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Asthma is the most common chronic respiratory disease, affecting both children and adults. It is an umbrella term, encompassing multiple phenotypes. Asthma phenotypes may also be identified as clusters of measurements from different dimensions of the disease, and are partly genetically determined. The mechanisms leading to the disease are complex and it is still a challenge to choose suitable biomarkers, which have become especially important with the introduction of biological asthma treatment. Asthma can be broadly divided into T2-high and T2-low molecular endotypes. Early-onset asthma is typical of allergic phenotype and has so far been the most extensively investigated. The prevalence of adult-onset asthma is increasing because of the ageing population. This asthma phenotype can be divided into two types considering the existence of eosinophilic inflammation. Various other asthma phenotypes, for instance, exercise-induced, and obesity or smoking-associated asthma, should be taken into account when evaluating the patient. Severe asthma,with the prevalence of 5-10% of all asthma patients, remains a clinical challenge. Various biomarkers are thus under investigation in the hope of helping researchers and clinicians in better disease evaluation since the individual approach and personalized medicine are imperative.

Introduction: Tuberculosis (TB) is an infectious disease from which people suffer even in the 21st Century. According to official data for Croatia, the number of cases in the last decade has been decreasing. Aim: Due to the triple reduction in incidence in the last ten years in Croatia, the purpose of this study is to investigate whether patient characteristics have been changed, along with their comorbidities. Material and Methods: This was a cross-sectional study where we treated 230 patients (62.1% male and 37.8% female) age 40-60 years with tuberculosis in 2003 and in 2013, we treated 70 patients (54.9% of men and 45% women). Tuberculosis was diagnosed by direct microscopy of sputum, catheter aspirate, tumor tissue, lymph node puncture, swab wound in 2003 and by direct microscopy of sputum samples, catheter aspirates and bronchial washing samples in 50% of cases in 2013. Results: In 2003, 95.2% of patients had pulmonary tuberculosis. Comorbidities were found in 63.8%. 51.3% were smokers, 36.5% were alcoholics, diabetes and chronic obstructive pulmonary disease (COPD) was found in 12.2% and tumors in 6.5%. After 10 years, 91.4% of patients had pulmonary tuberculosis. 90% of them had comorbidities - 14.2% of patients had diabetes mellitus, 10% were treated for malignancies, COPD was present in 8.5%. 31.4% were smokers, while alcoholism was found in 11.4%. Conclusion: After 10 years tuberculosis has changed its face in South-East Europe. TB occurs more often in the elderly population with comorbidities in 90% of cases (mostly diabetes mellitus, malignancies and COPD). Men are no longer a risk group because women are affected almost equally. Clinical awareness of the possibility of TB should be considered in patients with comorbidities, and active screening and prevention should be undertaken

BACKGROUND: The aim of this study was to determine the distribution of ABO and RhD blood group phenotypes in the general population in the Republic of Croatia and among hospitalized patients with severe COVID-19. MATERIALS AND METHODS: Data on ABO and RhD blood groups of all blood donors in Croatia (who donated blood during the period 2015–2020) and patients and pregnant women tested at the Croatian Institute of Transfusion Medicine during the 2-year period, 2019–2020, were obtained from the e-Delphyn blood bank information system. A total of 614,673 results were analyzed in this group. The other group consisted of 780 COVID-19 patients hospitalized with severe COVID-19. Data are presented as total number and percentages and a comparison of proportions test was performed. RESULTS: The most frequent ABO phenotype in the general population is A (38%), followed by O (37%), B (18%) and AB (7%). RhD positive individuals accounted for 81% of the general population and RhD negative for the other 19%. Among COVID-19 patients, phenotype A was the most frequent (42%), followed by phenotypes O (32%), B (17%) and AB (9%). Thus blood group A was significantly more common among COVID-19 patients than among the general population, whereas blood group O was significantly less frequent. DISCUSSION: This study provides the first official results of the distribution of ABO and RhD blood group phenotypes in the general population in Croatia. Moreover, this study confirms other researchers’ observations about the predominance of the A blood group phenotype among COVID-19 patients.

