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Common Test-Ordering Errors
Part 7: Overordered Microbiology Tests

Helicobacter pylori IgM
Stool Ova & Parasites

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Published: October 2010

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Dr. Dale reviews test-ordering errors commonly seen at Mayo Medical Laboratories. This is the seventh presentation in the series and addresses overordered tests including Helicobacter pylori IgM and stool ova and parasites.

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.

Common Mayo Medical Laboratories Test-Ordering Errors

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

Common Microbiology Test-Ordering Problems

In part 6, I started a review of common test-ordering problems with microbiology tests, covering the first 2 bullet items. In part 7, I will address Helicobacter pylori and stool parasite tests.

Helicobacter pylori

Helicobacter pylori is a causative agent of chronic active gastritis, duodenal ulcer, and nonulcer dyspepsia. The serology test for Helicobacter pylori, especially IgM, is overordered, in the opinion of our microbiologists and infectious disease physicians. A number of methods are available for the diagnosis of Helicobacter pylori infection. In addition to the available serologic tests (IgG, IgM, and IgA), H pylori tests include the stool antigen test, the urea breath test, and tests performed on biopsy specimens obtained by endoscopy. The tissue tests include culture, microscopic examination and direct urease testing (also referred to as the CLO test). Each of these tests has its drawbacks, including, for serology—lack of specificity, or for the breath test and endoscopy—high cost and complexity, and inconvenience for the patient.

H pylori IgM (and IgA) Not Useful

Regarding serology tests, because H pylori is a chronic infection, by the time symptoms occur, the infection has been present for some time and, therefore, IgG is consistently positive. Furthermore, a negative IgM does not rule-out active infection. That is, patients with active infection can have negative IgM results. Also, IgM levels should not be used as a test of cure, as the IgM may remain positive despite eradication of the organisms. Consequently, the use of IgM (or IgA for that matter) adds little to the assessment.

H pylori Diagnostic Algorithm

Mayo’s recommend approach is described in a diagnostic algorithm that is available on our web site and in our electronic test catalog (where it can be scaled up for easier viewing). The algorithm describes approaches based on the patient’s symptoms and age.

The basics of the approach are as follows—for patients with worrisome symptoms (that is, tarry stools, bloody vomit, anemia, weight loss, and/or difficulty swallowing) the preferred first test is endoscopy. This is recommended because it is the best way to most accurately assess patients and not miss serious disorders. For adults who do not have those symptoms, the preferred test is the urea breath test or the fecal antigen test. For children who do not have those symptoms, because the urea breath test can be difficult to administer to children, the preferred first test is the fecal antigen test. In both age groups, IgG serology testing is an optional alternate testing choice, but IgM and IgA are not recommended.

Ova and Parasite

Another overordered test is the examination of stool for ova and parasites. O & Ps are the traditional method to identify gastrointestinal parasites. The test involves microscopic examination of specially prepared fecal samples by highly trained and experienced technologists. Although appropriate for identifying many exotic parasites, the O & P procedure actually is a less sensitive method for detecting the most common fecal parasites in the United States, namely Giardia intestinalis (also known as Giardia lamblia or Giardia duodenalis) and Cryptosporidia species. These parasites may be suspected when patients present with watery diarrhea and have a supportive exposure history. In that setting, newer ELISA tests for Giardia and Cryptosporidium are more sensitive, can be performed more quickly, and are more cost-effective initial tests.

Parasitic Investigation of Stool Specimens Algorithm

We have developed a diagnostic algorithm for Parasitic Investigation of Stool Specimens. We also have a Hot Topic video on this topic that viewers can watch on our web site.

Initial Testing in Patients with Watery Diarrhea

In brief, for patients with watery diarrhea who have AIDS, have contact with farm animals, or are involved in an outbreak in a municipal water supply, Cryptosporidium antigen testing is recommended as the first test. For patients with watery diarrhea who are ≤5 years old (or their contacts), are campers, or who are involved in outbreaks in resort communities, Giardia antigen testing is recommended. In patients with watery diarrhea who are involved in daycare outbreaks, both Crypto and Giardia antigen testing are recommended. Traditional O & P is reserved for patients who are residents or visitors to developing countries or to areas of North America where infections caused by worms are reported with some frequency. We believe that, by following this approach, unnecessary O & P tests can be significantly reduced.


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