WHAT DOES A POSITIVE HERPES IgM TEST RESULT MEAN?
Question: Does a Positive Herpes IgM Test Mean I Was Recently Infected with Herpes?
Many doctors will tell patients with a positive herpes IgM test that their test result means they were recently infected with herpes (HSV). This is because HSV IgM antibodies are thought to peak shortly after an initial infection and then recede. In fact, that is the common wisdom for IgM antibodies in general.
Compared to IgM, herpes IgG antibodies develop more slowly. However, they are expected to remain high throughout the course of an infection.Therefore, a positive HSV IgG test is thought to mean that the detected infection is at least several months old.
Interestingly, recent research suggests that the common wisdom about herpes blood test results may not be accurate. Individuals who were recently infected with herpes DO tend to have positive HSV IgM tests. However, so do many people with recurrent herpes infections. Between 30 and 70 percent of people with recurrent herpes are positive on HSV IgM tests, depending on the test and the study.
Herpes IgM tests are more likely to be positive in early herpes infections than herpes IgG tests. All this shows is that a positive herpes IgM test alone does not prove that an infection is recent. That's particularly true if it is accompanied by a positive herpes IgG test.
If you have a positive herpes IgM test and a negative herpes IgG test, then it is more likely that your results signal a recent infection. However, it is possible to misinterpret false positive test results. Therefore, 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. There is no 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. Therefore, if you believe you have been exposed but have no symptoms, don't run to the doctor. It's best to 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.
WHAT DOES A POSITIVE HERPES IgG TEST RESULT MEAN?
Herpes IgG tests are one type of blood test for the herpes simplex virus (HSV). Herpes blood tests look for the body's immune reaction to a herpes infection. They don't search directly for the virus. Because the immune reaction takes time to develop after the time of infection, it's not immediately detectable. In fact, depending on the type of test used, it can take up to four months to become positive on an HSV IgG test.
How Does an HSV IgG Test Work?
When a person becomes infected,the immune system tries to fight off the infection. That's true not just for herpes but for any pathogen, Part of that process involves the production of antibodies. These proteins are specific for each infection they are fighting.
For a new type of infection, it takes time for the body to make strong antibodies. The body can make several kinds of antibodies to fight infections. The two types that herpes blood tests look for are IgG and IgM. Herpes IgM antibodies usually are detectable by herpes blood tests within 7-10 days after initial infection. IgM levels stay high for approximately two weeks. After that, they usually decline.
Therefore IgM testing is primarily considered to be useful for detecting acute infection. However antibody levels also sometimes go up during an outbreak.
In contrast, herpes IgG antibodies do not show up until slightly later after initial infection. A positive herpes IgG test, if the test result is accurate, means that your body has been infected with the herpes simplex virus.
Furthermore, type specific herpes IgG tests can be used to distinguish between HSV-1 and HSV-2. Type-specific tests are far more accurate than non type-specific tests,However, they can not detect whether a particular infection is oral or genital. The only way to determine that is to watch for symptoms.
HSV-1 usually infects the mouth, causing oral herpes, and HSV-2 usually infects the genitals. However, there are a growing number of people with genital HSV-1. That's why herpes IgG and IgM tests can only tell you that you have been infected. They can't show where where.
HSV Blood Test Results & Timing of Infection
If you test positive for herpes IgG but not IgM, then your herpes infection is probably not recent. You've probably been infected for at least two months. Individuals with newer infections are more likely to test positive for both herpes IgG and IgM. They might also be positive for herpes IgM alone. The converse, however, isn't true. Positive herpes IgG and IgM results together do not necessarily mean you were infected recently. Between 30 and 70 percent of patients with recurrent herpes infections will test positive for herpes IgM.
| || Positive IgG||Negative IgG|
|Positive IgM|| Infection date indeterminate|| Acute/Recent infection|
|Negative IgM|| Established Infection|| No infection detected|
It is possible to have a false positive or false negative result. That's true for either a HSV IgG or HSV IgM test. Therefore, don't panic if your herpes blood test results do not agree with your known risk factors and sexual history. Instead, talk to your doctor about possible issues with testing. Diagnostic testing isn't perfect. You also may not be accurately assessing your risk. Many people do not understand that herpes can be transmitted even when their partner has no symptoms or does not know they are infected.
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, 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 May;12(5):463-9.
Morrow RA, Friedrich D. Inaccuracy of certain commercial enzyme immunoassays in diagnosing genital infections with herpes simplex virus types 1 or 2. Am J Clin Pathol. 2003 Dec;120(6):839-44.
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.
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.