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Common Test-Ordering Errors
Part 6: Overordered Microbiology Tests

HIV-Qualitative & Quantitative (Same Order)
Serum Bacterial Antigen



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Bacterial Antigen Testing Limitations

Slide 9

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.

Bacterial Antigen Testing Limitations

 


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