Serum (1,3)-Beta-d-Glucan has suboptimal performance for the diagnosis of Pneumocystis jirovecii pneumonia in cancer patients and correlates poorly with respiratory burden as measured by quantitative PCR

Objective: Non-HIV immunocompromised patients with Pneumocystis jirovecii pneumonia (PCP) have lower fungal load than those with AIDS, potentially affecting the accuracy of diagnostic biomarkers. Therefore, we investigated the performance of serum (1,3)-Beta-d-Glucan (BDG) in conjunction with quantitative Pneumocystis jirovecii PCR (qPCR) in non-HIV cancer patients.

Methods: We reviewed records of non-HIV cancer patients and classified them as definite, probable, or possible PCP cases, according to clinicoradiological features, microscopy findings, and qPCR results in bronchoscopy specimens. We evaluated the diagnostic performance of serum BDG and its correlation with qPCR results.

Results: We identified 101 PCP patients (73 definite/probable, 28 possible) and 74 controls. Correlation of BDG and qPCR was low among all 101 qPCR-positive patients (Spearman's = 0.38) and in definite/probable PCP cases (Spearman's = 0.18). Considering all qPCR-positive patients, BDG showed consistently low sensitivity at different cutoffs. Among definite/probable cases, the diagnostic accuracy of BDG remained poor, yet slightly improved with high qPCR thresholds (AUC = 0.86 at ≥2000 DNA copies/mL). BDG had a low PPV but excellent NPV across different qPCR and BDG cutoffs.

Conclusions: BDG and qPCR levels correlate poorly in non-HIV cancer patients with PCP. BDG diagnostic performance is suboptimal but a negative test may be useful to rule out PCP in this population.