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Background: Thyroid testing strategies vary across laboratories. First‐line combined thyroid stimulating hormone (TSH) and freeT4 (FT4) have historically been preferred by many laboratories as this detects individuals with undiagnosed central hypothyroidism who can be missed with a first‐line TSH‐only strategy. However, an up‐to‐date evaluation of the utility of this approach is lacking. Objectives: We investigated the clinical utility of first‐line TSH and FT4 in the detection of central hypothyroidism in current day practice. Design, Patients, and Measurements: The All‐Wales laboratory information system was queried to identify thyroid function tests in patients aged ≥16 years with decreased FT4 and inappropriate TSH (low‐FT4). The 1‐year incidence of low‐FT4 was determined using mid‐year population data. Clinical information of patients with low‐FT4 was reviewed to determine causes of low‐FT4 and the incidence of central hypothyroidism. Results: The incidence of low‐FT4 varied according to FT4 assay method (range: 98–301 cases/100,000 population/year). Fifteen new cases of central hypothyroidism were detected in two health boards, equivalent to 2 cases/100,000 population/year. Positive predictive value of low‐FT4 for central hypothyroidism was 2%–4%. In a cross‐section of primary care patients, low‐FT4 was detected in 0.5% of all thyroid tests with assay‐related differences in detection rates. Conclusions: Although low‐FT4 is a common laboratory finding, the incidence of central hypothyroidism remains rare. With the currently increased rates of thyroid testing and increased use of medications that decrease FT4, low‐FT4 has a much lower predictive value for central hypothyroidism than previously reported. Thyroid screening strategies will need to balance the yield from first line TSH and FT4 testing with the cost of investigating individuals with non‐pathological laboratory abnormalities. [ABSTRACT FROM AUTHOR]

Context The serum total cortisol response to the ACTH stimulation test is widely used to assess adrenocortical function but is affected by changes in cortisol-binding globulin (CBG) concentration. Salivary cortisol reflects free cortisol concentrations and may offer a reliable alternative. Objectives (1) To establish the salivary cortisol response to ACTH stimulation in healthy volunteers and patients with altered CBG concentrations; (2) to evaluate the performance of a lower reference limit (LRL) determined in healthy volunteers in patients with suspected hypoadrenalism (SH-patients). Design A 250 µg ACTH stimulation test was undertaken in 139 healthy volunteers, 24 women taking an estradiol-containing oral contraceptive pill (OCP-females), 10 patients with low serum protein concentration (LP-patients), and 30 SH-patients. Salivary cortisol was measured by liquid chromatography-tandem mass spectrometry. Mean and LRL of the 30-minute salivary cortisol response (mean—1.96 standard deviation) were derived from log-transformed concentrations. The LRL was applied as a diagnostic cut-off in SH-patients, with comparison to the serum response. Results Mean CBG concentrations (range) were 58 (42-81) mg/L, 64 (43-95) mg/L, 41 (28-60) mg/L, and 116 (84-159) mg/L in males, females, LP-patients, and OCP-females, respectively. The mean 30-minute salivary cortisol concentration was 19.3 (2.5th-97.5th percentile 10.3-36.2) nmol/L in healthy volunteers. Corresponding values were not different in OCP-females [19.7 (9.5-41.2) nmol/L; P =.59] or LP-patients [19.0 (7.7-46.9) nmol/L; P =.97]. Overall diagnostic agreement between salivary and serum responses in SH-patients was 79%. Conclusion Salivary cortisol response to ACTH stimulation offers a reliable alternative to serum and may be especially useful in conditions of altered CBG concentration. [ABSTRACT FROM AUTHOR]

The article presents a study on the validity of paediatric reference intervals for clinical use. The study evaluated the laboratory database of renal profiles of children patients of primary care and observed the sodium results, potassium, and creatinine concentrations of the patients. Result shows that sodium concentrations, creatinine, and potassium were lower for infants from 1-5 years of age. It suggests that the reference was too broad and more appropriate paediatric ranges are needed.