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.
