Serum markers in interstitial pneumonia with and without Pneumocystis jirovecii colonization: a prospective study

BACKGROUND In patients with chronic respiratory disease, Pneumocystis jirovecii (P. jirovecii) colonization is observed, and may influence disease progression and systemic inflammation. Pneumocystis pneumonia causes interstitial changes, so making a diagnosis of PCP in patients who have interstitial pneumonia (IP) with P. jirovecii colonization is sometimes difficult based on radiography. METHODS This study investigated the prevalence of P. jirovecii colonization in IP patients and assessed pulmonary injury due to P. jirovecii colonization by measurement of serum markers (KL-6, SP-A, SP-D, and (1-->3) beta-D-glucan (beta-D-glucan)) and the peripheral lymphocyte counts, prospectively. A total of 75 patients with idiopathic pulmonary fibrosis (n = 29), collagen vascular-related interstitial pneumonia (n = 19), chronic bronchitis or pneumonia (n = 20), and Pneumocystis pneumonia (n = 7) were enrolled in this prospective study. P. jirovecii DNA was detected in sputum samples, while serum markers and the lymphocyte count were measured in the peripheral blood. RESULTS IP patients (idiopathic pulmonary fibrosis and collagen vascular-related IP) who received oral corticosteroids had a high prevalence of P. jirovecii colonization (23.3%). In IP patients, oral corticosteroid therapy was a significant risk factor for P. jirovecii colonization (P < 0.05). Serum markers did not show differences between IP patients with and without P. jirovecii colonization. The beta-D-glucan level and lymphocyte count differed between patients with Pneumocystis pneumonia or P. jirovecii colonization. CONCLUSION Serum levels of KL-6, SP-A, SP-D, and beta-D-glucan were not useful for detecting P. jirovecii colonization in IP patients. However, the serum beta-D-glucan level and lymphocyte count were useful for distinguishing P. jirovecii colonization from pneumocystis pneumonia in IP patients.