INSL3 was observed at the same examination. The increases in serum concentrations of LH, testosterone, and INSL3 were not parallel or in ordered succession and varied interindividually. We demonstrated that INSL3 concentrations were tightly associated with pubertal onset and increasing testicular volume. However, the pubertal increases in LH, INSL3, and testosterone concentrations were not entirely parallel, suggesting that INSL3 and testosterone may be regulated differently. Thus, we speculate that INSL3 provides additional information on Leydig cell differentiation and function during puberty compared with traditional markers of testicular function. [ABSTRACT FROM AUTHOR]

Using measurements of circulating anti-Müllerian hormone (AMH) in diagnosing and managing reproductive disorders in pediatric patients requires thorough knowledge on normative values according to age and gender.We provide age- and sex-specific reference ranges for the Immunotech assay and conversion factors for theDSL andGeneration II assays.With this tool in hand, the pediatrician can use serum concentrations of AMH when determining the presence of testicular tissue in patients with bilaterally absent testes or more severe Disorders of Sex Development (DSD). Furthermore, AMH can be used as a marker of premature ovarian insufficiency (POI) in both Turner Syndrome patients and in girls with cancer after treatment with alkylating gonadotoxic agents. Lastly, its usefulness has been proposed in the diagnosis of polycystic ovarian syndrome (PCOS) and ovarian granulosa cell tumors and in the evaluation of patients with hypogonadotropic hypogonadism. [ABSTRACT FROM AUTHOR]

Objectives: This study tested whether genetic variation in the CETP gene is consistent with a protective effect of cholesteryl ester transfer protein (CETP) inhibition on risk of ischemic events and on total mortality, without the adverse effects reported for torcetrapib. Background: Torcetrapib, an inhibitor of CETP, increased risk of death and ischemic cardiovascular disease of those randomized to the drug, despite improving the lipid profile. Methods: The Copenhagen City Heart Study is a prospective cohort study of 10,261 individuals, aged 20 to 93 years, who were followed for up to 34 years (1976 to 2010). Of these, 2,087 developed ischemic heart disease, 1,064 developed ischemic cerebrovascular disease, and 3,807 died during follow-up. We selected 2 common genetic variants in CETP previously associated with reductions in CETP activity, thus mimicking the effect of pharmacological CETP inhibition. Results: In individuals carrying 4 versus 0 high-density lipoprotein cholesterol–increasing alleles, there was an increase in levels of high-density lipoprotein cholesterol of up to 14% (0.2 mmol/l), and concomitant decreases in triglycerides, low-density lipoprotein cholesterol, and non–high-density lipoprotein cholesterol of, respectively, 6% (0.1 mmol/l), 3% (0.1 mmol/l), and 4% (0.2 mmol/l) (p for trend 0.004 to <0.001). Corresponding hazard ratios were 0.76 (95% confidence interval [CI]: 0.68 to 0.85) for any ischemic vascular event, 0.74 (95% CI: 0.65 to 0.85) for ischemic heart disease, 0.65 (95% CI: 0.54 to 0.79) for myocardial infarction, 0.77 (95% CI: 0.65 to 0.93) for ischemic cerebrovascular disease, 0.71 (95% CI: 0.58 to 0.88) for ischemic stroke, and 0.88 (95% CI: 0.80 to 0.97) for total mortality. CETP genotypes did not associate with variation in markers of possible side effects previously reported for torcetrapib. Conclusions: Genetic CETP inhibition associates with reductions in risk of ischemic heart disease, myocardial infarction, ischemic cerebrovascular disease, and ischemic stroke, with a corresponding antiatherogenic lipid profile, and with increased longevity, without adverse effects. [Copyright &y& Elsevier]

Clinical proteomics aims to deliver cost-effective multiplexing of potentially hundreds of diagnostic proteins, including distinct protein isoforms. The analytical strategy known as targeted proteomics is particularly promising because it is compatible with robust mass spectrometry (MS)-platforms already implemented in many clinical laboratories for routine quantitation of small molecules (i.e. uHPLC coupled to triple-quadrupole MS). Progress in targeted proteomics of circulating insulin-like growth factor 1 (IGF-I) have provided valuable insights about tryptic peptides, transitions, internal standards and calibrants. The present challenge is to examine if targeted proteomics of IGF-I can truly measure up to the routine performance that must be expected from a clinical testing platform. [ABSTRACT FROM AUTHOR]

