Analysis of Paired Serum, Urine and Filter Paper Blood Specimens for Presence of Filarial Antigen by Immunoradiometric Assay

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Abstract
Paired serum, urine, and finger-prick whole blood dried on filter paper were analyzed by immunoradiometric assay (IRMA) for filarial antigen using Brugia malayi-specific rabbit antibody. Nine sera and 6 urines from the 10 paired serum-urine samples obtained from individuals with microfilaremia contained IRMA detectable filarial antigen. In contrast, all serum and urine specimens from patients with chronic infections, endemic and non-endemic controls were negative. Whole blood eluted from filter paper spots contained IRMA detectable material; their degree of positivity agreed well with IRMA binding levels obtained with paired urines. Reduced recovery of antigen dried on filter paper was observed at antigen levels < 10 ng/ml equivalents, presumably due to irreversible absorption onto the filter paper. Urine and finger-prick filter paper blood specimens can be used in the diagnosis of microfilaremic infections that have been associated with circulating antigen in the blood.