How does Mycoplasma infection affect Antineutrophil Cytoplasmic Antibody (ANCA) test results?

Mycoplasma Infection Can Cause False Positive ANCA Test Results

Mycoplasma infections can cause false positive ANCA test results, particularly P-ANCA patterns, which may lead to misdiagnosis of ANCA-associated vasculitis if clinical correlation is not carefully performed. 1, 2

Understanding ANCA Testing and Interpretation

• ANCA testing should be performed using high-quality antigen-specific assays for both PR3-ANCA and MPO-ANCA as the primary method of testing in patients with suspected vasculitis 1
• The diagnosis of ANCA-associated vasculitis should never be made on ANCA serology alone, as ANCA can be found in other inflammatory diseases, infections (including mycoplasma), and can be drug-induced 1
• If immunoassay is negative but clinical suspicion remains high, a second test (either another immunoassay or indirect immunofluorescence) is advised 1
• The 2017 international consensus statement recommends high-quality immunoassays for PR3 and MPO-ANCA as the preferred screening method for diagnosis of ANCA-associated vasculitis 1

Mycoplasma and ANCA: Diagnostic Challenges

• Infections, including mycoplasma, can trigger the production of ANCA, leading to false positive results that may confound diagnosis 2, 3
• P-ANCA patterns (perinuclear staining) are more commonly associated with infectious triggers compared to C-ANCA patterns 1, 3
• When interpreting ANCA results in patients with suspected or confirmed mycoplasma infection, clinicians should consider:
  • The pattern of ANCA positivity (P-ANCA vs C-ANCA) 1
  • The specific antigen target (MPO vs PR3) 1
  • The clinical presentation and whether it aligns with ANCA-associated vasculitis 1, 2

Differentiating Infection-Induced ANCA from True Vasculitis

• True ANCA-associated vasculitis typically presents with:

  • Multi-organ involvement 1
  • Characteristic histopathological findings on biopsy (granulomatous inflammation, necrosis, vasculitis) 1
  • Persistent ANCA positivity even after treatment of infection 2

• Infection-induced ANCA (including mycoplasma) typically:

  • Resolves after successful treatment of the underlying infection 3
  • May not demonstrate the same antigen specificity as seen in true vasculitis 4
  • Often lacks the characteristic histopathological findings of vasculitis on biopsy 1

Recommended Diagnostic Approach

• For patients with positive ANCA and suspected infection:

  • Confirm ANCA positivity using both indirect immunofluorescence (IIF) and enzyme-linked immunosorbent assay (ELISA) 3
  • Test for specific antigens (MPO and PR3) to improve specificity 1
  • Consider testing for mycoplasma and other infectious agents 2
  • Obtain tissue biopsy from affected organs when possible to confirm or exclude vasculitis 1

• Samples should be considered truly ANCA positive only when they test positive on both IIF and ELISA, which reduces false positives 3

Clinical Implications and Management

• In patients with confirmed mycoplasma infection and positive ANCA:

  • Treat the underlying infection first 2
  • Reassess ANCA status after resolution of infection 3
  • Reserve immunosuppressive therapy for cases with definitive evidence of vasculitis 1

• False positive ANCA results due to mycoplasma can lead to unnecessary and potentially harmful immunosuppressive treatment if misdiagnosed as vasculitis 1, 2

Monitoring and Follow-up

• Sequential monitoring of ANCA titers can be useful in distinguishing infection-induced ANCA from true vasculitis 2
• In infection-induced ANCA, titers typically decrease or disappear after successful treatment of the infection 3
• In true ANCA-associated vasculitis, titers may correlate with disease activity and can be useful for monitoring disease course 2