An isotope-dilution TurboFlow-LC-MS/MS method for simultaneous quantification of the ten steroid metabolites dehydroepiandrosterone sulfate (DHEAS), progesterone, 17α-hydroxyprogesterone (17-OHP), Δ4-androstenedione (Adione), corticosterone, 11-deoxycortisol, cortisol, cortisone, testosterone (T), and estrone 3-sulfate (E1-S) in serum was developed and validated. Limits of quantification, variability (inter- and intra-day), analytical range and linearity were all found to be acceptable for clinical use. Furthermore, sample stability was evaluated including the influence of freeze-thaw cycles and the effects of temperature and storage time. The method was applied to 391 serum samples from healthy, Danish boys 10–18 years old. The concentration ranges of the included steroid metabolites for this population are presented. Concentrations of DHEAS, 17-OHP, Adione and T in the 391 serum samples were furthermore compared to results obtained using an existing LC-MS/MS method in our laboratory. Excellent agreement was found between the methods. Furthermore, the improved sensitivity of the new method allowed for quantification of a number of samples found to be below the LOQs of the existing method. Thus, the two instruments and their associated methods were validated as possible back-ups for each other, which we consider an extremely important issue in high-throughput laboratories analyzing clinical samples on a regular basis. The ten analytes included can be analyzed simultaneously but it is also possible only to include some of these analytes for specific diagnostic purposes which make the new method an extremely useful tool in the clinical laboratory. [ABSTRACT FROM AUTHOR]

Adrenarche is characterized by steadily rising levels of adrenal androgen metabolites from 4–6 years of age. We recently described marked gender-specific differences in circulating ratios between selected adrenal androgen metabolites in a cross-sectional study. This may suggest gender differences in steroidogenic enzyme activities. We therefore aimed at verifying these findings in a prospective, longitudinal study of healthy boys and girls who were examined during pubertal transition. A longitudinal study of 20 healthy children from the COPENHAGEN Puberty Study, followed every 6 months for 5 years. Clinical examinations were conducted and serum concentrations of Androstenedione (Adione), 17-hydroxyprogesterone (17-OHP), testosterone (T), dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS) were quantified by a newly developed LC-MS/MS method. DHEA, DHEAS, Adione, 17-OHP and T increase with age. Boys had higher levels of DHEAS from 10.5 years of age, whereas girls had higher levels of Adione from 13 years of age compared to boys. Interestingly, we observed significantly higher ratios of DHEAS/DHEA (sulfotransferase activity) in boys before and after pubertal onset compared to girls, whereas Adione/17-OHP (CYP 17 activity) appeared to increase more in pubertal girls compared to boys. This suggests that adrenal steroidogenic enzyme activities show developmental as well as gender-specific changes in healthy children. [ABSTRACT FROM AUTHOR]

The influence of sex, age, pubertal development and oral contraceptives on dehydroepiandrosterone (DHEA), DHEA sulfate (DHEAS), 17α-hydroxyprogesterone (17-OHP), Δ4-androstenedione (Adione), testosterone (T), calculated free testosterone (fT), free androgen index (FAI) and selected ratios in 1798 serum samples from healthy children, adolescents and young adults was evaluated. Samples were analyzed by Turboflow-LC–MS/MS. Sex hormone-binding globulin was analyzed by immunoassay. All steroid metabolite concentrations were positively associated with age and pubertal development in both sexes and generally higher in males than in females except for Adione. The pubertal rise in T in males was more pronounced compared to females, reflecting contribution from the testes. Ratios between steroid metabolites varied and depended on sex and age. All ratios were lower during infancy compared to later in life. Use of oral contraceptives significantly lowered serum concentrations of all steroid metabolites, fT, FAI, the 17-OHP/Adione, the Adione/T and the DHEA/Adione ratios, but not the DHEA/DHEAS ratio. We provide reference ranges for DHEA, DHEAS, 17-OHP, Adione, T, fT, FAI and selected ratios in relation to sex, age and pubertal development. Use of oral contraceptives strongly influences adrenal steroidogenesis and should be considered when diagnosing and monitoring treatment of patients with disorders of sex development. [ABSTRACT FROM AUTHOR]

