Can Influenza Cause a False Positive ANA Test?
Yes, influenza and other acute viral infections can cause false positive ANA test results, though this phenomenon is more commonly documented with chronic infections rather than acute flu specifically.
Understanding the Relationship Between Infections and ANA Positivity
The connection between infections and positive ANA tests is well-established in the medical literature. Positive ANA results may occur with both acute and chronic infections, not just autoimmune diseases 1. This is particularly important when ANA testing is used as an initial screen in patients presenting with non-specific symptoms like fever, joint pain, myalgias, fatigue, or rash—symptoms that overlap significantly with influenza 1.
Key Mechanisms and Clinical Context
Infections trigger immune responses that can produce autoantibodies temporarily, including antinuclear antibodies, as part of the body's inflammatory response 1, 2.
The ANA test is highly sensitive but not specific, meaning many non-rheumatic diseases and conditions can cause positive results, and some healthy persons have positive results even without any disease 3.
Low-titer ANA positivity is found in the course of chronic bacterial or viral infections, though the literature more commonly documents this with chronic rather than acute viral illnesses 2.
Clinical Implications for Influenza Patients
When to Suspect False Positive Results
If a patient presents with typical influenza symptoms (fever, respiratory symptoms, myalgias) and has a positive ANA, consider that the ANA positivity may be infection-related rather than indicative of autoimmune disease 1, 4.
The relatively high prevalence of ANAs in inflammatory conditions makes a positive result difficult to interpret in the acute infection setting 4.
Important Caveats
ANA testing should not be used to evaluate patients who have vague complaints or non-specific symptoms 3. If a patient has clear influenza symptoms, ANA testing is generally not indicated unless there are specific signs or symptoms suggesting underlying rheumatic disease.
The ANA result itself has no diagnostic value without appropriate clinical context, especially considering the possibility of false positives from infections, medications, and other factors 2.
False positive results can also occur due to the choice of method used to determine antibodies, so technical factors must be considered 2.
Practical Approach
If you encounter a positive ANA in a patient with acute influenza:
Do not immediately pursue extensive autoimmune workup during the acute illness 1, 3.
Consider repeating the ANA test 8-12 weeks after resolution of the acute infection to determine if the positivity was transient and infection-related 1, 2.
Only pursue further specific autoimmune investigation if the patient has clinical signs or symptoms of rheumatic disease beyond the acute viral illness 3.
Remember that ANA positivity is more common in women and the elderly, populations also at higher risk for influenza complications 2.