Aims Biologics have been proven efficacious for patients with severe asthma (SA). It is essential to diagnose such individuals correctly. This study was designed to survey pulmonologists to identify barriers to early diagnosis and subsequent appropriate use of biologics for SA in Croatia. Methods A pulmonologist group with expertise in SA developed the initial list of questions, with the final questionnaire created according to a 2-round Delphi method. The resulting survey consisted of 23 items consequently divided into 4 domains: 1) Pulmonologists’ demographics and professional experiences; 2) Concerns about asthma management; 3) Attitudes toward SA diagnosis; and 4) Beliefs and attitudes regarding the use of biologics in managing SA. The given answers represented the respondents’ estimates. Results Eighty-four surveys were analyzed, with pulmonologists observing that general practitioners often inaccurately diagnose asthma and treat acute exacerbations. Although specialist centers are capably and correctly equipped, the time to diagnose patients with SA is approximately 3.5 months, with initial use of biologics delayed an additional 2 months. The primary indications for prescribing biologics are conventional therapy with oral glucocorticoids (91.7%) and frequent acute exacerbations (82.1%). In addition to improper diagnosis (64.3%), many patients with SA do not receive the indicated biologics owing to strict administrative directives for reimbursement (70.2%) or limited hospital resources (57.1%). Limitations The limitations of this survey include the subjective nature of the collected data, the relatively small sample size, and the lack of the biologic efficacy evaluation. Conclusions Croatian pulmonologists observed that a significant number of patients with SA who are eligible for biologics are not prescribed them, largely because of an inaccurate and/or delayed diagnosis, a delayed referral to a specialist center, highly restrictive criteria for reimbursement, and/or institutional budgetary limitations.

Brain-derived neurotrophic factor (BDNF) and its tropomyosin-related kinase B (TrkB) receptor might contribute to normal lung functioning and immune responses, however, their role in asthma remains unclear. Plasma BDNF concentration, as well as BDNF and NTRK2 (TrkB gene) polymorphisms, were investigated in 120 asthma patients and 120 healthy individuals using enzyme-linked immunosorbent assay and polymerase chain reaction, respectively. The genotype and allele frequencies of BDNF Val66Met (rs6265) and NTRK2 rs1439050 polymorphisms did not differ between healthy individuals and asthma patients, nor between patients grouped according to severity or different asthma phenotypes. Although plasma BDNF concentrations were higher among healthy subjects carrying the BDNF Val66Met GG genotype compared to the A allele carriers, such differences were not detected in asthma patients, suggesting the influences of other factors. Plasma BDNF concentration was not affected by NTRK2 rs1439050 polymorphism. Asthma patients had higher plasma BDNF concentrations than control subjects, however, no differences were found between patients subdivided according to asthma severity, or Type-2, allergic, and eosinophilic asthma. Higher plasma BDNF levels were observed in asthma patients with aspirin sensitivity and aspirin-exacerbated respiratory disease. These results suggest that plasma BDNF may serve as a potential peripheral biomarker for asthma, particularly asthma with aspirin sensitivity.

