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False positive rate of rapid oral fluid HIV tests increases as kits near expiration date
Shelley N Facente1, Teri Dowling, Eric Vittinghoff
1HIV Prevention Section, San Francisco Department of Public Health, San Francisco, California, United States of America. shelley@facenteconsulting.com
Background:
Because a recent cluster of false positive results on the OraQuick ADVANCE Rapid HIV-1/2 Antibody Test occurred in San Francisco on test kits close to their expiration date, we decided to assess the relationship between time to expiration and rate of false positive results from tests used with oral fluid.
Methodology/Principal Findings:
We analyzed results of 20,904 tests with either an initial HIV-negative result (n = 20,828) or a preliminary positive result that was then negative on confirmatory tests (n = 76). We computed specificity for kits with time to expiration from < or = 1 to > or = 6 months, with exact binomial confidence intervals, then used logistic regression to estimate the independent association of time to expiration with false positive results, adjusting for site and technician effects. For 1,108 kits used in the last month before expiration, specificity was 98.83% (95% exact binomial confidence interval (CI) 98.00%-99.37%); the upper bound is below the claimed specificity of 99.60%. After adjustment using regression standardization for the effects of site, test lot, and technician factors, adjusted specificity in the last month before expiration was 99.18% (95% bootstrap confidence interval 98.60-99.57%).
Conclusions/Significance:
We found that specificity of the OraQuick ADVANCE with oral fluid declined significantly with < or = 1 month remaining to expiration, leaving little margin for error from other sources.
