Utility of procalcitonin for differentiating cryptogenic organising pneumonia from community-acquired pneumonia.

Background This study aimed to investigate the usefulness of inflammatory biomarkers such as white blood cell (WBC) count, C-reactive protein (CRP) and procalcitonin (PCT) for differentiating cryptogenic organising pneumonia (COP) from community-acquired pneumonia (CAP). Methods COP patients hospitalised in Kurashiki Central Hospital between January 2010 and December 2017 whose WBC counts and CRP and PCT levels were measured were investigated retrospectively, and their results were compared with those of hospitalised CAP patients who were prospectively enrolled between October 2010 and November 2017. Definite COP was defined by specific histopathological findings, and possible COP was defined as a consolidation shadow on chest computed tomography and lymphocyte dominance in bronchoalveolar lavage fluid in the absence of specific histopathological findings or lung specimens. The discriminatory abilities of WBC counts, CRP and PCT were evaluated by receiver operating characteristic (ROC) curve analysis. Results There were 56 patients in the entire COP group, 35 (61.4%) with definite COP, and 914 CAP patients. All three biomarkers were significantly lower in COP than in CAP. The AUC value of PCT in all COP patients was 0.79, significantly higher than of both CRP (AUC 0.59, p < 0.001) and WBC (AUC 0.69, p = 0.048). In definite COP patients, the AUC value of PCT was 0.79, which was also significantly higher than of both WBC (AUC 0.64, p = 0.006) and CRP (AUC 0.64, p = 0.001). Conclusions PCT is a more useful biomarker for differentiating COP from CAP than WBC count or CRP. However, PCT should be used as an adjunct to clinical presentation and radiological findings.