Parabens are added to personal care products as antimicrobial preservatives. They have been suggested to have endocrine disrupting abilities. Prenatal exposure to parabens has been associated with reproductive endpoints including reduced male anogenital distance (AGD, distance from anus to genitals), which is sensitive to prenatal anti-androgenic exposure. To study the associations between maternal paraben concentrations in second trimester urine and AGD and reproductive hormone concentrations at 3 months of age in offspring. Pregnant women from Odense, Denmark were included in early pregnancy from 2010 to 12, and their children are being followed up. Fasting spot urine samples from 536 pregnant women were analyzed for methylparaben (MeP), ethyl-paraben (EtP), iso-propylparaben (i-PrP), n-propylparaben (n-PrP), n-butylparaben (n-BuP) and benzylparaben (BzP) by liquid chromatography tandem mass spectrometry and thereafter osmolarity adjusted. Three months after expected date of birth, AGD was measured in 452 children, and serum concentrations of follicle stimulating hormone (FSH), luteinizing (LH), testosterone, dehydroepiandrosterone-sulphate (DHEAS), androstenedione and 17-hydroxyprogesterone (17-OHP) were measured in 198 children. Maternal paraben exposure was categorized into tertiles or below and above level of detection, and sex-stratified multiple linear regression analyses were performed with AGD or reproductive hormones as outcomes. Most pregnant women had low concentrations of parabens in urine, but 10% exceeded the threshold for adverse estrogenic effects. Higher maternal paraben exposure was associated with shorter AGD in male offspring and longer AGD in girls, although only significant for MeP in boys. In addition, FSH, LH, DHEAS, 17-OHP concentrations were lower in girls with high prenatal paraben exposure, whereas no consistent pattern was found in boys. The endocrine disrupting abilities of parabens may affect humans at vulnerable time periods during development, which may have long term impact on reproductive function. This is the first study to find these associations in girls and our findings need confirmation. Unlabelled Image • Parabens are antimicrobial preservatives and suggested to have endocrine disrupting abilities. • Among 536 Danish pregnant women paraben in urine were low, but 10.4% exceeded the threshold for adverse estrogenic effects. • Higher maternal paraben exposure was associated with shorter anogenital distance (AGD) in boys and longer AGD in girls. • Sex hormone concentrations were lower in girls with high prenatal paraben exposure. • Prabens may affect humans at vulnerable time periods during development. [ABSTRACT FROM AUTHOR]

In the context of severe coronavirus disease 2019 (COVID-19) illness, we examined endogenous glucocorticoid concentrations, steroidogenic enzyme activity, and their correlation with inflammation and patient outcomes. This observational study included 125 hospitalized COVID-19 patients and 101 healthy individuals as a reference group. We utilized LC-MS to assess serum concentrations of 11-deoxycortisol, cortisol, and cortisone, as well as activities of steroidogenic enzymes (11β-hydroxylase and 11β-hydroxysteroid-dehydrogenase type 1). Cox proportional hazards regression analysis and competing risk analysis were employed to analyze associations between glucocorticoid concentrations and outcomes, adjusting for relevant factors. In patients with COVID-19, cortisol concentrations were higher and cortisone concentrations were lower compared to the reference group, while 11-deoxycortisol concentrations were similar. Steroidogenic enzyme activity favored cortisol production. Correlations between glucocorticoid concentrations and inflammatory markers were low. A doubling in concentrations cortisol, was associated with increased 90-day mortality and mechanical ventilation (HR: 2.40 95% CI: (1.03-5.59) , P = 0.042 and HR: 3.83 (1.19-12.31), P = 0.024). A doubling in concentrations of 11-deoxycortisol was also associated to mortality (HR: 1.32 (1.05-1.67), P = 0.018), whereas concentrations of cortisone were associated with mechanical ventilation (HR: 5.09 (1.49-17.40), P = 0.009). In conclusion, serum concentrations of glucocorticoid metabolites were altered in patients hospitalized with severe COVID-19, and steroidogenic enzyme activity resulting in the conversion of cortisone to biologically active cortisol was preserved, thus not favoring critical-illness-related corticosteroid insufficiency at the enzymatic level. Glucocorticoid release did not counterbalance the hyperinflammatory state in patients with severe COVID-19. High serum concentrations of 11-deoxycortisol and cortisol were associated with 90-day mortality, and high serum concentrations of cortisol and cortisone were associated with mechanical ventilation.

