Pulmonary Function Test Abnormalities in Subacute Cough: A Neglected Tool

Subacute cough is often considered a benign and self-limiting condition, and pulmonary function tests (PFTs) are not routinely performed during this period. This study aimed to evaluate PFT findings in patients with subacute cough compared with those in healthy controls.

This retrospective, cross-sectional study included adults with subacute cough who underwent standardized spirometry, along with age- and sex-frequency matched healthy controls. Forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), and forced expiratory flow at 25-75% of the pulmonary volume (FEF_25-75) were recorded as absolute values and z-scores. Between-group comparisons were performed using analysis of covariance to adjust for age, sex, and height.

A total of 156 patients with subacute cough and 156 controls were analyzed. Patients with subacute cough demonstrated significantly lower FEV₁ and FVC z-scores, and lower FEF_25-75 values and z-scores (all P < 0.001). After adjustment, group differences remained significant for FVC, FEV₁ z-score, and FEF_25-75 (both absolute and z-score). Post-infectious cough was the most common diagnosis (37.8%), followed by asthma (25%); interstitial lung diseases (ILD) were also detected. FVC z-scores, absolute FEF_25-75, and FEF_25-75 z-scores were lower in the obstructive airway disease and ILD subgroups than in the post-infectious cough group. FEF_25-75 z-scores showed the greatest discriminatory ability across diagnostic categories.

Subacute cough encompasses a heterogeneous group of underlying diseases and should not be considered solely post-infectious. Patients with subacute cough may exhibit impaired PFTs, especially FEF_25-75 z-scores. PFTs may provide additional information for the evaluation of subacute cough.