An unexpected association between the blood bilirubin level and eosinophil count

Purpose: Little is known about blood markers related to eosinophils in healthy individuals. We aimed to identify blood markers from routine tests associated with blood eosinophil count (BEC) in healthy individuals. Methods: Based on the complex interactions among blood markers, we used comprehensive analysis methods (regression, Bayesian network [BN], and partial correlation) and a health check-up database. To test consistency, we repeated the analysis using data from 3 check-ups of the same healthy individual. Results: A total of 12,625 individuals were enrolled in this study. Four groups were defined according to sex and smoking status: nonsmoking men (n=1,737), smoking men (n = 6,518), nonsmoking women (n = 3,995), and smoking women (n = 375). The blood bilirubin and & gamma;-glutamyltransferase levels showed significant associations with BEC by regression analysis. However, BN analysis found that only the bilirubin node was directly connected to the BEC node. By partial correlation analysis, the blood bilirubin level showed significantly negative association with BEC. The same results were obtained across all the 3 health check-ups, except in smoking women. In addition, a lower blood bilirubin level predicted a significantly elevated BEC (especially & GE; 200/& mu;L). The blood bilirubin levels measured at 3 time-points were significantly associated with BEC in men and nonsmoking women. Conclusion: The blood bilirubin level, which is easily obtained by routine test in clinical practice, may be a useful marker for BEC.