Evaluation and Clinical Impact of the Combination of Wako® (1,3)-β-D-Glucan in Serum and RT-PCR in Oral Wash for Pneumocystis jirovecii Infection Diagnosis: A Retrospective Cohort Study

Pneumocystis jirovecii pneumonia (PCP) is an opportunistic infection in immunocompromised patients, with a complex diagnosis due to its colonizing role. Current guidelines recommend microbiological confirmation through direct microscopy of lower respiratory tract samples, 1,3-β-D-glucan (BDG) serum testing, or RT–PCR detection in lower respiratory samples. However, non-invasive diagnostic alternatives, such as oral wash RT–PCR combined with BDG serum levels, could be an option for non-intubated and non-candidates to bronchoscopy patients in a real clinical setting. A retrospective study analysed 49 patients with suspected PCP at Hospital Universitario La Paz (Madrid, Spain) between January 2020–March 2025. Patients underwent to serum BDG (Wako®, ≥7 pg/mL) and P. jirovecii RT–PCR in oral wash tests. The study assessed the impact of time of symptoms and treatment on microbiological findings, and the clinical utility of combining test for PCP diagnosis. Among the 49 patients, 12 (24.5%) had a positive P. jirovecii RT–PCR in oral wash, and 12 of them (85.7%) also a positive BDG. Median BDG was 27.1 (IQR: 14.4–100.7) pg/mL for positive patients (p < 0.05). Patients with (+)BDG/RT–PCR showed a longer symptom duration compared to negative (p > 0.05). Previous PCP prophylaxis/treatment showed a reduce on P. jirovecii RT–PCR results (p > 0.05). Combining tests could be useful in patients who are not candidates for bronchoscopy (p < 0.05) and influenced treatment decisions, reducing unneeded PCP treatments in (-)RT–PCR/BDG in immunosuppressed patients with high pretest value. P. jirovecii RT–PCR in oral wash showed to be good screening assay in patients without PCP treatment/prophylaxis and BDG as appears to serve as a complementary diagnostic tool for confirming PCP infection, primarily in prolonged infectious conditions. This strategy could help optimize treatment decisions reducing the need for invasive procedures. Further multicentric studies are needed to validate the combination test results and assess cost-effectiveness in clinical practice.