Do you have herpes if your blood test comes back negative?

Answer 1

Blood tests have markedly improved the physicians' ability to properly counsel both patients and their partners. Herpes blood tests measure the body's immune response against the virus. Without infection there is no specific reaction to the virus. However, shortly after true viral infection the body responds to fight the infection. The herpes blood test measures the body's antibodies to herpes, the body's response to infection. A positive blood test indicates there are antibodies present, therefore viral infection has occurred; a negative test indicates antibodies are non­existent. All herpes antibody tests do essentially the same thing. They do not directly measure virus but the body's reaction to the virus. To look directly for virus, one must test a sore containing virus and grow the virus in the laboratory. This has the advantage of determining the virus and its type.

Blood tests will not identify a sore or its position, but an accurate blood test could be used to help diagnose herpes in people who do not get sores and in people who get them only rarely. People who might want such a test would include:

the partner who has no symptoms but who may have been the source of herpes the person with only one past episode whose culture was lost on the way to the lab the person who thinks he or she has been exposed to herpes but is not sure the couple who wants to give up safer sex precautions.

Unfortunately, the commercial tests available to your health care provider can be very confusing. Most herpes antibody (blood) tests are not truly type specific. Most antibody tests cannot accurately tell the difference between past infection with type 1 versus type 2. To further confuse things, even some widely used tests that are commonly called "type specific" are not accurately type-specific. Most commercial type specific tests are very poor at accurately differentiating antibody against herpes simplex virus type 1 from antibody against herpes simplex type 2. Many of these inaccurate tests are commercially available and they may be easily accessible to your doctor.

Inaccurate type specific or non type­specific blood tests are still useful in some settings. For example, during a first episode, an antibody test may be used, in conjunction with viral culture and typing, to determine whether that culture proven episode is a true primary or a non primary. In this case, the blood test is not used to diagnose genital herpes but whether it's a true primary; the culture and typing of a lesion specimen was used to make the diagnosis of genital herpes.

Recently, true and accurate type specific antibody tests for herpes have been developed. These tests examine directly for the body's reaction (antibody production) against a type­2­specific glycoprotein, G­d (gG­2). Very few laboratories test directly for this antibody, since commercial test kits are not routinely available for this purpose. Until new tests replace the old tests, you and your physician will have to interpret information obtained very carefully.

The Western Blot test is so specific that, as far as we can tell, there is virtually no chance for error of the type that shows a positive antibody to herpes simplex virus type 2 where none exists. On the other hand, there is always a small possibility that an antibodies to herpes simplex virus type 2 that is really present will go undetected by this method. This could happen in the case of a person who has not had time to make a good antibody response yet. In some cases, antibody may take as much as twelve or sixteen weeks to develop, especially if the primary infection was treated with an effective medication. In some rare cases, a person with culture proven, long-lasting, herpes type 2 of the recurrent variety will still have a negative Western blot after the sixteen weeks ­­­ presumably because they just do not make enough of the necessary antibody for detection. This probably occurs less than 1 percent of the time.

The Western Blot is very, very sensitive ­­­ probably 99 percent sensitive. It is also very accurate, with virtually no false positives (incorrect positive results). If a person is tested more than twelve or sixteen weeks after the possible exposure, and if the test is negative, and if the possible exposure was to type 2 herpes simplex virus, then it is very likely that bona fide infection did not take place. However, no test is absolutely without fault and this test, like all tests, should be interpreted by you and your physician, in the seeing of the clinical information, so that everyone understands all of the subtle details.

Other tests for gG­2 (type­2­specific glycoprotein), called RIA, ELISA, or EIA (other names are also possible) may also be available. These tests can determine whether there has been infection we herpes simplex virus type 2, but they do not necessarily determine whether there has been infection with type 1. EIA tests are technically much easier to perform than the Western blot, with much of the assay actually done by machine. Unfortunately, commercial kit assays for antibody to gG2 are not yet available. This situation is very likely to change ­­­ and soon. ELISA tests have been successfully used for this purpose, with one described from Atlanta, one from California, another from Sweden, and an adaptation from Australia.

Until then, if possible, be especially careful to check with your physician as to which test is being ordered and how the test will be interpreted before actually being tested. The test situation can be very confusing, because if your physician has ordered a so-called type specific EIA test that does not specifically check for antibody against gG­2 or some other type 2 specific glycoprotein, then the test answer may be of no value and should not be interpreted. So called type specific tests that often give misleading test results are most often reported as "type 2:type 1 ratios." Always check this out with your physician.

Answer 2

No