During a two-year period (2001-2003), 464 patients were treated for tuberculosis at Jordanovac Department for Lung Diseases in Croatia. Besides pulmonary tuberculosis in 97.7% of patients, patients were also treated for tuberculous pleurisy (0.9%), tuberculous laryngitis (0.6%), tuberculous meningitis (0.2%), tuberculous pericarditis (0.2%) and urogenital tuberculosis (0.4%). Out of the total number of patients, 57.3% declared themselves to be active smokers (men were predominant and made up to 80.8%) and 20.9% to be active alcohol consumers. Both risk factors, i.e. smoking and alcohol consumption, were present in 15.1% of all patients. The most common comorbidities were diabetes mellitus (30.4%), cardiac diseases (11.2%) and chronic obstructive pulmonary disease (8.0%). Lung carcinoma was the most common malignant disease (n=51), with Mycobacterium tuberculosis isolated in 33% of them. Seventy-two of 464 (15.5%) patients had recurrences of tuberculosis. Of these, 30.5% had one of the risk factors (20.8% were smokers and 9.7% consumed alcohol), while 32.5% of patients had both risk factors. In conclusion, cigarette smoking was proved to be the most significant risk factor for development of pulmonary tuberculosis and its recurrence., Tijekom dvije godine (2001.-2003.) u Klinici za plućne bolesti “Jordanovac”, Zagreb, Hrvatska, od tuberkuloze je liječeno 464 bolesnika. Osim najčešće plućne tuberkuloze u 97,7% bolesnika, oboljeli su liječeni i od eksudativnog tuberkuloznog pleuritisa (0,9%), laringealne tuberkuloze (0,6%), tuberkuloznog meningitisa (0,2%), perikardijalne tuberkuloze (0,2%) te tuberkuloze koja je zahvatila urogenitalni sustav (0,4%). Od ukupnog broja bolesnika 57,3% ih se izjasnilo kao aktivni pušači (muškarci 80,8%), dok je 20,9% deklarirano kao aktivni konzumenti alkohola. Ukupno je 15,1% bolesnika imalo oba rizična čimbenika u anamnezi, tj. i aktivno pušenje cigareta i konzumaciju alkohola. Od komorbiditeta najčešća je bila šećerna bolest u 30,4% bolesnika, od srčanih bolesti bolovalo je 11,2% bolesnika, dok je kronična opstruktivna plućna bolest bila prisutna u 8% bolesnika. Karcinom pluća bio je najčešće zastupljen među malignim bolestima. Od ukupnog broja oboljelih od karcinoma pluća (51 bolesnik), Mycobacterium tuberculosis izolirali smo u 33% bolesnika. Recidivi tuberkuloze su zabilježeni u 72 (15,5%) bolesnika. Jedan rizični čimbenik imalo je 30,5% bolesnika: pušača je bilo 20,8%, dok je alkohol konzumiralo 9,7% bolesnika, a 32,5% bolesnika imali su oba rizična čimbenika. Zaključno, pušenje cigareta pokazalo se kao najznačajniji rizični čimbenik za razvoj plućne tuberkuloze, kao i za pojavu recidiva tuberkuloze.

Asthma is one of the most common chronic diseases in the world. Obesity is the most common comorbidity of asthma and is connected to incidence and course of the disease. Obesity is associated with non-allergic asthma phenotype, but this relation could be influenced by gender. The aim of our study was to determine the relationship between BMI and asthma and to explore possible gender differences.Study included 149 patients with asthma (examined group) and 153 healthy blood donors (control group). Data from the medical records of patients with asthma were used, and all included subjects had their BMI calculated using standard formula. Data were analyzed using descriptive statistics methods. Data with non-parametric distribution were analysed with Mann-Whitney U test and showed through medians with corresponding interquartile ranges. Statistical significance of BMI differences between non-allergic asthma, allergic asthma and control groups were analyzed by one-way analysis of variance - ANOVA. The results were interpreted at a significance level of P0.05.The comparison between median BMI values of two groups shows that examined group of patients with astma has significantly higher median BMI value in comparison with control group (P=0.035). Correlation was stronger for women than men (P=0.002 vs P=0.898). Incresed BMI of the examined group of patients with asthma was not asociated with non-allergic asthma (P=0.085). However, when stratified according to gender, there was a strong association of increased BMI with non-allergic asthma in women (P0.001).Patients with asthma in our study have higher BMI in comparison to healthy individuals, which contributes to hypothesis that BMI is a risk factor for development of asthma. We found that possible effect that BMI has on asthma is stronger in women, since there was a strong association between increased BMI and non-allergic asthma only in women.

