Pulmonary diffusing capacity among individuals recovering from mild to moderate COVID-19: a cross-sectional study

Impaired pulmonary diffusing capacity for carbon monoxide (DLCO) following COVID-19 has been consistently reported among individuals recovering from severe-critical infection. However, most long COVID cases follow non-severe COVID-19. We assessed DLCO among individuals with long COVID recovering from mild to moderate acute illness. A cross-sectional study of adults with long COVID, assessed at a COVID recovery clinic > 3 months following the onset of acute infection, during 2020-2021. Participants subjectively ranked their dyspnea severity based on its impact on their daily living and underwent comprehensive pulmonary function testing (PFT). Clinical correlates for impaired DLCO (defined as < 80%) were assessed using multivariable logistic regression models. A total of 458 individuals, their mean age 45 (SD 16) and 246 (54%) of whom are women, were evaluated at an average of ~ 4 months following acute COVID-19. The most frequent PFT impairment was reduced DLCO, identified among 67 (17%) of the cohort. Clinical correlates of impaired DLCO included women (odds ration [OR] 3.64, 95% confidence interval [CI] 1.78-7.45, p < 0.001), cigarette smoking (OR 2.25, 95% CI 1.14-4.43, p = 0.019), and moderate-severe dyspnea (OR 2.77, 95% CI 1.39-5.50, p = 0.004). BMI inversely correlated with DLCO (OR 0.90, 95% CI 0.85-0.96 per 1 unit, p = 0.002). Impaired DLCO was not uncommon among individuals recovering from mild to moderate COVID-19. Women are at a greater risk, and subjective dyspnea correlated with impaired DLCO. Clinicians can rely on self-reported significant dyspnea to guide further assessment.