HIV False-Positive Test in the Setting of CD4 Lymphocytopenia

TL;DR

A patient had a false positive HIV test with low CD4 count, highlighting the need for confirmatory testing in such cases.

Contribution

The paper presents a rare case of a false positive HIV test with a low CD4 count unrelated to HIV infection.

Findings

The patient had a reactive fourth-generation HIV test but no detectable HIV RNA.

The patient exhibited idiopathic CD4 lymphocytopenia without HIV infection.

False positives with low CD4 counts are uncommon and require further investigation.

Abstract

In 2016, we implemented a non-targeted Emergency Department (ED)-based HIV screening program at our academic medical center following revised CDC guidelines utilizing the Abbott Alinity 4th generation HIV-1/2 antigen (Ag)/antibody (Ab) immunoassay (Abbott Laboratories, Abbott Park, IL). Following the CDC algorithm, after reactive fourth-generation testing, HIV-1/2 Ab testing is conducted. Patients undergoing acute seroconversion (acutes) may express p24 Ag but have a negative confirmatory Ab test. Acutes have the same laboratory signature during the ED encounter as those that are false positive (False +), and the two patient groups are denoted as “equivocals” until viral load testing specifies a definitive HIV status. Among False + patients (Ab/Ag positive, Ab negative, viral load undetectable), there have been limited studies on those also demonstrating a reduction in CD4+ count, an uncommon phenomenon known as “idiopathic CD4 lymphocytopenia.” We review a patient with a reactive fourth-generation HIV Ab/p24 Ag test on two separate occasions. Despite lymphopenia with a reduced CD4 count, his symptoms resolved, and an RNA PCR test did not detect any presence of HIV (False +). This patient was unique as False + patient with p24 Ag reactive, as well as a coincidental low CD4 count in the absence of HIV infection. A low CD4 count is often a sign of significant HIV infection.

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