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Serology Testing for Rubella IgM Discontinued


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July 2008

Rubella is a contagious viral infection often referred to as 3-day or German measles (not to be confused with classic measles, which is caused by the rubeola virus). In 2005, the Centers for Disease Control and Prevention (CDC) announced the absence of endemic transmission of rubella in the United States, largely due to successful vaccination programs.1 Fewer than 10 cases of rubella were reported in 2004, and the majority of those cases occurred in individuals born outside the United States. The incidence of congenital rubella syndrome (CRS)–a syndrome that results from maternal infection during the first trimester, affecting the developing fetus–has also been significantly reduced, with a total of 4 cases of CRS reported to the CDC during 2001-2004.

Serologic testing for rubella has commonly included testing for either, or both, IgM- and IgG-class antibodies. The determination of immune status to rubella by serologic testing for IgG-class antibodies to this virus is very useful information, particularly for women of child-bearing age. However, given the low prevalence of rubella in the United States, IgM testing for the laboratory assessment of acute rubella infection is of limited clinical value and may yield false-positive results, which can negatively impact patient care, as noted below:

“…In the absence or near absence of disease, serologic assays, even those with very high specificity (>99%), can result in virtually all positive test results being falsely positive.

It is important to note that many of the tests for acute rubella—for example, IgM tests—were likely performed prenatally. Although not recommended, this still-common practice among obstretical [sic] health care providers in the United States leads to numerous false-positive test results.

…Continuing to screen asymptomatic pregnant women by use of IgM testing may result in substantial anguish to the parent, needless expenditure of resources, and possible termination of healthy pregnancies.2

For these reasons, effective July 1, 2 008, Mayo Clinic has discontinued all testing for IgM-class antibodies to rubella and will no longer offer the following tests:

  • #83264 Rubella Antibodies, IgG and IgM, Serum
  • #8317 Rubella Antibodies, IgM, Serum
  • #80804 (rubella component only) TORCH Profile IgM

Additionally, because of the significant negative impact of a false-positive test result, Mayo Medical Laboratories will no longer forward specimens for rubella IgM-class antibody testing.

IgG-class antibody testing to demonstrate immunity to rubella will remain available:

  • Rochester: #8172 Rubella Antibodies, IgG, Serum
  • New England: #110021 Rubella Antibodies, IgG, Serum
  • Jacksonville: #800070 Rubella Antibodies, IgG, Serum

If acute rubella or CRS is suspected, it is recommended to communicate directly with your State Health Laboratory or the CDC to arrange appropriate testing and follow-up.

Reference
1. Centers for Disease Control and Prevention: Achievements in Public Health: Elimination of Rubella and Congenital Rubella Syndrome –United States, 1969–2004. MMWR Morb Mortal Wkly Rep 2005 Mar 25;54(11);279-282
2. Averhoff F, Zucker J, Vellozzi C, et al: Adequacy of Surveillance to Detect Endemic Rubella Transmission in the United States. Clin Infect Dis 2006;43:S151-157


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