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Does a Positive Herpes IgM Test Mean I Was Recently Infected with Herpes?

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Updated May 29, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

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Question: Does a Positive Herpes IgM Test Mean I Was Recently Infected with Herpes?
Answer:

Many doctors will tell patients with a positive herpes IgM test that their test results mean they were recently infected with herpes. This is because herpes IgM antibodies, and IgM antibodies generally, are thought to peak shortly after an initial infection and then recede. In contrast, herpes IgG antibodies develop more slowly, but they are expected to remain high throughout the course of an infection.

Recent research, however, suggests that the common wisdom about herpes blood test results may not be accurate. Although individuals who were recently infected with herpes do tend to have positive herpes IgM tests, so do many people with recurrent herpes infections -- between 30 and 70 percent of them depending on the test and the study.

Herpes IgM tests are more likely to be positive in early herpes infections than herpes IgG tests, but a positive herpes IgM test alone is not a reliable marker that an infection is recent - particularly if it is accompanied by a positive herpes IgG test.

If you have a positive herpes IgM test with a negative herpes IgG test, then it is more likely that your results correctly signal a recent infection. However, to avoid possibly misinterpreting false positive test results, if you have no symptoms, you may want to go back for IgG testing at a later date. If you do have symptoms, your doctor can test the lesions for herpes directly, without the need to wait for an antibody response.

Detectable levels of herpes IgG take longer to develop than detectable levels of herpes IgM. However, even herpes IgM antibodies can take up to ten days to develop after primary infection with the virus. If you believe you have been exposed, but have no symptoms, you should therefore wait at least two weeks before getting tested - or even longer, depending on which tests are available in your area. You may also want to go for a repeat test after 6 months if you do not undergo regular screening.

Sources:

Hashido M, Kawana T. "Herpes simplex virus-specific IgM, IgA and IgG subclass antibody responses in primary and nonprimary genital herpes patients." Microbiol Immunol. 1997;41(5):415-20.

Ho DW, Field PR, Sjögren-Jansson E, Jeansson S, Cunningham AL. "Indirect ELISA for the detection of HSV-2 specific IgG and IgM antibodies with glycoprotein G (gG-2)." J Virol Methods. 1992 Mar;36(3):249-64.

Morrow, R. and Friedrich, D. "Performance of a novel test for IgM and IgG antibodies in subjects with culture-documented genital herpes simplex virus-1 or -2 infection" Clin Microbiol Infect 2006; 12: 463–469

Page J, Taylor J, Tideman RL, Seifert C, Marks C, Cunningham A, Mindel A. "Is HSV serology useful for the management of first episode genital herpes?" Sex Transm Infect. 2003 Aug;79(4):276-9.

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