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Common Test-Ordering Errors
Part 6: Overordered Microbiology Tests

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

Click CC box for captions; full transcript is below.

Published: September 2010

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Dr. Dale reviews test-ordering errors commonly seen at Mayo Medical Laboratories. This is the sixth presentation in the series and addresses overordered tests including HIV and serum bacterial antigen testing.

Presenter: Jane C. Dale, MD of the Division of Laboratory Medicine and Pathology

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Welcome to Mayo Medical Laboratories' Hot Topics. These presentations provide short discussions of current topics and may be helpful to you in your practice.

Our presenter for this 8-part series is Dr. Jane Dale, a consultant in the Department of Laboratory Medicine and Pathology at Mayo Clinic. Dr. Dale reviews test-ordering errors commonly seen at Mayo Medical Laboratories. This is the sixth presentation in the series and addresses overordered tests including HIV and serum bacterial antigen testing.

Testing at Mayo Medical Laboratories

Here at Mayo Medical Laboratories we receive over 800,000 test orders each month. While by our estimation most of the orders we receive are appropriate orders, we do experience some recurring test-ordering problems. In this presentation, I will describe the most common problems that we see. I will also describe our efforts to decrease these problems and recommend ways that you too can help reduce these errors. Together, by decreasing inappropriate test orders, we can improve patient care and reduce costs.

In this 8-part series, I will address 2 types of errors—misordered tests and overordered tests.

Common Microbiology Test-Ordering Problems

In parts 1 through 3, I addressed the most commonly misordered tests. In parts 4 and 5, I addressed a number of the overordered tests. In parts 6 through 8, I will shift my focus to overordered microbiology tests, which are shown on this slide. Today, I will address the first 2 bullet items—HIV testing and bacterial antigen testing.

HIV Qualitative & Quantitative; Both Ordered

At Mayo Medical Laboratories, we do a lot of HIV testing and one problem that we encounter is that we often receive requests, on a single patient, for both the quantitative HIV test, as well as the reflex test that first quantitates HIV levels and then reflexes results >1,000 copies/mL to HIV genotyping. Genotyping is used to help physicians know if a patient is likely to be susceptible to standard drugs. We are not sure why this particular duplicate order occurs so frequently, especially since our test catalog indicates 3 options: Quantitative viral levels, Genotyping, and Quantitative and genotyping together.

Our accessioning team screens these orders and when these tests are ordered together, we cancel 1 of the tests and perform the reflex test, sparing the patient the charge for the duplicate order. You can do your part by understanding the components of reflex tests and making sure that redundant orders are not passed on.

Bacterial Antigen Testing

Serum bacterial antigen tests are another misordered test, one that we believe should not be used. Bacterial antigen testing was developed to aid in the diagnosis of meningitis, a disorder that can be of either infectious or noninfectious origin. Most cases of infectious meningitis are caused by viruses (this was previously called aseptic meningitis because routine cerebrospinal fluid [CSF] bacterial cultures yielded no growth). While most meningeal infections are viral, bacterial causes are not uncommon. Differentiating viral from bacterial causes of meningitis is important because they are treated differently. Bacterial infections require prompt antibiotic therapy to avoid serious and sometimes fatal outcomes. In contrast, supportive care (and perhaps antiviral therapy) is indicated for patients with viral meningitis. Bacterial antigen testing offered the benefit of being faster than culture.

Diagnosing Bacterial Meningitis

Nonmicrobiologic CSF tests (such as cell counts, protein, and glucose) cannot reliably differentiate between bacterial and viral causes of meningitis, and CSF cultures are mandatory in suspected cases. Because culture results are not available for several days, treatment must be initiated before testing is complete. Initial antibiotic selection is made on the basis of Gram stain results or, if the Gram stain is negative, based on well-described empiric treatment protocols. Treatment is modified, if necessary, after culture and antibiotic sensitivity results become available.

Bacterial Antigen Testing

In bacterial antigen testing, reagent antibodies react with antigens contained in bacteria that are common causes of bacterial meningitis (such as, Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, E coli, group B streptococcus). In infected individuals, the antigens may be present in the CSF (for patients with meningitis), in the blood (in the case of sepsis), or in the urine (which can occur in patients with either meningitis or sepsis).

Bacterial Antigen Testing Limitations

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.

Mayo Medical Laboratories Discontinued Serum Bacterial Antigen Testing

Because serum bacterial antigen testing may produce high numbers of false-negative and false-positive results, relying on serum bacterial antigen results constitutes substandard patient care and the use of bacterial antigen testing in conjunction with other diagnostics tests represents, at best, an unnecessary expense that adds little to patient care and, at worst, negatively impacts patient care. Consequently, we discontinued the test and no longer even offer it to our clients.

Testing at Mayo Medical Laboratories

We have similar reservations for bacterial antigen testing performed on CSF and instead recommend Gram stain, culture, and PCR-based viral testing. Mayo Medical Laboratories' "Enterovirus RNA Detection by Rapid Polymerase Chain Reaction (PCR)" is a spinal fluid test that detects the enteroviruses that are the most common causes of meningitis—coxsackievirus, echovirus, and poliovirus—which account for ~80% of cases.


This concludes Part 6 of this series on some of the tests that, in our experience as a reference laboratory, are commonly ordered inappropriately. Please continue to Parts 7 and 8 to complete the section on overordered microbiology tests.