Understanding Lab Tests for False Positive Results
Written by Private MD Labs Medical Writing Team • Last Updated: September 8, 2025
A false positive result occurs when a lab test incorrectly indicates the presence of a condition, infection, or antibody when it is not actually present. While false positives are relatively uncommon, they can occur with various blood tests and may require confirmatory testing to verify the initial results.
Top Recommended Test
Hepatitis B Surface Antibody, Qualititative
This test measures antibodies against Hepatitis B surface antigen, typically indicating immunity from vaccination or past infection. Rarely, a positive result may be a false positive, suggesting immunity when the person has not actually been infected with or vaccinated against Hepatitis B. Confirmatory testing may be needed to verify true immunity status.
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Why False Positive Results Occur
False positive results can happen due to several factors including cross-reactivity with other substances, autoimmune conditions, recent vaccinations, or technical laboratory issues. Understanding which tests are more prone to false positives helps healthcare providers interpret results appropriately and determine when additional testing is needed.
Other Relevant Tests
Cytomegalovirus (CMV) Antibodies, IgM, Quantitative
This test detects IgM antibodies against CMV, which typically indicate a recent or active infection. Occasionally, other viral infections or autoimmune disorders can trigger the production of CMV IgM antibodies, leading to false positive results. This is more commonly observed in people with autoimmune diseases, requiring additional testing for confirmation.
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Importance of Confirmatory Testing
When a false positive is suspected, healthcare providers may recommend repeat testing, alternative test methods, or additional blood work to confirm or rule out the initial findings. This approach ensures accurate diagnosis and prevents unnecessary treatment or anxiety.
Important Considerations
The information here is for educational purposes only and is not a substitute for professional medical advice. Always consult with a healthcare provider for proper interpretation of test results and any necessary follow-up testing.