Objective: To describe the natural history of inhibin B throughout life according to sex, age, and pubertal development., Methods: Based on serum samples from 2707 healthy controls aged 0 to 80 years, sex- and age-specific reference ranges of inhibin B concentrations were constructed. Concentrations were evaluated according to pubertal development and use of oral contraceptives (OCs). Also, measurements from 42 patients with Klinefelter syndrome were included., Results: In both sexes, inhibin B concentrations were high during minipuberty, decreased in childhood, and increased significantly from Tanner stages B1 to B3 (peak: B4) in females and from G1 to G3 (peak: G3) in males. Despite variations in menstruating females, inhibin B concentrations remained relatively constant after puberty, until becoming unmeasurable at menopause. Despite a modest decrease, the inhibin B concentration in males remained relatively high from puberty onwards. At any age, males had highest concentrations. Inhibin B standard deviation (SD) scores were lower in OC-users (median SD score = -0.88) than in non-users (SD score = 0.35), p < 0.001. In patients with Klinefelter syndrome, inhibin B concentrations spanned the reference range until around 15 years of age, where they decreased to subnormal or unmeasurable levels., Conclusion: Valuable sex- and age-specific reference data for inhibin B concentrations were provided. In OC-users, decreased concentrations of inhibin B underlined the ovaries as the only place of inhibin B production. In patients with Klinefelter syndrome, the decline in inhibin B concentrations at puberty underlined the shift in regulation of inhibin B production at pubertal onset., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com. See the journal About page for additional terms.)

Background: Endogenous sex steroids influence the pubertal growth spurt and adult height. However, the impact of puberty suppression and sex steroids on growth in transgender adolescents is sparsely studied., Aim: We investigated pubertal growth, serum IGF-I and IGFBP-3, and adult height of transgender adolescents receiving hormone therapy., Methods: Observational study of a national cohort (2016-2023) comprising 219 transgender adolescents <18 years of age. Treatment consisted of gonadotropin-releasing hormone agonist (GnRHa) combined with estradiol or testosterone (adjusted to serum concentrations between 0 and +2 standard deviations (SDs) corresponding to the gender identity)., Results: Adult height was within ±2 SD for sex assigned at birth.Most trans girls reached adult height within references of girls. For trans girls (bone age ≤15 years before treatment), a growth spurt was observed during estradiol therapy. IGF-I and height SDS declined during oral estradiol administration (-0.13 SDS per month, p=0.059, and -0.02 SDS, p=0.001, respectively). We observed significantly lower adult height compared to target height for trans girls (-2.7 cm, p=0.01), and significant differences between height SDS before treatment and at adult height (-0.35 SDS, p<0.001).Half of the trans boys remained short (<-2 SD) compared to references for boys, and most completed growth spurt before initiation of treatment. IGFBP-3 declined following testosterone treatment. There was a significant difference between height SDS before treatment and at adult height (-0.17 SDS, p<0.001)., Discussion and Conclusion: The minor reduction in adult height of trans girls after hormone treatment may be beneficial to some, whereas trans boys did not experience height gain., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society.)

Context: Nonprogressive premature thelarche (PT) is a self-limiting variant of early puberty, while idiopathic central precocious puberty (ICPP) is a disorder that causes progressive development of secondary sexual characteristics and often requires treatment. The diagnostic differentiation between these conditions is important but can be challenging since they often both initially present clinically with isolated breast development., Objective: To describe relevant clinical variables in a large cohort of girls referred for early puberty, and to evaluate clinical and biochemical parameters to distinguish between girls with ICPP and PT., Methods: This retrospective study included 1361 girls referred with signs of early puberty to a single, tertiary center from 2009 to 2019. We evaluated clinical presentation, medical history, growth velocity, bone age, hormonal serum concentrations, and gonadotropin-releasing hormone (GnRH) test results., Results: Central precocious puberty was diagnosed in 11% (ICPP: n = 143, organic CPP: n = 11) girls, whereas 8% (n = 91 girls) presented with PT. Receiver operating characteristic (ROC) analysis showed several biochemical and anthropometric markers as potential parameters to differentiate between ICPP and PT; however, none were individually adequate. Principal component analysis (PCA)-derived clinical and hormone profiles could predict girls with ICPP from girls with PT with a specificity of 90% and sensitivity of 84%, outperforming any single marker., Conclusion: Differentiation of girls with ICPP and PT can be supported by individual clinical and biochemical parameters. However, dimension reduction of clinical and hormonal profiles by PCA improved the diagnostic value, which in the future may support the diagnostic process as a supplement to the GnRH test in evaluation of pubertal disorders., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Congenital adrenal hyperplasia (CAH) is a recessive condition that affects the adrenal glands. Despite life-long replacement therapy with glucocorticoids and mineralocorticoids, adult patients with CAH often experience impaired gonadal function. In pubertal boys and in men with CAH, circulating testosterone is produced by the adrenal glands as well as the testicular, steroidogenic cells. In this European two-center study, we evaluated the function of Leydig and Sertoli cells in 61 boys and men with CAH, primarily due to 21-hydroxylase deficiency. Despite conventional hormone replacement therapy, our results indicated a significant reduction in serum concentrations of both Leydig cell-derived hormones (i.e. insulin-like factor 3 (INSL3) and testosterone) and Sertoli cell-derived hormones (i.e. inhibin B and anti-Müllerian hormone) in adult males with CAH. Serum concentrations of INSL3 were particularly reduced in those with testicular adrenal rest tumors. To our knowledge, this is the first study to evaluate circulating INSL3 as a candidate biomarker to monitor Leydig cell function in patients with CAH.

