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HIV False-Positive Test in the Setting of CD4 Lymphocytopenia
Hussien Mohamed1, Hanna D Hedriana2, Emily A Holbrook3
1Emergency Medicine, Christiana Care, Newark, USA.
Insights
A unique case of a false-positive HIV test with a low CD4 count was identified in the Emergency Department. This highlights the importance of further testing to confirm HIV status, especially in equivocal results.
Area of Science:
- Infectious Diseases
- Immunology
- Clinical Diagnostics
Background:
- Revised CDC guidelines prompted the implementation of non-targeted Emergency Department (ED)-based HIV screening.
- The Abbott Alinity 4th generation HIV-1/2 antigen (Ag)/antibody (Ab) immunoassay is used for initial screening.
- The diagnostic algorithm involves confirmatory antibody testing after initial reactive results.
Observation:
- Acute HIV infection (acutes) can present with p24 Ag but negative confirmatory Ab tests, mimicking false positives.
- "Equivocal" results require viral load testing for definitive HIV status determination.
- A rare subset of false-positive cases exhibit idiopathic CD4 lymphocytopenia (reduced CD4+ count).
Findings:
- A patient presented with two separate instances of reactive fourth-generation HIV Ab/p24 Ag tests.
- Despite presenting with lymphopenia and a reduced CD4 count, the patient's symptoms resolved.
- HIV RNA PCR testing was negative, confirming a false-positive result without HIV infection.
Implications:
- This case highlights a unique false-positive scenario with reactive p24 Ag and concurrent low CD4 count, unrelated to HIV infection.
- The findings underscore the complexity of interpreting "equivocal" HIV test results, particularly when accompanied by lymphopenia.
- Accurate diagnosis is crucial, as a low CD4 count is typically indicative of significant HIV infection, making this case an important diagnostic consideration.
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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