Herpes Diagnosis and Testing
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If you have noticed symptoms that could be caused by the herpes virus you should visit your Doctor as soon as possible, while symptoms are still present.
Your Doctor will examine your condition and should take a swab and sample of the infected tissue or a blood test. This can be analyzed for herpes.
There are several tests that are used to diagnose herpes, some are more accurate than others. The most common methods of testing for herpes include diagnosis by:
Some clinics will use diagnostic tools other than the recommended tests. Among these, two are generally not recommended; the Tzanck test and the Pap smear, neither of which is a specific test for herpes.
Tip: If you have active symptoms and the sores have not yet healed you should ask your Doctor for a specific virus culture or assay for the herpes virus. Blood tests are generally used in cases where no visible symptoms are present.
In order to confirm a diagnosis of a Herpes infection it is necessary to prove the presence of the herpes simplex virus.
This is because it is possible for a person with genital herpes to have another sexually transmitted infection at the same time, a full genital check should be made. For women this may include a cervical smear test.
Getting herpes diagnosis and testing – What you should know:
How to know which test to get:
- Viral Culture
- Serologic tests (Blood tests)
- Antigen tests
- Comparison table for the different types of herpes tests
Important points to consider:
- What is the difference between a ‘Type-Specific’ test and one that is not?
- What can I do to make sure I am getting a Type-Specific Test?
- Why isn’t everybody tested if herpes is so widespread?
The initial examination may involve:
- sexual history
- a thorough examination
- visual examination of the genital area
For men, the examination usually includes a close look at:
- the penis
- blisters or skin lesions characteristic of herpes
- discharge from the urethra
The doctor might also swab the urethra and anus for a laboratory test.
For women, the examination usually includes:
- a pelvic examination with speculum to inspect the cervix and vagina
- inspecting the labia and the area between the vulva and anus for signs of infection
Swabs of the cervix and anus are sometimes taken for laboratory samples.
For both men and women, the lymph nodes should be checked, because swollen lymph glands often accompany herpes blisters or skin irregularities.
There are three common types of laboratory tests for genital herpes and several others that are less widely used.
Laboratory tests are usually based on two categories: sensitivity and specificity.
Sensitivity refers to the likelihood the test is correctly diagnosing herpes. Specificity is the probability of correctly saying a patient does not have herpes. Speed and cost are also taken into account.
For patients who have sores or other outward signs of infection, the leading methods are:
Viral culture looks for the presence of the virus in the lesion. Viral culture is very specific:
- it does not frequently give a positive result when something else is the culprit
- it can also be very sensitive if the specimen is adequate
- it also provides a way to tell whether the infection is caused by HSV-1 or HSV-2
A poor sample may cause sensitivity to drop. Even if herpes lesions are present, there may be very little active virus left in the lesions. In this case, the culture will come back as a “false negative” (the test says there is no herpes even when the patient has genital herpes).
Often about 20% of culture tests produce a “false negative” when a patient has a first episode of herpes. With recurrent episodes, when less virus is present, the rate of false negatives goes up to 50%.
It takes anywhere from two to seven days to get viral culture results back from the laboratory, which may mean several visits to your Doctor before a diagnosis is confirmed.
Lots of people need to be tested more than once. The viral culture often misses herpes even when it is present. Often a patient who has received a negative culture result will be asked to come back again when a new genital lesion appears so the culture can be tried a second or third time.
Serologic tests take a very different approach. They detect “antibodies. ” These are substances produced by the immune system to fight off infection.
Blood Tests (serologic tests)
Detect herpes by looking for antibodies in the blood or serum. Blood tests can be performed even when no symptoms are present. If antibodies are found in the blood, herpes simplex is latent in the body. Blood tests do not require swabbing a lesion, so they can be done long after symptoms have faded.
Serologic testing has the advantage that it can be done even when a person has no symptoms, so it is a very effective way to detect an established herpes infection.
Type-specific blood tests are ideal for those who have had a history of genital symptoms but have never had a successful confirmatory test. The sensitivity and specificity of blood tests is better than culture or antigen tests, but there are two important factors to consider.
