Young sportsmen demonstrate pronounced daily variations of hematological values – are traditional reference ranges compromised?

Diurnal variations of patients’ laboratory parameters, including clinical blood test (CBT) cause considerable interpretation problems; it is unclear if these variations are physiological or disease-related. Narrowing of daily testing schedule is the accepted solution, still, it’s not always possible in hospital setting and its effectiveness has not been studied. 8-17 years old sport school trainees have had CBT regularly performed in Children’s Clinical University Hospital as a part of obLīgatory yearly checkup; the cohort may be tentatively considered as a healthy model. We analyzed 15068 anonymized CBT tests (Sysmex XN2000) taken between 8.00 and 15.00. IBM SPSS v25 was used for statistical analysis. The study revealed pronounced variations within the 8.00–15.00 interval: WBC varied by 14%, absolute NEU by 27%, LYM by 12%, EO by 20%, MON by 14%, PLT and RBC by 4%. WBC, NEU, LYM and MON increased during the time, EO and RBC decreased and PLT peaked at noon. All differences were highly significant in Kruskal-Wallis test. The dynamics were similar in age groups (8-12 and 13-17 years) and in genders. The study demonstrated significant and consistent fluctuations of CBT parameters in healthy children and adolescents at 8-hour interval; 24-hour variations may be even greater. Leukocytes were more variable than platelets and red cells. The findings prove that diurnal changes in patients are not only disease-related, but are at least partly due to normal biological rhythms. These variations in our study were by their size comparable or larger than differences between age groups and genders that are traditionally incorporated in reference ranges, and thus must not be ignored. Sharp and asynchronous dynamics of blood parameters suggest that strict fixing of testing time is not really practical and may be misleading, a more elastic approach to testing schedule and to definition of normal values is necessary.