Respiracijske alergije manifestiraju se na gornjim i donjim dišnim putovima, klinički kao alergijski rinitis i astma. Astma je četvrta bolest u svijetu, a Hrvatska pripada zemljama sa srednje visokom prevalencijom. Ona je heterogena bolest s brojnim fenotipovima, od kojih se neki dobro kontroliraju inhalacijskim kortikosteroidima, i ponašaju se benigno, dok se u drugih kontrola astme ne može postići niti kombinacijom steroida i dugodjelujućeg bronhodilatatora. Poseban fenotip astme predstavlja teška astma, na koju otpada oko 5% ukupnoga broja bolesnika s astmom. Termin teška ili refraktorna astma odnosi se na bolesnike koji imaju simptome bolesti usprkos prikladnoj terapiji i uz provjereno dobru suradljivost, primjeren inhaler i dobru tehniku inhaliranja.Teška se astma, prema preporuci radne skupine Američkoga torakalnog društva i Europskoga respiratornog društva, definira kao oblik bolesti kod koje je potrebno trajno liječenje, preporučeno za stupnjeve GINA-e 4 i 5, kako bi se spriječilo da bolest postane nekontrolirana, te, nadalje, astma koja ostaje nekontrolirana unatoč ovoj terapiji. Radi se o skupini bolesnika koja ima brojne dnevne i noćne tegobe, učestale egzacerbacije i hitne intervencije, nisku plućnu funkciju, bez normalizacije nalaza, a postoje i smrtni ishodi, usprkos redovitom korištenju svih lijekova za astmu s dobrom adherencijom i primjeni preventivnih mjera (prestanak pušenja, idealna tjelesna masa i smanjenje anksioznosti). Veliki napredak u liječenju i nova nada za tu grupu teških bolesnika s astmom predstavlja nova biološka terapija. Zahvaljujući razvoju imunologije, u praksu su uvedeni lijekovi koji blokiraju neki od dominantnih mehanizama u astmi, poput anti IL-5 mehanizma u eozinofilnoj astmi ili anti IgE mehanizma u alergijakoj astmi, koji zaustavljaju alergijsku upalnu kaskadu. Primjena bioloških lijekova u liječenju astme započela je uporabom omalizumaba. Omalizumab je humanizirano anti-IgE protutijelo, s odobrenim indikacijama za liječenje teške, perzistentne alergijske astme (u djece ≥ 6 godina starosti, adolescenata i odraslih), te kronične spontane urtikarije (u adolescenata i odraslih). Omalizumab veže slobodni IgE, te ga time smanjuje za više od 96% od početnih vrijednosti. Posljedično dolazi do smanjene ekspresije FcεRI receptora za IgE na mastocitima, bazofilima i dendritičkim stanicama, na koje bi se taj slobodni IgE vezao. Time se pri ponovnom doticaju s alergenom smanjuje mogućnost degranulacije tih stanica i dolazi do otpuštanja upalnih citokina, a samim time i simptoma i egzacerbacija astme. Omalizumab se pokazao učinkovitim u liječenju teške, perzistentne alergijske astme, uz dobro utvrđen i poznat sigurnosni profil; značajno je smanjio teške egzacerbacije astme, dnevne i noćne simptome astme, godišnji broj odlazaka na hitnu pomoć i hospitalizacije povezane s astmom, poboljšao plućnu funkciju i smanjio primjenu ili omogućio prekid liječenja oralnim kortikosteroidima. Uz astmu, čest su komorbiditet i druge alergijske bolesti u dišnom sustavu; alergijski rinitis, sinusitis, kao i nosni polipi. IgE je uključen u patofiziološki mehanizam, koji je u podlozi alergijskog rinitisa i nosnih polipa. Postojeći podaci iz kliničkih ispitivanja govore u prilog učinkovitosti lijeka omalizumab i u tih bolesti, iako nema indikaciju u liječenju istih. Nedavno su završena ispitivanja POLYP1 i POLYP2, u kojima se omalizumab ispitivao u liječenju kroničnog rinosinusitisa s nosnim polipima. Publikacija detalja ovih ispitivanja u stručnom časopisu željno se iščekuje.

