Testing For Genital Herpes

A guide to help you figure out what is the best way to get tested for genital herpes.

Testing For Genital Herpes
Judy Hsu DO
March 10, 2021, 4:57:07 AM

One of the questions that often come up during my clinical practice is how one can get tested for genital herpes. This is a great question as there are several ways to do this, and which method you pick depends on the scenario that the person is in.

If you are currently experiencing symptoms of genital herpes and have a rash, the most appropriate test to perform is either a viral culture or viral DNA test. Both tests involve breaking one of the herpes lesions open to swab and take a sample of the fluid inside of it. Both can tell which type of herpes virus the person has, whether it is type 1 or type 2. The viral DNA test is usually seen as more superior to viral culture as it is more accurate and sensitive. The problem with the culture is that its accuracy depends on the how many copies of the virus are on the surface that is being swabbed, so if the lesion is small or is on its way to healing, there may not be enough virus to show up on the culture. The accuracy of the culture is even worse when it’s a recurrent infection; only about 30 percent of recurrent outbreaks show up positive. This is why the DNA test is the preferred method of testing for acute active herpes infection. In the clinical setting, the DNA test is often referred to as the PCR test. PCR stands for polymerase chain reaction, and it is one of the methods of nucleic acid amplification testing (NAAT).

If you currently have no symptoms and rash, the way to test for herpes would be to do a blood test since there is no herpes lesion to be swabbed. The blood test does not detect the presence of herpes virus in the body; rather, it is testing for the presence of antibodies to the virus. When a person contracts the virus, the body mounts an immune response to try to get rid of it, and in any kind of immune response to an infection, two types of antibodies are produced: IgM and IgG. IgM is the first type of antibody produced right after an infection, but it peaks quickly and goes away quickly. IgG, on the other hand, gets produced a little later but can stick around for years. Even though sometimes the different levels of these antibodies can help us determine timing of the infection, unfortunately in the case of herpes it is not so straightforward. IgM can reappear during a recurrent outbreak or sometimes even not show up at all even during the initial infection. For thes reasons, IgM and IgG cannot be used to determine timing of the infection in the case of genital herpes.

Blood test for IgM antibodies have two additional major flaws. One is that it cannot reliably distinguish between herpes type 1 and type 2, and because genital herpes is generally caused by type 2 while oral herpes by type 1, if you have a history of cold sores and develped genital rash that happens to be non-herpetic, you might be misled into thinking that you have genital herpes when the IgM test comes back positive. The other down side of IgM test is that it can cross react with others viruses in the same family like chickenpox, so the false positive rate is high.

Blood test for IgG antibodies is in comparison clinically more useful. Unlike IgM, IgG antibodies can be reliably identified as either type 1 or type 2. The only downside is that it does take a while for the body to generate IgG antibodies, sometimes weeks to months, so for this reason, it is generally recommended that this blood test be done 12 weeks after potential exposure.

In summary, if you have active skin lesions suspicious for herpes, the best way to get tested is through a direct swab of the lesion for PCR testing in order to identify the presence of viral DNA. If you have no herpes symptoms but may have been exposed recently, the best test to do is a blood test that detects the presence of IgG antibodies developed against herpes virus. When in doubt, talk to your doctor as he or she will work with you to choose the most appropriate test for the situation.