Diagnostic accuracy of blood eosinophils in comparison to other common biomarkers for identifying sputum eosinophilia in patients with chronic cough.

Background: Sputum eosinophilia is a treatable trait for chronic cough. It is currently not clear whether the blood eosinophil counts could be used to identify sputum eosinophilia in patients with chronic cough. This study aimed to evaluate the diagnostic accuracy of blood eosinophils in comparison to other common type 2 biomarkers for identifying sputum eosinophilia in patients with chronic cough. Methods: In this prospective study, a total of 658 patients with chronic cough were enrolled. Induced-sputum test, routine blood test, total immunoglobulin E (TIgE), and fractional exhaled nitric oxide (FeNO) level were measured. The percentage of sputum eosinophils (Eos%) ≥ 2.5% was defined as sputum eosinophilia. The area under the curve (AUC) of blood eosinophil counts, TIgE, and FeNO alone or in combination for predicting sputum eosinophilia were analyzed. Results: The AUC of blood eosinophil counts for predicting sputum eosinophilia in chronic cough patients was moderate [0.826 (0.767-0.885)], as compared to that of FeNO [0.784 (0.720-0.849), P = 0.280] and TIgE [0.686 (0.613-0.760), P = 0.001]. When combining blood eosinophil counts and FeNO for detecting sputum eosinophilia, a significantly larger AUC [0.868 (0.814-0.923), with a sensitivity of 84.2% and a specificity of 82.8%] was yielded, as compared to each single marker alone (all P < 0.05). Conclusions: Blood eosinophil counts have a moderate diagnostic value for identifying sputum eosinophilia in patients with chronic cough, while a combination of blood eosinophil counts and FeNO measurement can provide additional predictive value.