Adult patients with Klinefelter syndrome (KS) are characterized by a highly variable phenotype, including tall stature, obesity, and hypergonadotropic hypogonadism, as well as an increased risk of developing insulin resistance, metabolic syndrome, and osteoporosis. Most adults need testosterone replacement therapy (TRT), whereas the use of TRT during puberty has been debated. In this retrospective, observational study, reproductive hormones and whole-body dual-energy x-ray absorptiometry-derived body composition and bone mineral content were standardized to age-related standard deviation scores in 62 patients with KS aged 5.9-20.6 years. Serum concentrations of total testosterone and inhibin B were low, whereas luteinizing hormone and follicle-stimulating hormone were high in patients before TRT. Despite normal body mass index, body fat percentage and the ratio between android fat percentage and gynoid fat percentage were significantly higher in the entire group irrespective of treatment status. In patients evaluated before and during TRT, a tendency toward a more beneficial body composition with a significant reduction in the ratio between android fat percentage and gynoid fat percentage during TRT was found. Bone mineral content (BMC) did not differ from the reference, but BMC corrected for bone area was significantly lower when compared to the reference. This study confirms that patients with KS have an unfavorable body composition and an impaired bone mineral status already during childhood and adolescence. Systematic studies are needed to evaluate whether TRT during puberty will improve these parameters.

The ratio between luteinizing hormone (LH) and follicle-stimulating hormone (FSH) has previously been described as an excellent marker of sex in healthy infants. However, LH/FSH remains not fully described in patients with differences of sex development (DSD). The aim was therefore to describe LH/FSH in infants with DSD. This was a retrospective study of DSD patients, all aged 0-1.2 years. In total, 87 infants with DSD and at least one serum sample per infant were included. Longitudinal samples from single patients were included whenever possible. Serum LH/FSH ratios in these patients were plotted against recently published age-related and sex-dimorphic cutoffs. Overall, LH/FSH sometimes corresponded to assigned sex without any obvious pattern in terms of diagnoses. LH/FSH corresponded to the biological sex in all patients with Turner or Klinefelter syndrome. In patients with 46,XX or 46,XY DSD (except congenital adrenal hyperplasia (CAH)), the ratios did not correspond to the assigned sex in all cases and were interchangeably within the male and female range. In patients with CAH, the ratio corresponded to biological sex (based on sex chromosomes) in some cases but also ranged across the cutoffs. In the 15 patients with 45,X/46,XY mosaicism, the LH/FSH ratios corresponded to the assigned sex in all cases (12 were raised as males, 3 as females) and at all time points in cases with multiple sampling. While this study describes LH/FSH in infants with DSD, the exact clinical role of the ratio in the management of these patients remains to be further elucidated.

