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.