The first factor is timing. If this is the first exposure to herpes, a person may take several weeks to develop the antibodies that the test looks for.
The second is that some blood tests cannot tell the difference between the two types of herpes, HSV-1 and HSV-2. For this reason, anyone seeking an accurate diagnosis of genital herpes must be sure to get a “type-specific” serologic test, which can accurately distinguish HSV-2 from HSV-1 antibodies. Most commercially available kit assays currently cannot make this distinction despite their claims.
Type-specificity in a blood test does not depend on the antibody class being detected (either IgM or IgG), but on what the antibodies are directed against (referred to as their antigens).
In herpes, most type specific antibodies are directed against a protein called glycoprotein G (gG). The gG in HSV-1 (called, unimaginatively, gG1) differs substantially from the corresponding gG in HVS-2 (called gG2). Therefore, herpes blood tests which are based around specific detection of antibodies to either gG1 or to gG2 will be type-specific. People who are getting a type-specific test for genital herpes should ensure that the test they receive detects antibodies to gG2 since there are still blood tests out there which claim to be type-specific but which are not.
While a blood test may reveal infection with HSV at a time when no genital symptoms are present, confirmation of the genital HSV infection is still essential. If the blood test is specific for detection of antibodies to HSV type 2, the likelihood of genital HSV infection is increased, but still not proven. The doctor may ask you to re-visit for a swab test when genital symptoms or discomfort appear.
Caution: Usually, it takes two weeks to three months after exposure to herpes for antibodies to appear in the blood. Some blood tests detect antibodies sooner than others. However, once antibodies are found they remain in the body for life.
If you have never had symptoms before but want to be tested for herpes, a type-specific blood test is the only way to find out your status. Getting tested may be relevant if you:
- are in a relationship where your partner has herpes but you have no symptoms and have never been tested
- have had an infected partner and feel you should be tested
- have had several sexual partners and want to be tested for the most prevalent STDs
The technology behind the type-specific test is relatively new. The “gold standard” of type-specific blood tests is known as the Western blot.
A number of similar tests are produced for research purposes. Commercial products are just becoming available this year. These tests detect antibodies (known as “IgG”) that differ between HSV-1 and HSV-2. It is now recommended that clinicians avoid serum tests other than type-specific tests.
There are several research labs that can perform type-specific tests, but the most reliable and widely used of these research tests is the Western blot.
The third type of test, the antigen test, is used less frequently and looks for the presence of virus in the lesion. Unlike the culture method, this test does not require growing the virus but rather seeks to identify herpes by the presence of antigens, fragments of the virus that are known to stimulate the immune response.
A swab is taken similar to the method used for viral culture. In general, antigen detection assays are less sensitive than viral culture. Antigen-detection is usually done only in research laboratories or large reference laboratories.
Antigen tests can produce results more quickly than cultures and are sometimes less expensive. However, better samples are needed than for cultures and many do not determine whether the sample is infected with HSV-1 or HSV-2.
The three different methods of herpes diagnosis:
|TEST TYPE||SPECIMEN SOURCE||ADVANTAGES||DISADVANTAGES|
|Tissue Culture||Swab/scrape lesion||Highly specific;
|Sensitivity is a
function of specimen quality and sample timing.
|Serologic Test||Finger stick/ Draw
|Test can be
performed in absence of lesions; Type-specific tests are highly
|Earliest time is 12
days post infection; some tests may not detect antibodies until 3 months
post-infection. Tests that are not type-specific have inadequate
|Antigen Detection||Swab/scrape lesion||Results more rapid
General population screening for herpes is not usually recommended. Guidelines for antibody testing are still being developed. The following situations may need serologic tests (blood tests):
- to confirm infection in a person who has had symptoms but never had a positive confirmatory test result
- to determine risk of transmitting herpes to a sexual partner
- to detect herpes as part of a routine check for STDs
- to help determine a pregnant woman’s risk of passing herpes to a newborn