Common Test-Ordering Errors
Part 6: Overordered Microbiology Tests

Bacterial Antigen Testing Limitations

September 2010

While serum bacterial antigen testing provides theoretical advantages, in practice it has major limitations including:

• This test shows poor specificity.
• False-positive results are common (causes include contamination with skin flora and the presence other infections with cross-reacting organisms).
• This test shows poor sensitivity.
• It is rarely positive when Gram stains or cultures are negative.
• The test has no advantages over Gram stain.
• This test cannot replace culture, and
• This test should not be used to direct or modify treatment.

Because serum bacterial antigen testing offers no advantages over Gram stain, performing these tests represents an unnecessary expense. While the direct cost of testing is modest, indirect costs can be significant. False-positive results may lead to unnecessary antibiotic treatment, prolonged hospital stays (with the attendant risk of complications), and increased laboratory testing and specialty consultations. One study showed a cost of approximately $8000 (in 1995 dollars) for each positive result with no demonstrable clinical benefit.

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Jump to section:

• Introduction
• Testing at Mayo Medical Laboratories
• Common MML Test-Ordering Errors
• Common Microbiology Test-Ordering Problems
• HIV Qualitative & Quantitative; Both Ordered
• Bacterial Antigen Testing
• Diagnosing Bacterial Meningitis
• Bacterial Antigen Testing
• Bacterial Antigen Testing Limitations
• MML Discontinued Serum Bacterial Antigen Testing
• Diagnosis of Meningitis
• Conclusion
• Questions?