Comparison of Multispot EIA with Western blot for confirmatory serodiagnosis of HIV

Abstract

Background: Recent improvements in the sensitivity of immunoassays (IA) used for HIV screening, coupled with increasing recognition of the importance of rapid point-of-care testing, have led to proposals to adjust the algorithm for serodiagnosis of HIV so that screening and confirmation can be performed using a dual or triple IA sequence that does not require Western blotting for confirmation. One IA that has been proposed as a second or confirmatory test is the Bio-Rad Multispot(®) Rapid HIV-1/HIV-2 Test. This test would have the added advantage of differentiating between HIV-1 and HIV-2 antibodies.

Objective: To compare the sensitivity and type-specificity of an algorithm combining a 3rd generation enzyme immunoassay (EIA) followed by a confirmatory Multispot with the conventional algorithm that combines a 3rd generation EIA (Bio-Rad GS HIV-1/HIV-2 Plus O EIA) followed by confirmatory Western blot (Bio-Rad GS HIV-1 WB).

Methods: 8760 serum specimens submitted for HIV testing to the New York City Public Health Laboratory between May 22, 2007, and April 30, 2010, tested repeatedly positive on 3rd generation HIV-1-2+O EIA screening and received parallel confirmatory testing by WB and Multispot (MS).

Results: 8678/8760 (99.1%) specimens tested WB-positive; 82 (0.9%) tested WB-negative or indeterminate (IND). 8690/8760 specimens (99.2%) tested MS-positive, of which 14 (17.1%) had been classified as negative or IND by WB. Among the HIV-1 WB-positive specimens, MS classified 26 (0.29%) as HIV-2. Among the HIV-1 WB negative and IND, MS detected 12 HIV-2.

Conclusion: MS detected an additional 14 HIV-1 infections among WB negative or IND specimens, differentiated 26 HIV-1 WB positives as HIV-2, and detected 12 additional HIV-2 infections among WB negative/IND. A dual 3rd generation EIA algorithm incorporating MS had equivalent HIV-1 sensitivity to the 3rd generation EIA-WB algorithm and had the added advantage of detecting 12 HIV-2 specimens that were not HIV-1 WB cross-reactors. In this series an algorithm using EIA followed by MS would have resulted in the expedited referral of 38 specimens for HIV-2 testing and 40 specimens for nucleic acid confirmation. Further testing using a combined gold standard of nucleic acid detection and WB is needed to calculate specificity and validate the substitution of MS for WB in the diagnostic algorithm used by a large public health laboratory.