Diagnostic Value of Serological Markers and Quantitative Real-Time PCR in Patients With Invasive Candidiasis

Objective To evaluate the clinical diagnostic value of serological markers, including the 1, 3-β-D-glucan test (G-test), Candida mannan (Mn) antigen, Candida mannan IgG antibody (Mn-IgG), and quantitative real-time PCR(qPCR) in patients with invasive candidiasis (IC). Methods This study included 79 patients with culture-proven IC (IC group) and 83 patients without IC (non-IC group) at West China Hospital, Sichuan University between December 2022 and December 2024. Serum samples were tested for the G test (chemiluminescence), Mn antigen (ELISA), Mn-IgG (chemiluminescence), and qPCR. The diagnostic sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of individual and combined tests were calculated. Diagnostic performance was assessed using receiver operating characteristic (ROC) curve analysis. ResultsThe sensitivity, specificity, PPV, and NPV of the three serological markers for IC diagnosis when used individually were as follows: G test, 62.03%, 94.87%, 92.45%, and 71.15%; Mn antigen, 65.63%, 86.59%, 79.25%, and 76.34%; Mn-IgG antibody, 31.65%, 87.95%, 71.43%, and 57.48%. Combined detection of the G test, Mn antigen, and Mn-IgG increased sensitivity to 73.44%. Based on ROC curve analysis, the AUCs for diagnosing IC using each serological marker were: G test, 0.862 (95% CI: 0.803-0.922); Mn test, 0.853 (95% CI: 0.790-0.915); Mn-IgG, 0.603 (95% CI: 0.514-0.692). The combined AUCs for G test + Mn test, G test + Mn-IgG, and G test + Mn test + Mn-IgG were 0.875 (95% CI: 0.809-0.925), 0.869 (95% CI: 0.805-0.917), and 0.875 (95% CI: 0.809-0.924), respectively, demonstrating superiority over individual tests. The sensitivity, specificity, PPV, and NPV of qPCR for IC diagnosis were 100.00%, 98.80%, 98.75%, and 100.00%, respectively. Using culture strain identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) as the gold standard, qPCR demonstrated diagnostic concordance rates of 100.00% for Candida albicans, 100.00% for Candida tropicalis, 94.40% for Candida glabrata, and 90.00% for Candida parapsilosis. ConclusionThe combined use of the G test, Mn antigen, and Mn-IgG antibody increases diagnostic sensitivity and facilitates early diagnosis of IC. qPCR demonstrates excellent diagnostic performance for IC, enabling species-level identification of common Candida species associated with IC and detection of other Candida species. It also shows consistency with clinical culture methods.