Context: The male hypothalamic-pituitary-gonadal (HPG) axis is transiently active during the first months of life with surging serum concentrations of reproductive hormones. This period, termed minipuberty, appears to be essential for priming testicular function. Despite the central role for male reproductive function, longitudinal data on HPG axis activation in infancy is sparse., Objective: To explore the dynamics of HPG hormone activity in healthy male infants, to assess the association of HPG axis activity and testicular volume, and to establish reference curves for serum levels of reproductive hormones., Design: Prospective, longitudinal birth cohort (the COPENHAGEN Minipuberty Study, 2016-2018, 1-year follow-up)., Setting: Population-based., Patients or Other Participants: Healthy, male, term, singleton newborns were followed from birth on with repeated clinical examinations including blood sampling during a 1-year follow-up. A total of 128 boys contributed to this study, while 119 participated in the postnatal follow-up., Main Outcome Measures: Serum reproductive hormone concentrations and testicular volume., Results: Reproductive hormone concentrations showed marked dynamics during the first 6 months of age. Gonadotropins, total testosterone, and insulin-like factor 3 peaked at around 1 month of age. Inhibin B, anti-Müllerian hormone, and testicular volume peaked at around 4 to 5 months. Correlations largely recapitulated typical HPG axis pathways but also differed significantly from adult men., Conclusions: We demonstrate a temporal dissociation of Leydig and Sertoli cell activity during male minipuberty and provide reference curves for reproductive hormones., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The hypothalamic-pituitary-thyroid hormone axis might be affected in COVID-19, but existing studies have shown varying results. It has been hypothesized that hyperinflammation, as reflected by the secretion of cytokines, might induce thyroid dysfunction among patients with COVID-19. We explored thyroid hormone involvement in the acute phase of symptomatic COVID-19 and its possible associations with cytokine levels and mortality risk. This was a single-center study of 116 consecutive patients hospitalized for moderate-to-severe COVID-19 disease. Serum concentrations of thyroid-stimulating hormone (TSH), free thyroxine (T4), and 45 cytokines/chemokines were measured in all patients within 3 days of admission. Data were extracted retrospectively through a manual review of health records. At admission, 95 (81.9%) were euthyroid; while 21 (18.1%) had biochemically thyroid dysfunction including subclinical thyrotoxicosis (n = 11), overt thyrotoxicosis (n = 2), hypothyroidism (n = 1), non-thyroidal illness (n = 2), and normal TSH but high free T4 (n = 5). TSH levels were inversely correlated with IL-8 (rs = -0.248), IL-10 (rs = -0.253), IL-15 (rs = -0.213), IP-10 (rs = -0.334), and GM-CSF (rs = -0.254). Moreover, IL-8 levels, IP-10, and GM-CSF were significantly higher in patients with serum TSH < 0.4 mIU/L. Lastly, a two-fold increment of IL-8 and IL-10 was associated with significantly higher odds of having TSH < 0.4 mIU/L (odds ratio 1.86 (1.11-3.10) and 1.78 (1.03-3.06)). Serum TSH was not associated with 30- or 90-day mortality. In conclusion, this study suggests that fluctuations of TSH levels in patients with COVID-19 may be influenced by circulating IL-8, IL-10, IL-15, IP-10, and GM-CSF as previously described in autoimmune thyroid diseases.

Objective: Non-palpable testes remain a diagnostic challenge, often involving exploratory laparoscopy. We evaluated the diagnostic value of a wide range of reproductive hormones in order to distinguish between bilateral cryptorchidism and bilateral anorchia., Design: In this retrospective study, we identified and included 36 boys with non-palpable testes (20 with cryptorchidism, 3 with congenital hypogonadotropic hypogonadism (CHH), and 13 with anorchia) at first examination during childhood., Methods: Information on karyotype, phenotype, surgical results from laparoscopy, and biochemistry was retrieved from patient files. We compared serum concentrations of AMH, inhibin B, FSH, LH, testosterone, estradiol, and hCG stimulation testing in cryptorchid and anorchid boys to serum concentrations in a large, age-matched control group. Receiver-operating characteristic curves were used to determine the cut-off values of each reproductive hormone as a predictor of the presence of functional testicular tissue., Results: Concentrations of AMH in 0-1 year olds: ≥155 pmol/L and >1-15 year olds: ≥19 pmol/L, inhibin B (≥22 pg/mL and ≥4 pg/mL), FSH (≤28.9 IU/L and ≤20.3 IU/L) and hCG-induced testosterone (>1-15 year olds: ≥2 nmol/L) were significantly sensitive and specific markers in predicting the presence of functional testicular tissue in boys with non-palpable testes. In infancy, anorchid infants had significantly elevated gonadotropin levels, while CHH had low levels., Conclusion: Our findings suggest that laparoscopy may not be necessary in all boys with non-palpable testes if reproductive hormones unequivocally confirm the presence of functional testicular tissue. However, proving the absence may still be a diagnostic challenge.

