Understanding Herpes Testing
The most important fact to know in terms of Herpes testing is that blood testing with an IgG test is the BEST test for diagnosing the disease.
When you first see the doctor for a suspicious genital ulcer, your health care provider may ask a lot of really personal and embarrassing questions. Know that having an accurate sexual history as well as a description of your symptoms is very important as your health care provider evaluates you. Be honest.
However, medical history and physical examination alone can not diagnose herpes.
I've seen a lot of genital herpes, but it's easy to be fooled. I've had patients who had lesions in unusual places or didn't have a typical story that I mistook for abscesses - only after they failed antibiotics did I do the culture and verify that it was herpes.
On the other hand, I've seen some very typical appearing ulcers on the genitals that turned out NOT to be herpes.
Studies have shown that health care providers, based on a clinical exam alone, incorrectly identify lesions that are not really herpes up to 20% of the time. So, if you have an ulcer or lesion, always insist on lab testing in addition to an exam.
There are two main types of lab testing:
- "Swab" tests that take a culture of a lesion or ulcer
- Blood tests.
Swab tests include viral cultures, Polymerase Chain Reaction (PCR) swabs, Tzanck smears and Pap smear. For a viral culture, a synthetic swab is rubbed vigorously over abnormal skin, then placed in a liquid and sent to the lab. It is then placed in a medium to see if it grows a herpes virus.
The traditional culture can take 7-14 days to grow. Further testing is then needed to see if the virus is HSV type 1 or type 2.
NOTE: a negative viral culture does NOT always mean that you don't have herpes. It simply means that there was insufficient virus to culture OR there was no virus present in the sample.
In fact, one study found that in 76% of cases, a viral culture came back NEGATIVE in a person who really DID have herpes when blood PCR (see below) testing was done.
Therefore, all negative cultures should be followed up with a blood test 3-4 months after possible exposure to see if the person really does have herpes.
The PCR swab test is obtained just like the viral culture, then using specialized laboratory techniques; the sample is amplified many times. This test is much more sensitive in picking up herpes than a viral culture. But again, disease can be missed.
Tzank smears have been around for a long time. Basically, cells are collected on a swab, smeared on a slide, stained with a special stain and then examined under a microscope. Cells infected with herpes virus have a typical appearance. When done properly, and read by an experienced lab person, it can be very specific for herpes. However a Tzanck smear does not rule out a herpes infection. It needs to be followed up in 2-4 months with a blood test to verify a true negative. Also the Tzanck smear can't differentiate between HSV1 and 2.
- "Swab" tests that take a culture of a lesion or ulcer
Most women are familiar with the Pap smear, which is used to detect cervical cancer. There is a new test, dubbed the "silver pap" that includes a herpes PCR swab test in addition to the GC (gonorrhea and Chlamydia) tests that are performed at this time. However, the test is done at the time of a Pap, and not necessarily at the time of an outbreak. Therefore, a negative test doesn't mean that you don't have herpes. You just didn't have active infection at the time of the Pap.
Blood tests look for antibodies to the herpes virus. Therefore, a positive antibody test means that a person definitely has herpes. However, it can take 3-4 months after a possible exposure to produce enough antibodies, therefore if you can identify the exposure, you should wait that long to have the test.
Some older herpes blood tests (called crude antigen tests) can detect the herpes virus, but can't differentiate between types 1 and 2. It's still done, but it's pretty worthless.
Newer tests are called type-specific serologic tests. They can distinguish between HSV 1 and 2. The best tests measure a type of antibody called IgG, which is present a few months after infection.
You can also test for IgM antibodies, but they can erroneously pick up other herpes viruses like chicken pox or mono. These tests should be avoided.
At last count, there were five of IgM antibody blood tests available:
HerpeSelect tests currently are the most accurate tests available for most physicians. They test for IgG, and are very sensitive and specific for herpes. When your physician has your blood drawn for herpes testing and sent off to a lab, chances are, this is usually what they are ordering. The two largest laboratories, Quest and LabCorp use this test, as well as most smaller community labs.
The Biokit HSV-2 (SureVue HSV-2) test is an in-office blood test. The blood is collected via finger prick - like a blood sugar test. It takes five- ten minutes to run. It's highly sensitive for diagnosing HSV2, but it can only be performed in a nationally certified lab - and most physician's offices are not. It used to be called POCkit HSV-2.
The Captia test is a newer FDA approved test, but it's not widely available.
The best test, the Western Blot, is only available at the University of Washington where it was developed. It's expensive and takes awhile to perform. It is not FDA approved. However, if your HerpeSelect test is indeterminate (not definitely positive or negative) or weakly positive, it may be worth it to you to send a blood sample to the University. They accept samples from anyplace in the U.S.
Interpreting the results of your IgG test.
HSV-2 Antibodies present - this means that you have HSV-2 infection.
HSV-2 Antibodies NOT present: With 95-98% accuracy, you do NOT have genital herpes, unless you acquired it very recently.
HSV-1 Antibodies present: this means you have HSV-1 infection. Usually the virus is normant in the nerves of the mouth and eye, though some people do have genital HSV-1 infection
Neither HSV-1 or HSV-2 Antibodies present: you are not infected with either HSV-1 or HSV-2. Note that there is a small chance that have been recently infected and have not made antibodies yet.
Timing is EVERYTHING
If you are going to go to the trouble of having herpes testing, be sure that you time the testing right. Know that it can take 3 months (or up to 6 months!) for the IgG antibody to be detected, therefore a test drawn to soon after an exposure may be falsely negative. Have it redrawn after 3-4 months to be safe.
ASK Questions and be prepared! Some people feel weird questioning their doctor about which test is being ordered. DON'T. It's your health. NEVER settle for ambiguous results and misinformation. Perservere in getting the best answers.
Published On: May 09, 2008