Detection of circulating filarial antigen in paired serum and hydrocele fluid from men with hydrocele in Ranchi, India.

BACKGROUND: Circulating filarial antigen (CFA) assays complement microscopy for detecting active Wuchereria bancrofti infection. This study compared CFA detection in paired serum and hydrocele-fluid specimens from men with hydrocele in Ranchi, India. METHODS: In this cross-sectional study, 77 men undergoing hydrocele surgery provided nocturnal blood, serum, and hydrocele-fluid specimens. Blood and hydrocele fluid were examined microscopically for microfilariae. Paired serum and hydrocele-fluid specimens were tested using a commercial human filarial-antigen ELISA. Paired CFA results were compared using the exact McNemar test, and agreement and diagnostic-performance measures were calculated with 95% confidence intervals (CIs). RESULTS: Microfilariae were detected in nocturnal blood from 4/77 participants (5.19%) and in no hydrocele-fluid specimen. Serum CFA-ELISA was positive in 9/77 (11.69%), whereas hydrocele-fluid CFA-ELISA was positive in 4/77 (5.19%). Four participants were positive in both matrices, five were serum-positive/hydrocele-fluid-negative, and 68 were negative in both. The paired positivity difference was 6.49 percentage points (95% CI, 0.48-14.32), and the exact McNemar p value was 0.0625. Overall agreement was 93.51% (Cohen kappa, 0.586; 95% CI, 0.266-0.905). Relative to serum CFA-ELISA, hydrocele-fluid testing had 44.44% sensitivity and 100% specificity. CONCLUSIONS: CFA was detected less frequently in hydrocele fluid than in serum. Hydrocele fluid cannot replace serum for CFA-based diagnosis in this setting.