1061 - False Positive Human Immunodeficiency Virus Testing Due to Acute Hepatitis A Infection: A Case Series

Background: In our urban, underserved patient population, Human Immunodeficiency Virus (HIV) is hyper-endemic, and HIV screening is frequently performed.  Although HIV screening tests have high specificity, false positives can occur.  Numerous reasons for false positive testing have been cited, including vaccinations, autoimmune diseases, and viral infections.  In 2019, Philadelphia experienced a large Hepatitis A outbreak, during which time false positive HIV screening tests were discovered.  Our aim was to further describe these patients who had been diagnosed with acute Hepatitis A infection and in whom false positive HIV testing had occurred.

Methods: We conducted a retrospective chart review of adult patients admitted to our hospital between January 2017 and December 2019 who had a positive Hepatitis A Virus (HAV) IgM.  Demographics, HIV tests, viral hepatitis tests, and liver tests were recorded. False positive HIV was defined as a positive HIV screen (p24 antigen and HIV-1 and 2 antibody combo), followed by a negative differentiation assay for HIV-1 and 2 antibodies, combined with a negative HIV PCR.

Results: A total of 156 unique patients were found to have acute HAV, with 138 cases identified in 2019.  Of these, 3 patients had confirmed false positive HIV testing, and 1 patient had suspected false positive HIV testing (HIV-2 differentiation assay indeterminate, with very low local prevalence of HIV-2), for a false positive test rate of 2.6% (4/156).  Ages ranged from 36-47 years, 3 were male, and 2 were persons who injected drugs (PWID).  Three patients had prior negative HIV testing.  Two patients had fevers during admission, but none of the four were febrile at the time of HIV test collection. Three patients had elevated transaminases, and two had abnormal coagulation testing.  Coinfection with Hepatitis C was found in three patients.  One patient had follow-up HIV testing performed, which was negative.

Conclusion: To our knowledge, this is the first report of false positive HIV testing related to acute HAV.  Prevalence of false positives was low, but awareness can facilitate patient counseling. With low sample size, conclusions cannot be drawn about risk factors related to false positive testing.