Abstract
BACKGROUND: Blood eosinophil counts (BECs) show moderate fluctuations over time but their long-term variability and clinical relevance in the general population remain unclear. We hypothesise a temporal variation of BECs over two visits (V1 and V2; 4.3±0.6 years) in the population-based Austrian LEAD study. METHODS: Adults (n=6932) were categorised by their BEC levels: consistently high (BEC(HIGH), ≥210 cells·µL(-1) at V1 and V2), consistently low-normal (BEC(LOW/NORMAL), <210 cells·µL(-1) at V1 and V2), variably increasing (BEC(INCREASE), <210 cells·µL(-1) at V1 and ≥210 cells·µL(-1) at V2) and variably decreasing (BEC(DECREASE), ≥210 cells·µL(-1) at V1 and <210 cells·µL(-1) at V2). Associations with lung function and respiratory conditions were analysed. RESULTS: Most individuals remain within their baseline BEC threshold (83.7% in BEC(LOW/NORMAL) and 67.3% in BEC(HIGH)). BEC variability exceeded the normal range (-30 to 60 cells·µL(-1)) BEC(INCREASE) (+150 cells·µL(-1)) and BEC(DECREASE) (-144 cells·µL(-1)) groups. BEC variability significantly affected lung function (ΔFEV(1)-BEC(DECREASE), 26.14 (95.75-46.52) and BEC(INCREASE), -21.58 (-38.41- -4.75); and ΔFVC-BEC(DECREASE), 28.74 (8.14-49.34) and BEC(INCREASE), -20.78 (-37.73- -3.83)). BEC(HIGH) individuals were most associated with respiratory symptoms. CONCLUSIONS: BEC is not a static biomarker; longitudinal variability predicts changes in lung function. Current guidelines rely on single time-point BEC measurements, but our findings suggest that repeated assessments and the use of thresholds to determine normal BEC variability over time may better guide treatment decisions in high-risk patients.