Longitudinal variability of blood eosinophils impact lung function decline in the general population

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.

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.

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 (ΔFEV₁-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.

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.