SUMMARY – Asthma is a chronic inflammatory disease that is characterized by reversible obstruction of airways, bronchial hyper-reactivity and airway remodeling. The etiology of asthma is multifactorial, with inheritance playing an important role. The aim of our study was to investigate the importance of biomarkers of asthma and the role of plasminogen activator inhibitor-1 (PAI-1) gene as a genetic factor that could be involved in the pathogenesis of asthma. The research was conducted at Jordanovac University Department for Lung Diseases and Croatian Institute of Transfusion Medicine. The research included 149 patients with asthma and 89 healthy individuals. We collected demographic data of both study groups, determined asthma severity using GINA guidelines, and the values of biomarkers and PAI-1 by using laboratory techniques. Based on the results, we concluded that patients with allergic phenotype of asthma were younger, had better lung function and higher levels of IgE. By observing FeNO values, we were not able to distinguish asthmatic patients that had been diagnosed with obstruction of airways from asthmatic patients with normal lung function because FeNO indicates the inflammatory component of disease. The 4G/5G polymorphism of PAI-1 gene did not show any statistically significant difference in the distribution of 4G/4G, 4G/5G and 5G/5G between the group of asthmatic patients and control group.

Plasminogen activator inhibitor-1 (PAI-1) is a glycoprotein which has a role in tissue remodelling after inflammatory processes. The objective is to investigate the frequency of PAI-1 gene polymorphism (4G/5G) in patients with a lung ventilation dysfunction in asthma and allergic rhinitis. Genomic DNA was isolated and genotypes of polymorphism of PAI-1 4G/5G and ABO were determined using the methods of RT-PCR and PCR-SSP. Study group includes 145 adult patients diagnosed with chronic asthma, with all clinically relevant parameters and the laboratory markers of pO2, IgE and eosinophils in sputum and nasal swab. In the processing of data, appropriate statistical tests (Kolmogorov–Smirnov test, median, interquartile ranges, χ 2 and Mann–Whitney U tests) were used. Patients with symptoms of allergic rhinitis were significantly younger and had an almost four time higher levels of IgE (P = 0.001), higher pO2 (P = 0.002) and PEF (P = 0.036), compared to those who do not have these symptoms. Genotype PAI 4G/4G is significantly more common in patients with allergic rhinitis (28.1% vs. 16.1%; P = 0.017) compared to the genotype 5G/5G. Carriers of the genotype 4G/5G also have a borderline statistical significance. There were no statistically significant difference in the incidence of allergic rhinitis in the carriers of any ABO genotypes. The frequency of PAI genotype 4G/4G is significantly more common in patients with allergic rhinitis. The results suggest that the carriers of at least one 4G allele are at a higher risk for developing symptoms of allergic rhinitis in asthma.

Asthma is the most common respiratory disease. It has multiple phenotypes thatcan be partially differentiated by measuring the disease’s specific characteristics—biomarkers. The pathogenetic mechanisms are complex, and it is still a challenge to choose suitable biomarkers to adequately stratify patients, which became especially important with the introduction of biologicals in asthma treatment. Usage of biomarkers and an understanding of the underlying pathobiological mechanisms lead to the definition of endotypes. Asthma can be broadly divided into two endotypes, T2-high and T2-low. The right combination of various biomarkers in different phenotypes is under investigation, hoping to help researchers and clinicians in better disease evaluation since theindividual approach and personalized medicine are imperative. Multiple biomarkers are superior to a single biomarker.

Introduction: The investigation of biomarkers could have a predictive value for the degree of asthma severity, occurrence of exacerbations and response to therapy. Aims: The aim was to investigate the diagnostic value of biomarkers in allergic and non- allergic asthma phenotype. Methods 149 adult asthmatic patients without asthma exacerbation were investigated. We collected information about patient9s age, measured biomarkers: total serum IgE (sIgE), Fractional exhaled nitric oxide (FeNO) and determined their Forced Expiratory volume in 1 second FEV1(L). Distribution of biomarkers between allergic and non-allergic phenotype were analysed by Kolmogorov-Smirnov test. Results: In univariate model, age, sIgE and FEV1 (L) were significantly related to allergic asthma phenotype. These patients are younger (median 56 years) than patients with non-allergic phenotype (median 62.5 years). Among people with allergic phenotype, mean sIgE and mean FEV1 (L) values (300.2kIU/L, 2.3L) are higher than among non-allergic asthma phenotype (60.1kIU/L, 1.8L). The FeNO values do not significantly differ between allergic (24.3 ppb) and non-allergic (15.6 ppb) asthma phenotype. When adjusted for all variables included in model, only sIgE level was significantly associated to the allergic asthma phenotype. Conclusion: We have found that allergic asthmatic patients are younger, have milder degree of asthma severity, better lung function and higher values of total serum IgE and FEV1 than non-allergic. Better lung function could be related to their better respond to treatment with inhaled corticosteroids and cornerstone therapy while patients with non-allergic phenotype are older and could have airways remodelling.

