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

The answer depends on what type of herpes test is used

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Genital herpes is one of the most stigmatized STDs. Because of that, exposure to the virus can cause a lot anxiety for people. That makes it very important to understand the limitations of herpes blood tests. That includes not just their accuracy but how long they take to become effective. 

Why Use Herpes Blood Tests?

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. It just means that they may never know that they've become infected without a positive herpes blood test. 

Herpes tests aren't perfect. However, because so many people with herpes don't have symptoms, these tests 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 antibodies aren't produced immediately after infection. Therefore, people often wonder how long it takes for a herpes test to be accurate. The simple answer is that it depends on the test. 

The longer answer is that there isn't a clear answer. 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. In order to do that, people would have to know both that they had been infected and when the infection occurred.

If a person is asymptomatic, neither piece of information is available.

In such cases, there is no way to tell a person is 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.

Tests That Show the Herpes Virus

If 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, not 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. So, how long does it take for a genital herpes blood test to become positive after exposure? It varies depending on the type of 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. 
  • Western Blot - 40 days for people who were HSV-1 negative and 47 days for those who were HSV-1 positive. 
  • Western Blot - 68 days. 
  • Kalon ELISA - 120 days. 
  • Focus ELISA - 21 days. 

The truth is, it's usually even longer than those numbers above. Remember, it usually takes around two 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. It's also important to remember that the numbers  provided above are for people who have had symptoms. Scientists have no clear way to know if the time to a positive test is shorter or longer for those people who are infected without  symptoms developing. 

Sources:

The CDC Genital Herpes Fact Sheet. http://www.cdc.gov/std/Herpes/STDFact-Herpes.htm Updated May, 2016

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