More Information About Herpes Tests Tests Genital herpes is a complex disease characterized by a broad range of symptoms, and the fact that the disease is occurs as outbreaks which may, or may not be apparent, followed by periods when the virus is inactive. These factors all contribute to make the diagnosis of genital herpes very difficult, even for experienced healthcare providers unless some form of test is used. Centers for Disease Control now recommend that any diagnosis of genital herpes be supported by use of appropriate test. Before we discuss the tests in the next sections, you should learn a bit about how the accuracy of any test is described. This is done using the two terms, sensitivity and specificity. These two terms are discussed in the context of genital herpes below.

Sensitivity The sensitivity of a test is the ability of that test to give a positive result with someone who actually is positive. For example, if a person has antibodies to HSV-2, the main cause of genital herpes, then a test for HSV-2 antibodies should detect this. Sensitivity is usually given as a percentage, the higher the figure the better. Sensitivity in a genital herpes test is very important; if the test indicates a negative result when, in fact, it should be positive (this is termed a "false negative"), the person being tested may not only receive inappropriate treatment, but may also not take appropriate measures to reduce their risk of passing on genital herpes. 

Specificity This is the other side of the coin to sensitivity. It is the ability of a test to give a negative result with someone who actually is negative. For example, some antibody tests which supposedly detect antibodies to HSV-2 also detect antibodies to HSV-1 (which mainly causes oral herpes). Since most adults have oral herpes, the specificity of these tests in detecting HSV-2 is very low. Specificity in a genital herpes test is important since no one wants to be told they have an incurable STD if, in fact, they don't have it. Also, if a person's healthcare provider diagnoses them on the basis of an incorrect result, then they may receive inappropriate treatment for the condition they do have.

Clinical Examination and History This is most probably the first "test" that a person's healthcare provider will do if they go to them about genital herpes. It involves collecting a history of any symptoms they may have had and, possibly, about their sexual lifestyle. Any examination may involve close inspection of the genitals and surrounding area. For women, there may also be an internal examination using a speculum. The problem with trying to make a diagnosis of genital herpes on the basis of history and examination is that genital herpes can show a very wide range of symptoms, or no symptoms at all. This means that genital herpes infections are often be confused with other diseases such a yeast or bacterial infection, thrush, or even irritations due to allergic reactions to washing powder, certain types of clothing etc., or that the symptoms go unrecognized, and hence unreported, by people with genital herpes. In a large survey (NHANES3), only 9% of those people with antibodies to HSV-2 reported having had symptoms. Other studies show report that only 17-34% of people with antibodies to HSV-2 reported having genital herpes and that 22% of people denying a history of genital herpes did, in fact, have antibodies to HSV-2. A study has shown that even for a healthcare provider who has a lot of experience at diagnosing genital herpes, a detailed history lasting over 30 minutes is no better at diagnosing genital herpes than simply asking the question "Do you have genital herpes". Studies have shown that the sensitivity and specificity of diagnosis based on history and clinical examination are generally very low - around 30%. Therefore, if the healthcare provider does not arrange or perform some sort of test, they are quite likely to misdiagnose genital herpes and this has led to calls by CDC for diagnosis of genital herpes to supported by appropriate tests, rather than be based on visual examination alone.

Tests for Virus These can take two forms. Tests for live virus, or tests for components from the virus, alive or dead.

Tests for live virus. This is termed a viral culture. It involves attempting to collect a sample of live virus from any obvious symptoms on the patient, transporting it to a laboratory, growing the virus in a test tube and then identifying its type using specialized reagents (usually fluorescent antibodies). Viral culture is currently regarded as the "gold standard" of herpes diagnosis.

Tests for viral components. These tests (often termed "antigen tests") test for the presence of certain components of the virus. These may be bits from the outer surface of the virus, or they may be virus' genetic material (DNA). These tests may use a technique called ELISA (for viral surface components) or another called PCR. PCR is a method of "amplifying" the amount of virus DNA present in a sample to make it easier to detect. Like culture, these tests involve taking a sample from any symptoms the healthcare provider finds on the patient. Viral culture and antigen tests have very high specificity. A positive result is regarded as diagnostic for genital herpes. They also have the added advantage that the virus is collected from the sores. Therefore, if the virus is identified, the healthcare provider knows that this is the virus which is causing the symptoms. Both these types of test rely on the healthcare provider being able to get a sufficient sample of the virus for the test to be able to detect it, and for viral culture the virus must remain alive for the test to detect it. Studies have shown that, for people having a genital herpes recurrence, the virus may only be alive in the blisters for 3-4 days before the body's immune system kills it. It may only be detectable by the techniques which don't require live virus for a couple of days after that. Most people have 3-4 outbreaks per year (some may have more, some may have less), so these techniques identify an infection when it is active (i.e. virus is being shed), not when it is latent. Most healthcare providers will usually only take a sample from an obvious blister or sore. So the person has to be having fairly typical symptoms before the healthcare provider can take a sample. However, typical symptoms only occur in about 20% of cases so often there is nothing which the healthcare provider can see to take a sample from. Also, some lesions may be in locations which are not visible (for example in the cervix). Taking the sample may cause some discomfort in the patient. These tests can have a low sensitivity - they may often may give a negative result with someone who has genital herpes. The virus sample may not be alive by the time it gets to the lab in which case a culture won't work, and, if the lesions are starting to heal, the immune system may have started to destroy the virus to the extent that bits of it can't be recognized in antigen tests. Also, any other infections present in the genitals can prevent the culture working - an often quoted reason for a failed virus culture is yeast overgrowth. The low sensitivity of viral culture and antigen tests means that people with genital herpes often require several culture tests before they get the correct result. One study quoted an average of 3-4 viral cultures on a person with genital herpes before the test came back positive.