Kronična opstruktivna plućna bolest karakterizirana je trajnom, progresivnom opstrukcijom dišnih putova uzrokovanom upalnom reakcijom u tim putovima i plućnom parenhimu na inhalacijske toksične čestice ili dim. Osnovni su ciljevi farmakološkog liječenja KOPB-a smanjenje simptoma, učestalosti i težine egzacerbacija te poboljšanje podnošenja fizičkog napora i zdravstvenog statusa. Osnova farmakološkog liječenja stabilnoga simptomatskog KOPB-a jesu bronhodilatatori (beta-agonisti i antikolinergici) sami ili u kombinaciji s inhalacijskim kortikosteroidima (ICS). Za pacijente koji imaju trajne simptome preporučuje se redovita primjena dugodjelujućih bronhodilatatora. Oni znatno poboljšavaju plućnu funkciju, kvalitetu života vezanu uza zdravlje i smanjuju učestalost egzacerbacija u usporedbi s placebom. Ukupno gledajući, dugodjelujući muskarinski antagonisti (LAMA) dovode do većeg poboljšanja parametara plućne funkcije, smanjenja učestalosti akutnih egzacerbacija uz manje neželjenih događaja u odnosu prema dugodjelujućim beta2-agonistima (LABA). U pacijenata čija bolest nije dobro kontrolirana primjenom monoterapije preporučuje se kombinacijska terapija koja se sastoji od dva dugodjelujuća bronhodilatatora različita mehanizma djelovanja. Kombinacijska terapija LABA-LAMA znatno poboljšava plućnu funkciju, simptome i zdravstveni status s obzirom na monoterapiju. Sigurnosni profil kombinacije LAMA-LABA usporediv je s LABA-om i LAMA-om kada se daje kao monoterapija. U pacijenata koji su skloni egzacerbacijama kombinacija ICS-a s LABA-om učinkovitija je nego bilo koja od ovih komponenata samostalno u poboljšanju plućne funkcije, zdravstvenog statusa i smanjenja učestalosti egzacerbacija. U bolesnika s teškim i jako teškim stupnjem KOPB-a i povišenim rizikom od egzacerbacija trojna terapija koja se sastoji od ICS-a, LABA-e i LAMA-e dodatno poboljšava plućnu funkciju, reducira učestalost egzacerbacija i smanjuje zaduhu u odnosu prema kombinaciji ICS-LABA., Chronic obstructive pulmonary disease (COPD) is characterized by persistent airflow obstruction caused by chronic inflammatory response of the airways and the lung parenchyma to noxious particles or gases. The main goals of pharmacologic therapy are to reduce symptoms and the frequency and severity of exacerbations as well as to improve exercise tolerance and health status. The mainstays of drug therapy of stable symptomatic COPD are inhaled bronchodilators (beta-agonists and anticholinergics) alone or in combination with inhaled corticosteroids (ICS). Regular use of long-acting bronchodilators is recommended for the management of patients with persistent symptoms. Compared to placebo, long-acting bronchodilators significantly improve lung function and health-related quality of life while reducing exacerbation rates. Overall, long-acting muscarinic antagonists (LAMAs) lead to greater improvement in lung function parameters, reduction in acute exacerbation rates and fewer adverse effects compared with long-acting beta-2 agonists (LABAs). In patients whose disease is not sufficiently controlled with monotherapy, guidelines recommended combination therapy involving two long-acting bronchodilators with differing modes of action. Compared with monotherapy, LAMA/LABA combination therapy significantly improves lung function, symptoms and health status. The safety profile of the LAMA/LABA combination therapy is similar to the safety profiles of LABAs and LAMAs when administered as monotherapy. In patients prone to exacerbations, an ICS combined with LABA is more effective than either component alone in improving lung function, health status and reducing exacerbations. In patients with severe to very severe COPD and increased exacerbation risk, triple therapy consisting of ICS, LABAs and LAMAs additionally improves lung function, reduces exacerbation rates and dyspnea compared to ICS/LABA combination therapy.

