Filaria Antigen Test

The test is a qualitative, point-of-care diagnostic tool that detects Wuchereria bancrofti in human blood serum or plasma. There are mainly three laboratory methods used for diagnosing active infections namely demonstration of microfilariae (mf) in the night blood specimens, detection of circulating filarial antigens (CFA) released in the body by adult worms and detection of filarial DNA in human blood by polymerase chain reaction.

There is no special preparation required for the test however it’s recommended to advise the healthcare advisor or the doctor about any ongoing medications or any current medical treatment to avoid any discrepancy in the test reports. Remember to listen to the doctor's instructions which may differ as per the patient's’ conditions.

The geometric mean titre of the sera samples collected during night is 11 units/ml for non-endemic normal and 601.2 units/ml for mf carriers. The specificity of the assay on sera samples which have been collected during the night is always 100% and the sensitivity 96.8% while the positive and negative values are 100% and 95.2% respectively.

The antigen positivity of the filter paper samples which are collected during morning hours is 93.3% which is usually 76.6% and 86.7% during afternoon and in the evening hours respectively. To be noted, a significant association is observed between antigenemia levels and mf density in the blood samples collected during the night. The reports shall be thoroughly explained to the patient by the concerned person, mostly the respective doctor taking care of the case and if no proper information is retrieved or if there are not much specific details concerning the cause then there may be some other tests required.

Finger prick blood is collected into heparinized capillary tubes and stored in a cooler and tubes are centrifuged while plasma are separated and stored at -20C. Samples are tested in duplicate and kit control standards (S1-S7) and a conjugate control are also tested in duplicate on each plate. Usually, blood samples are collected from 63 microfilariae (mf) carrier during different time periods in a day on filter paper discs as well as venous blood for sera. The filarial antigens in the samples are determined using the Og4C3 filarial antigen assay and the sensitivity of the assay on sera and filter paper samples collected during night and those collected during different time intervals of the day are compared with those of the membrane filtration technique which is used as a gold standard.