Common Test-Ordering Errors
Part 8: Overordered Microbiology Tests
Mumps, Measles and Varicella Serologies
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.
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