Serum indicators for the diagnosis of pneumocystis pneumonia

Background: The diagnosis of pneumocystis pneumonia (PCP) is difficult because it requires microscopic examination to identify pneumocystis from induced sputum or BAL fluid. Study objective: To evaluate the usefulness of four serum markers - lactate dehydrogenase (LDH), (1→3) β-D-glucan (β-D-glucan), KL-6, and C-reactive protein (CRP) - in the diagnosis of PCP. Design: Case-control retrospective study. Patients and measurements: We reviewed the medical records of 295 consecutive patients who underwent BAL for the diagnosis of PCP. Differential cell counts in BAL fluid and serum levels of LDH, β-D-glucan, KL-6, and CRP were examined. Oxygenation index was determined using arterial oxygen tension and inspiratory oxygen concentration. Results: Based on the microscopic examination of BAL fluid, 57 patients were PCP positive and 238 patients were PCP negative. There were no significant differences in cell count or differentials in BAL fluid between the positive and negative cases. Serum levels of LDH, β-D-glucan, and KL-6 were significantly higher in PCP-positive patients (p < 0.01). Receiver operating characteristic curves suggest that β-D-glucan was the most reliable indicator. The cut-off level of β-D-glucan was estimated to be 31.1 pg/mL, with which the positive and negative predictive values were 0.610 and 0.980, respectively. In PCP-positive patients, the oxygenation index was decreased and correlated with LDH. Both LDH and β-D-glucan levels were correlated with the proportion of neutrophils in BAL fluid. Conclusions: Serum β-D-glucan is a reliable marker for the diagnosis of PCP. Since BAL procedure is invasive, measuring β-D-glucan should be considered as a primary modality for a diagnosis of PCP, especially for patients with severe respiratory failure.