What could cause a false positive Antinuclear Antibody (ANA) test result with a negative Rheumatoid Arthritis (RA) test result?

Causes of Positive ANA with Negative Rheumatoid Factor

A positive ANA with negative RF is not a "false positive" but rather reflects different antibody profiles that occur in distinct clinical contexts—this pattern is commonly seen in healthy individuals, infections, non-rheumatic conditions, and various autoimmune diseases other than rheumatoid arthritis.

Understanding the Clinical Significance

The key misconception here is terminology: a positive ANA with negative RF is not a "false positive" for ANA—it's a true positive ANA that simply indicates you're not dealing with rheumatoid arthritis. These are two completely different antibody systems:

• ANA positivity occurs in 31.7% of healthy individuals at 1:40 dilution, 13.3% at 1:80, and 5.0% at 1:160, making low-titer results particularly common in people without disease 1
• RF is specific for rheumatoid arthritis and related conditions, while ANA screens for a broad range of autoimmune diseases, particularly systemic lupus erythematosus, Sjögren's syndrome, and systemic sclerosis 1
• The two tests measure fundamentally different antibodies and are not expected to correlate unless a patient has overlapping autoimmune conditions 2

Common Causes of Positive ANA with Negative RF

Healthy Individuals (Most Common)

• Up to one-third of healthy people test positive for ANA at low titers (1:40), with prevalence decreasing as titers increase 1
• ANA positivity is more common in women and elderly populations even without any disease 3
• The ANA test is highly sensitive but not specific, meaning many positive results occur in people who will never develop autoimmune disease 4, 5

Infectious Diseases

• Mycobacterium tuberculosis is the most common infectious cause of positive ANA (10 out of 43 confirmed infections in one study) 6
• Syphilis (Treponema pallidum), scrub typhus (Orientia tsutsugamushi), and E. coli infections frequently produce positive ANA results 6
• Intracellular infections including Bartonella henselae, HIV, and Epstein-Barr virus are associated with ANA positivity 6
• Chronic bacterial or viral infections can trigger low-titer ANA production 3

Non-Rheumatic Medical Conditions

• Hematological malignancies are associated with positive ANA results 3
• Atopic dermatitis and other immune disorders show increased ANA positivity 3
• Various nonrheumatic diseases and conditions can cause positive ANA without any connection to rheumatoid arthritis 4

Drug-Induced and Environmental Factors

• Certain medications and xenobiotics can trigger autoantibody production and positive ANA 3
• Vitamin D deficiency correlates with ANA occurrence in patient populations 3

Other Autoimmune Diseases (ANA-Positive, RF-Negative)

• Systemic lupus erythematosus (SLE) is the classic ANA-positive, RF-negative disease 1
• Sjögren's syndrome, systemic sclerosis, and mixed connective tissue disease typically present with positive ANA but negative RF 1
• Inflammatory myopathies show ANA positivity without RF 1

Technical and Laboratory Considerations

Method-Related Issues

• Different ANA testing platforms (immunofluorescence vs. solid phase assays) have different performance characteristics, which can affect results 1
• The choice of testing method should always be specified on laboratory reports, as results may vary between platforms 1
• Poor specimen collection and handling can affect test accuracy, though this would cause false negatives rather than false positives 2

Immunosuppression Effects

• Patients on immunosuppressive therapy may have suppressed RF production while still maintaining ANA positivity 2
• Immunocompromised states including renal failure can affect serologic results, potentially causing false negative RF while ANA remains positive 2

Critical Clinical Approach

When to Pursue Further Testing

• If ANA titer is ≥1:160, specific antibody testing should always be pursued regardless of RF status, as this titer has 86.2% specificity and 95.8% sensitivity for systemic autoimmune diseases 1
• Order extractable nuclear antigen (ENA) panel including anti-Sm, anti-RNP, anti-SSA/Ro, anti-SSB/La, anti-Scl-70, and anti-Jo-1 when ANA is positive at significant titers 1
• Anti-dsDNA testing is mandatory for homogeneous ANA patterns using both CLIFT and solid phase assays 1

Common Pitfalls to Avoid

• Never diagnose autoimmune disease based on ANA alone—you must have compatible clinical symptoms, laboratory abnormalities, and positive disease-specific autoantibodies 1
• Do not order ANA testing in patients with vague complaints or symptoms—it should only be used when signs or symptoms of rheumatic disease are present 4
• Avoid simultaneous ANA and ENA testing during initial screening—stepwise addition of ENA when ANA is positive is more appropriate, as the yield of newly diagnosed disease with negative ANA but positive ENA is only 6.09% 7
• Do not repeat ANA testing for monitoring once a diagnosis is established—ANA is intended for diagnostic purposes only 1

Risk Stratification by Titer

• At 1:40-1:80, exercise great caution in interpretation as these titers have low positive likelihood ratios and may represent normal variation 1
• At ≥1:160, the positive likelihood ratio is substantially higher and warrants systematic evaluation even in asymptomatic patients 1, 8
• Consider testing anti-SSA/Ro specifically even at titers between 1:80-1:160, as this antigen can be clinically important 1