How consistent are blood eosinophil counts in a general population?

Rationale: It is well known, that normal values of blood eosinophil counts (EOS_b) have a broad range, which is age/sex dependent in general populations (GP). The longitudinal consistency of EOSb in a GP is scarcely investigated. Methods: We investigated the consistency of EOS_b in the Austrian LEAD study, a single-centred, observational, population-based cohort from 6-80 years. We analysed EOS_b in 7774 participants (total cohort; tGP) and in 2720 participants with non EOS-associated disease (no allergy, asthma, COPD,metabolic syndrome/obesity, current smoking, HES reported - healthy subgroup; HSP) at baseline and at follow up after 4 years. EOS_b were categorized in low (0-99 cells/µl), medium (100-299 cells/µl) and high (>300 cells/µl). The individual upper/lower limit of normal (ULN/LLN) was calculated for baseline and follow up EOS_b by using the LMS-method and the calculation of z-scores. Proportion of probands were expressed as ULN. Results: In the tGP 27.25% had low EOS_b, 59.26 % medium EOS_b, and 13.49% high EOS_b; in HSP, 34.6 % had low EOS_b, 55.5% medium EOS_b, and 9.83% high EOS_b. Changes from ULN happened only in 6.18% of tGP/ 4.35% of HSP and from>ULN to Conclusion: In the GP and in a HSP the overall proportion of high EOS_b is small. Also, the longitudinal consistency of EOS_b values is high, which may strengthen the value of a single measurement of EOS_b as a biomarker.