Comparison of urine and serum Western Blot tests for HIV-1 infection in a high risk population

We compared results of urine¹ and serum HW-1 Western Blot (WB, Cambridge Biotech, Inc) tests in a high risk population. Matched sera and urines from 382 persons (292 M, 90 F) attending a substance abuse program in NYC were collected from specimens remaining after routine testing was completed, and encoded to ensure privacy. Sera were frozen and urines refrigerated until testing. Urines were tested using a modification of the method recommended for serum testing; sera were tested according to the manufacturer's recommendation. When WB results are compared, 71 results were positive and 200 were negative by both methods. There were 7 "discrepant" pairs for which one test method was positive, as follows: 2 urine WB negative/serum WB positive; 1 urine WB indeterminate/serum WB positive; 1 urine WB positive/serum WB negative; and 3 urine WB positive/serum WB indeterminate results. A high proportion of serum WB results (n=107, 28%) were indeterminate, due to presence of nonviral bands, single bands, or multiple low density bands, hi contrast, only 2 (0.5%) urine WB results were indeterminate, and nonviral bands were not noted. Overall, detection of positives was similar (urine = 75, serum = 74) by both HIV-1 WB methods.