Hot Topic

Common Test-Ordering Errors
Part 8: Overordered Microbiology Tests

Mumps, Measles and Varicella Serologies
Lyme Serology


Receive notification when new Hot Topics are published:

Click CC to turn on closed captioning.

Published: November 2010

Print Record of Viewing

The final presentation in an 8-part series on commonly seen test-ordering errors. Part 8 addresses continues the discussion of overordered microbiology testing.

Presenter: Jane C. Dale, MD

Questions and Feedback

Contact us:



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 final presentation in the series and continues the discussion of overordered microbiology tests, this time focusing on serology tests for mumps, measles, varicella, syphilis, and Lyme disease.

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 address 2 types of errors—misordered tests and overordered tests.

Common Microbiology Test-Ordering Problems

In this, the final presentation in this series, I will complete the discussion of common test-ordering problems with the microbiology tests, focusing on serology testing.

IgG and IgM, When IgG Answers Clinical Question

Serology testing is problematic, particularly orders for both IgG and IgM, when one alone would answer the clinical questions. This is most notable for rubella, mumps, measles, and varicella. Through client investigations, we know that we receive many orders for both IgM and IgG serologies for these viruses when IgG alone would suffice. In most instances, the physician only wants to know if the patient has responded to an immunization. IgG is the test for this purpose, and ordering IgM, which is indicated for identifying acute infection, not only represents an additional, unnecessary expense, it can have major downstream consequences for the physician, patient, and the laboratory. These adverse consequences are especially true for rubella.


Let me expand upon that point. Rubella (also called German measles or 3 – day measles) is typically a rather mild disease. But, when rubella is contracted by a woman during pregnancy, it can have very serious effects on the developing fetus including life-threatening birth defects. Thankfully, due to an effective immunization program implemented in the late 1960s, rubella is now extremely rare in the United States. But, because the incidence of the disease is so low, the positive predictive value of the IgM test for acute rubella is also very low. This means that in the United States, almost all positive rubella IgMs are false-positives—not something of which all caregivers are aware.

Consequently, Mayo has discontinued the rubella IgM test. This eliminates the potential adverse consequences of a false-positive rubella IgM result including unnecessary patient anxiety and termination of the pregnancy decisions. If a case of suspected rubella infection should occur, we recommend that you contact your local state health department or the CDC, who have the resources to investigate the situation. For further information on this, listen to our Hot Topic on rubella. Similarly, for mumps, measles and varicella, in most cases, the physician only wants to determine a vaccination or exposure history, which is shown by the IgG results. When both IgM and IgG are ordered, we often find false-positive IgMs, which cause problems for the patient and the physician. We also have similar issues with syphilis IgM and IgG being ordered on pregnant women.

When your receive orders for both IgG and IgM for the infectious diseases rubella, measles, mumps, varicella, and syphilis, you might be able to eliminate the problems mentioned, and reduce costs, by proactively contacting the ordering provider to see if he or she is only looking to document previous exposure or immunity and, if so, suggesting that the order for IgM be canceled.

Lyme Disease Testing

Finally, I would like to address Lyme disease serology tests. Lyme disease is a tick-borne illness that is endemic in certain areas of the United States. It is caused by the spirochete Borrelia burgdorferi. In most people, the tick bite results in inflammation of the skin around the area of the bite, creating a unique expanding, ring-like skin lesion. This lesion is called erythema migrans and is an indicator of the first stage of Lyme disease.


According to the CDC, Lyme disease is diagnosed based a history of possible exposure to infected ticks, on symptoms, and objective physical findings (including erythema migrans, facial palsy, or arthritis).

Lyme Serology

When a patient has erythema migrans, laboratory tests are not generally recommended. In the context of tick exposure, the presence of erythema migrans is diagnostic in itself and patients do not require laboratory testing. Furthermore, since EIA screening tests are insufficiently sensitive in early stage disease (sensitivity is approximately 75% early in the disease), a false-negative result can occur, which would complicate the diagnostic process. Additionally, because Lyme serologies may also yield false-positive results (for example, IgM western blotting only requires 2 bands to be positive and 1 band can cross react with common urinary pathogens), the test should only be ordered in patients with symptoms and a high likelihood of a tick bite. Indiscriminate testing can result in a diagnostic dilemma and lots of confusion on the part of both physician and the patient. For additional information, I would refer you to Mayo Medical Laboratories' Hot Topic on Lyme disease.


This concludes this series on some of the tests that, in our experience as a reference laboratory, are commonly ordered inappropriately. While each of you may find a different set of tests that fall into this category, it is my hope that by periodically reviewing test appropriateness, we can all find ways to improve. Some improvements require education, whereas others require procedural or systematic solutions. Some solutions are best addressed by those ordering the tests, whereas others are best addressed by those performing the test. We look forward to hearing from you about ways that we at Mayo Medical Laboratories can help reduce test-ordering errors, as well as ways that you have found to do the same, striving to always assure that the right test is ordered, on the right patient, at the right time. The algorithms and Hot Topic presentations referenced by me are available at You can also access issues of the Communiqué and our test catalog. For your convenience, I've listed our customer service phone number.