There is a lot of misinformation about herpes, both among health providers and the general public. When I lecture at a medical conferences about herpes I hear, “I didn’t know that,” all the time. I know people want more information, because I posted a piece in 2011 on the difference between type 1 and type 2 last year and it has over 48,000 hits and counting.

One big area of misunderstanding is blood testing and herpes infections. Blood testing means looking for antibodies. The immune system produces antibodies in response to an infection, and so the presence of antibodies means that at some point there was an infection somewhere with herpes. Now keep in mind that most people with herpes are unaware they have been infected because most people don’t get recurrent cold sores on their lips or genitals, most people have a silent infection and simply periodically shed the virus.

What you need to know about blood testing before you have it:

1) There is only one reliable and commercially available type of blood test for herpes antibodies called a Type Specific IgG. This test can reliably distinguish between herpes 1 and herpes 2 antibodies. There are labs that will run tests that are not type specific, but these are essentially useless. It is unfortunately not illegal to offer a useless test and some providers just don’t know the difference and may just tick off the first box for “herpes” that they see. The University of Washington (the mecca of herpes research) also offers a Western Blot test for herpes antibodies. This is the gold standard, but only performed at the University of Washington. The American Social Health Association has a great guide to the brand names of the reliable tests. If it’s not one of these tests, don’t get it. You may have to ask your health provider to check, because they might not know.

2) Blood tests take 3-6 months to turn positive after exposure because it takes 3-6 months for your body to make IgG antibodies in response to an infection.

3) There is no blood test that can tell you immediate exposure/recent infection. Some less than scrupulous labs and providers might tell you to get an IgM test. IgM antibodies are produced very soon after an infection. If your provider offers an IgM test, get up and leave because they do not know anything about herpes or testing. IgM tests for herpes are highly unreliable for the diagnosis of herpes virus infections and should never be ordered (the FDA doesn’t prevent companies from offering bad tests, just doesn’t approve them).

4) A positive IgG to herpes does not tell you when you acquired the infection, just that at some point you did. Often people are exposed to the virus but don’t have their first outbreak for months or even years later. A positive herpes IgG test only tells you that at some point in time you acquired the herpes virus (1 or 2 or both depending on your results). Many people pick up herpes 1 as a child. This is innocent exposure from sharing slobbery toys in daycare or kisses from someone who is shedding the virus but has no active cold sore.

5) A positive IgG also doesn’t tell you where you have the virus. This is very important, because 50% of new genital lesions are due to herpes type. Basically, if you test positive for herpes type 1 and negative for 2 that does not mean you don’t have genital herpes. You could be carrying herpes type 1 in the mouth, the genitals, or in both places. Recurrent sores on the mouth are more likely to be type 1 and recurrent sores on the genitals are more likely to be type 2, but that’s more likely not always. If you only test positive for type 2, that could have been an oral infection.

6) How will the test change your behavior? Will it make you be more careful sexually? Well, you should be more careful anyway. Will you only date people who are negative for both herpes 1 and 2? (remember, herpes type 1 can cause genital infections). If that’s the case, will you have a sexually chaste relationship, even abstaining from kissing, for 6 months to be rested to see if you are still negative? What if you are just positive for herpes 1, because that doesn’t rule out genital herpes? If you are positive for herpes 2 and have never had a genital outbreak, it is possible that the herpes 2 you have is an oral infection and not genital.

8) The CDC does NOT recommend routine blood testing for herpes . There is no evidence that testing changes sexual behavior (see above). And the mental gymnastics about how to manage the test results are just too complex (see above).

The best reason for blood testing is when there is a specific question or diagnostic dilemma. Three scenarios might be…

1) A person has a recurrent genital ulcer that seems atypical for herpes. As part of the work up, blood tests for herpes may be ordered and, if negative, repeated in 4-6 months. This is part of a medical work up of a specific problem.

2) A person with known genital herpes who wishes to reduce the risk of transmitting the infection to their sexual partner. Taking antiviral medications can reduce this risk by about 50%. However, if the partner is positive for the same herpes virus, then the medications might not be needed. This scenario is really partner testing.

3) There is also an argument that goes back and forth about testing during pregnancy as a new infection during pregnancy close to delivery can be very dangerous to the baby. This would require weeks of posts to address appropriately, but suffice it to say that The American College of OB/GYN (ACOG) does not recommend routine blood testing for herpes during pregnancy.

Before you decide to get a blood test for herpes, get informed. Herpes blood tests are expensive and can’t tell you when you caught herpes or even if the virus in your mouth or on your genitals. What if you just want to be “Screened for everything?” Herpes blood tests are not screening tests, but tests that should be used to answer a specific problem. If your question is, “Do I have genital herpes,” that answer can’t be answered reliably with a blood test.

Remember, this post is not direct medical advice