Raspodjela krvnih grupa ABO varira diljem svijeta u različitim populacijama, ali i unutar subpopulacija. Cilj rada je prikazati razdiobu 5 glavnih alela ABO sustava (O1, O2, A1, A2 i B) u hrvatskoj populaciji, te ih usporediti s drugim nacijama. Istraživanje je provedeno na 303 uzorka krvi, zdravih, nesrodnih dobrovoljnih davatelja krvi (123 žena, 180 muškaraca) u dobi od 18 do 65 godina. Metode: Nakon izolacije genomske DNA pomoću komercijalnih kolona (QIAamp DNA Blood Mini kit, Qiagen, Njemačka) ili na uređaju MagNA Pure Compact (Roche Diagnostics Corporation, SAD), određeni su genotipovi ABO pomoću metode PCR-SSP. Rezultati: Genotipizacijom je utvrđeno 12 genotipova. Najzastupljeniji genotip je O1O1 (37,2 %), pa slijede O1A1 (27,1 %), O1B (15,8 %), A1B (4,3 %), A1A1 (4,0 %), O1A2 (3,6 %), O1O2 (2,6 %), A1A2 (1,7 %), O2A1 (1,7 %), A2B (1,0 %), BB (0,7 %), O2O2 (0,3 %). Među ispitanicima nisu nađena tri rijetka ABO genotipa: A2A2, O2A2, O2B. Alelne frekvencije iznose: O1 – 0,62; O2 – 0,025; A1- 0,21; A2 – 0,035 i B – 0,11. Razdioba alela ABO u Hrvatskoj je usporediva s drugim europskim narodima. Zaključak: Rezultati genotipizacije ABO krvne grupe kod dobrovoljnih davatelja krvi, koji su reprezentativan uzorak hrvatske populacije, od temeljnog su značenja za istraživanja ABO sustava krvnih grupa kao genetičkog čimbenika rizika za neke bolesti, kao i za antropološka ispitivanja., The frequencies of gene polymorphisms of blood groups serve as markers for populations and races. Distribution of ABO blood groups varies among populations and subpopulations around the world. The aim of the study was to determine distribution of the 5 main alleles of ABO system among Croatian blood donors and compare them with other populations. Material and Methods: The study included 303 samples of healthy unrelated volunteer blood donors, 123 female and 180 male, aged 18-65 years, as a representative sample population of Croatia. After isolation of genomic DNA using commercial columns (QIAamp DNA Blood Mini Kit, Qiagen, Germany) or on the Magna Pure Compact (Roche Diagnostics Corp., USA) device, ABO genotypes were determined by the PCR-SSP method. Results: Twelve of 15 ABO genotypes were identifi ed. The most common was O1O1 (37.30%), followed by O1A1 (27.00%), O1B (15.80%), A1B (4.30%), A1A1 (4.00%), O1A2 (3.60%), O1O2 (2.60%), A1A2 (1.70%), O2A1 (1.70%), A2B (1.00%), BB (0.70%), and O2O2 (0.30%). Three rare ABO genotypes, A2A2, O2A2, and O2B, were not identifi ed. The calculated allele frequencies of the fi ve main alleles were as follows: O1, 0.620; O2, 0,025; A1, 0.21; A2, 0,035; and B, 0.11. In the Croatian population, O1 was found to be the most common allele, followed by A1 and B, while O2 allele was the least prevalent one. Conclusion: The distribution of alleles in Croatia is comparable to other European nations. According to the frequency of B allele, the Croatian population is comparable to Eastern Europe, probably due to migration of the population in the past. Results of ABO blood group genotyping have fundamental importance for research of the ABO system as a genetic risk factor for some diseases, as well as for anthropologic testing.