How Long Do I Have to Wait Before a Herpes Blood Test is Effective?

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Question: How long do I have to wait before a herpes blood test is accurate?

Most people who will become symptomatic with genital herpes start showing symptoms within two weeks of exposure to the virus. However, the vast majority of people with herpes will never have symptoms at all. That doesn't mean that they can't still transmit the genital herpes virus.

Even if herpes tests aren't perfect, they are often the only way to know if you are infected.

The problem is that many herpes blood tests look for antibodies to the virus. Those are not produced right away. The question is this: How long does it take for a herpes test to be accurate? 

Answer: It can take several months

If the symptoms are present, it is easy for a doctor to diagnose a herpes infection. They can either simply examine the outbreak or swab the sores for the herpes virus. However, it can be harder to determine if someone is sub-clinically infected . In other words, to determine if they are infected but have no obvious symptoms. To find these patients, doctors need to do a herpes blood test.

Blood tests for HSV-2, the virus that is most often associated with genital herpes, generally look for present antibodies to the virus.They don't look for  the virus itself. Unfortunately, it takes some time for the body to mount a detectable antibody response after infection. That's why you can't simply go get tested the day after you've been exposed to genital herpes.

The test wouldn't be accurate. Even if you were infected, at that point there's no way for the test to pick it up. So, how long does it take for a genital herpes blood test to become positive after exposure? The answer is that it depends on the test.

Various studies have investigated how long it takes from when genital herpes symptoms show up to when an individual tests positive on a blood test for HSV-2.

As it turns out, the range varies a great deal. This is true both between studies and between tests. For example, the median time from symptoms to a positive HSV-2 blood test was:

  • HerpeSelect ELISA - 21 days for people who were HSV-1 negative and 23 days for people who were HSV-1 positive. (Ashley-Morrow et al. 2003)
  • Western Blot - 40 days for people who were HSV-1 negative and 47 days for those who were HSV-1 positive. (Ashley-Morrow et al. 2003)
  • Western Blot - 68 days. (Morrow et al. 2003)
  • Kalon ELISA - 120 days. (Morrow et al 2003)
  • Focus ELISA - 21 days. (Morrow et al 2003)

The truth is, it's even longer than those numbers above. Remember, it usually takes around 2 weeks for symptoms to show up. Therefore, it's probably a good idea to wait at least a month or two before even considering getting an HSV-2 test after a potential exposure . Even then, you might want to consider getting retested after six months. Remember, after all, that those are only median times and that they were highly variable.

Some infected people will seroconvert quickly. Others will take even longer before a herpes blood test accurately shows them to be positive.

Note: There is no practical way for researchers to directly answer the question of how long it takes for a positive test to show up in asymptomatic people. You'd have to know both that they had been infected and when they had become infected. If a person is asymptomatic, neither piece of information is available. After all, there is no way to tell they are infected until they test positive. The assumption is that the time course of a positive genital herpes blood test is similar to that seen in symptomatic individuals. However, that assumption is difficult to verify. Most asymptomatic individuals who eventually test positive do not know exactly when they were exposed.

Sources:

Ashley-Morrow R, Krantz E, Wald A. Time course of seroconversion by HerpeSelect ELISA after the acquisition of genital herpes simplex virus type 1 (HSV-1) or HSV-2. Sex Transm Dis. 2003 Apr;30(4):310-4.

Morrow RA, Friedrich D, Krantz E. Performance of the focus and Kalon enzyme-linked immunosorbent assays for antibodies to herpes simplex virus type 2 glycoprotein G in culture-documented cases of genital herpes. J Clin Microbiol. 2003 Nov;41(11):5212-4.

The CDC Genital Herpes Fact Sheet. http://www.cdc.gov/std/Herpes/STDFact-Herpes.htm

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