Blood Tests When a person becomes infected by a foreign organism (e.g. the herpes virus) their body starts to produce a number of special molecules to fight the infection. One class of these molecules are called antibodies. Even if the infection is killed and goes away (which does not happen in the case of herpes), the body retains a "memory" of the invader. If the person is then re-infected with the foreign organism, this memory is used to quickly produce lots more antibodies and other components to quickly kill off the invader. This is the basis for immunizations (e.g. polio) - a person is given something which resembles the particular foreign organism and the body makes antibodies and the memory to it. If the actual foreign organism then invades the body after immunization, the memory generated by the immunization ensures that the immune system can quickly kill off the attacker. Antibodies to particular things can be detected a person's blood. The presence of antibodies to a particular organism means that the person has been exposed to that organism at some point in their life. Blood tests for herpes, therefore, detect antibodies to the herpes virus. The presence of antibodies is indicative of infection with herpes, but, unlike culture, will not indicate whether that infection is currently active (i.e. virus being shed) or in a latent state.

Seroconversion When a person is first infected with the herpes virus, they do not have antibodies to it. It takes the body a certain amount of time to produce antibodies to the virus and this can vary from person to person. The process where a person starts to produce antibodies to the virus is called seroconversion and usually takes about 2-12 weeks in the case of herpes infection. The length of time it takes for a person to produce detectable levels of antibody in their blood depends on 2 factors: the rate at which the person produces the new antibodies and also the amount of antibody required before the test being used to detect the antibody gives a positive result. This is called the test's seroconversion performance and this varies from test to test. Tests which have a good seroconversion performance can detect antibodies to herpes in a person sooner during the seroconversion process than tests with a poorer performance. Antibody tests may give false negative results if used on seroconverting patients.

Accuracy Blood tests for herpes may have good accuracy, around 90% or more, in most cases. This means that they are very good at giving a positive result with people who have antibodies to the herpes virus. However, blood tests can differ very widely in their ability to distinguish between HSV-1, which mainly causes oral herpes, and HSV-2 which is the main cause of genital herpes. HSV-2 and HSV-1 are very similar viruses. Therefore, a person's antibody response to one virus is similar to that caused by infection with another. In other words, if a person is infected with HSV-1, the antibodies present in their blood are very similar to those which would be there if they had an HSV-2 infection. Most adults have HSV-1. Prevalence in the USA is around 70%, although this varies from one population group to another. It is often acquired during childhood or early teens. For most people with HSV-1, their infection is an oral infection. Some blood tests cannot tell the differences between the antibodies to HSV-1 and those to HSV-2. These tests are called non-type specific serological (=blood) tests (NTSST). Some of these are marketed as "HSV-2 Tests". Since more than 70% of the adult population have oral HSV-1, they will get a positive result in these tests even though they may not have genital herpes. Therefore, the specificity of these tests for HSV-2, the main cause of genital herpes, is very low. CDC have called for the withdrawal of these tests from the market. Blood tests which are capable of telling the difference between HSV-1 and HSV-2 are available. Such tests are called type specific serological tests (TSST). One such test is called a "Western blot". This is primarily a research test and is not widely available. Type-specific serological tests first became commercially available from about mid-1999 onwards. Blood tests should be used as an aid to diagnosis.

What a blood test result means You should be aware of what a blood test result actually means, or does not mean. Blood tests should be used as an aid to the diagnosis of genital herpes; the results of such tests will be used by the healthcare provider, possibly in conjunction with a clinical history and examination, to arrive at a diagnosis. 1. A positive result in a truly type specific blood test means that the person has been infected, at some point in time, with that virus even if there currently no symptoms, or there never has been symptoms. 2. A blood test, unlike viral culture, only indicates whether a person has that infection; it does not indicate the site of that infection. While most people with HSV-1 have the infection at an oral site, it is possible to get HSV-1 at a genital site. A positive result in an HSV-1 test, therefore, confers little information about whether a person has an oral, or genital infection. However, while it is possible for a person to have an oral HSV-2 infection, this is very rare. Studies have shown that over 99% of HSV-2 infections have a genital location. Therefore, although a blood test will not say where the infection is, a positive result for a truly type-specific HSV-2 test is suggestive of a genital infection. For this reason, an article published in 1998 indicated that blood testing for HSV-1 was of little use in diagnosis of genital herpes, while blood testing for HSV-2 was useful as an aid for diagnosis in most cases of genital herpes. 3. A negative result in a HSV-2 type specific blood test does not necessarily mean that a person does not have genital herpes. The person could have genital HSV-1 (however, see above for a discussion of the limitations of blood testing for HSV-1), or the person could have a true primary infection with HSV-2 and not have yet produced detectable levels of antibody i.e. they are still in seroconversion. A person who gets a negative result from an HSV-2 test, yet suspects they have genital herpes (e.g. because they have symptoms) is usually recommended to have a second test performed some 8-12 weeks later to see if they have seroconverted. 4. A blood test will not tell a person when they were infected. Once a person has seroconverted after their primary infection, they carry antibodies to the herpes virus in their blood. There is no way of telling when a person seroconverted unless their blood was tested from a time before they were infected through to the time antibodies are found.