Background: The peptide hormone insulin-like factor 3 (INSL3) is a marker for Leydig cell function and the clinical use of serum INSL3 measurements has been suggested by several groups., Aim: (1) To establish a reference range for liquid chromatography-tandem mass spectrometry (LC-MS/MS) of serum INSL3 in healthy boys and men; and (2) to compare the associations of serum INSL3 and testosterone (T) to pubertal stage, lifestyle factors, diurnal variation, body composition, and human chorionic gonadotropin (hCG) stimulation., Results: In a reference range based on LC-MS/MS analysis of serum from 1073 boys and men, INSL3 increased from levels close to the detection limit (0.03 µg/L) in prepubertal boys to a maximum mean level of 1.3 µg/L (95% CI, 0.9-2.7) in young men (19-40 years of age) and decreased slightly in older men (0.1 µg/L per decade). Serum T, but not INSL3, was associated with body mass index or body fat percentage and with alcohol consumption. Smoking was positively associated with serum T, but negatively associated with INSL3. There were significant diurnal variations in both INSL3 and T in men (P < 0.001), but serum INSL3 varied substantially less, compared with serum T (± 11% vs ± 26%). Mean serum INSL3 increased after hCG stimulation, but less than T (+ 17% vs + 53%). In both healthy men and in patients suspected of testicular failure, baseline serum INSL3 was more closely associated to the hCG-induced increase in serum T than baseline T itself., Conclusion: Measurement of serum INSL3 by LC-MS/MS has promise as a marker of testicular disorders., (© Endocrine Society 2020. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Context: The lack of sensitive and robust analytical methods has hindered the reliable quantification of estrogen metabolites in subjects with low concentrations., Objective: To establish sex-specific reference ranges for estrone (E1) and estradiol (E2) throughout life and to evaluate sex-differences using the state-of-the-art liquid chromatography tandem mass spectrometry (LC-MS/MS) method for quantification of E1, E2, and estriol (E3)., Design: LC-MS/MS method development and construction of estrogen reference ranges., Settings: Population-based cross-sectional cohorts from the greater Copenhagen and Aarhus areas., Participants: Healthy participants aged 3 months to 61 years (n = 1838)., Results: An isotope diluted LC-MS/MS method was developed and validated for measurements of serum E1, E2, and E3. Limits of detections (LODs) were 3 pmol/L (E1), 4 pmol/L (E2), and 12 pmol/L (E3), respectively. This sensitive method made it possible to differentiate between male and female concentration levels of E1 and E2 in children. In girls, E2 levels ranged from

Context: The early activation of the hypothalamic-pituitary-gonadal axis during infancy can be used in the evaluation of infants suspected of disorders of sex development (DSD). However, few data exist on sex-specific reference ranges for these hormones during early life., Objective: To evaluate sex differences in reproductive hormone concentrations in serum from healthy infants to define sex-specific cutoff values and to apply these in infants with DSD., Design: A cross-sectional study., Setting: A tertiary center for pediatric endocrinology at the University Hospital of Copenhagen., Patients or Other Participants: Healthy infants (1840) and patients with DSD (27), aged 2 to 5 months., Main Outcome Measures: Serum concentrations of LH, FSH, testosterone (T), estradiol, sex hormone-binding globulin (SHBG), inhibin B, anti-Müllerian hormone (AMH), dehydroepiandrosterone (DHEA), DHEA sulfate (DHEAS), 17-hydroxyprogesterone (17-OHP), androstenedione, and LH/FSH ratio., Results: LH and FSH concentrations showed overlap between sexes, with LH being highest in boys and FSH being highest in girls. The LH/FSH ratio separated infant boys from girls with minimal overlap at a cutoff value of 0.32. Inhibin B and AMH concentrations were markedly higher in boys compared with girls, with minimal or no overlap. In infants with Klinefelter syndrome, 45,X/46,XY mosaicism and male phenotype, and Turner syndrome, the LH/FSH ratio matched the gender of rearing. However, infants with complete androgen insensitivity syndrome had LH/FSH ratios within the male range., Conclusions: Reference ranges for reproductive hormones and LH/FSH ratio during mini-puberty were established in this study. The classifiers that best separated sex in mini-puberty were AMH, LH/FSH ratio, and T. Use of the LH/FSH ratio may add valuable information in the workup of infants suspected of DSD.