Performance Characteristics of Real-Time Quantitative PCR and Cycle Threshold (Ct) Values for the Diagnosis of Pneumocystis jirovecii pneumonia in Hospitalized Patients

Purpose: Pneumocystis jirovecii pneumonia (PCP) is a critical opportunistic infection that predominantly affects immunocompromised patients, particularly those with underlying diseases, and leads to significant morbidity and mortality. This study aimed to enhance the diagnostic accuracy and treatment strategies for PCP by investigating the clinical and laboratory characteristics of patients with suspected PCP and focusing on the diagnostic performance of qPCR and Cycle Threshold (Ct) values. Patients and Methods: We retrospectively analyzed the clinical and laboratory data of 249 patients at the Central Hospital of Shaoxing University between 2024 and 2025. Clinical characteristics, qPCR test performance, and Ct values were compared between these PCP diagnostic groups, revealing that 8 were classified as definite cases, 32 as probable, and 88 as non-PCP. Results: The definite group exhibited significantly lower lymphocyte percentages and counts than the probable and non-PCP groups (P =0.003 and P =0.009, respectively). Additionally, beta-d-glucan (BDG) levels were elevated in the definite group (p< 0.001), indicating their potential as reliable biomarkers for PCP diagnosis. The qPCR assay demonstrated high sensitivity (95%) and specificity (99%) in detecting PCP between the PCP and non-PCP groups, with an optimal cut-off Ct value of 35.305 (area under the curve (AUC)=0.98). Correlations among Ct values, lymphocyte percentages, and lactate dehydrogenase (LDH) levels were observed, underscoring the prognostic implications of these laboratory parameters. Conclusion: Our findings support the integration of qPCR Ct values and BDG in clinical settings to refine the diagnostic criteria and enhance patient management strategies for PCP, paving the way for further research on additional biomarkers and their roles in prognostic assessments. Keywords: qPCR, cycle threshold Ct values, Pneumocystis jirovecii pneumonia, clinical indicators