How Reliable is the Blood Test for Herpes?

Overview of herpes infections

Herpes simplex virus causes herpes simplex type 1 and type 2 infections. HSV-1 infection (herpes simplex virus type 1) is characterized by the eruption of one of more groups of vesicles on the vermilion border of the lips or at the external nares. HSV-2 infection (herpes simplex virus type 2) is characterized by eruption of similar lesions in the genitalia. Both types may reappear during other febrile illnesses. The viruses frequently become latent and may not be expressed for years.

Herpes zoster infection is caused by a herpesvirus (varicella-zoster virus) and is characterized by eruption of group of vesicles on one side of the body following the course of a nerve due to inflammation of ganglia and dorsal nerve roots resulting from activation of virus, which in most cases remains latent for years following a primary chickenpox infection. The condition is self-limited and may be accompanied by severe postherpetic pain.

Diagnosis of herpes

Herpes infections can be diagnosed using three types of tests. They are viral culture test, blood tests (serologic tests), and antigen detection tests.

Viral culture test: This can be effective to diagnose herpes if the patient has sores or any outward signs of infection. For a viral culture test, cells or fluid from a fresh sore is collected with a cotton swab and placed in a culture container and tested for the presence of herpes virus. Sometimes, more than one viral culture test may be requested by the physician to diagnose herpes infection as the lesion may have very little active virus and the test may produce a “false negative.”

Blood tests (serologic tests): Herpes blood tests measure the levels of herpes simplex antibodies in the body. Herpes simplex antibodies are produced by the body to fight off the herpes simplex virus. Blood tests detect herpes by looking for herpes antibodies in the blood. Blood tests are effective for detecting herpes infections when there are no visible sores or symptoms. If herpes antibodies are found in the blood, it means herpes simplex virus is latent in the body.

Blood tests do not require swabbing of a lesion and can performed even when there are no visible lesions or symptoms present. Type-specific blood tests are essential to detect the type of herpes infection i.e. HSV-1 or HSV-2 infection. Type-specific blood tests can accurately distinguish between HSV-1 antibodies and HSV-2 antibodies. Usually it takes 2 weeks to 3 months after exposure to herpes for antibodies to appear in the blood. Blood tests taken immediately following outbreak of herpes infection may fail to diagnose herpes as the body takes time to produce herpes antibodies.

If a person has not had any symptoms before and wants to be tested for herpes, type-specific blood test is the only way to find the status. The most reliable and widely-used type-specific blood test is the Western blot serology. These tests detect the difference between the antibodies of HSV-1 and HSV-2. A finger prick test called POCkit HSV-2 Rapid Test has also been approved for detecting herpes infection.

Antigen detection test: This is similar to culture test but used less frequently than other tests. This test does not require growing the virus in a culture container as in culture test but identifies herpes by the presence of antigens. Antigen detection assays are less sensitive than viral culture. Antigen detection mostly is done in research laboratories or large reference laboratories.

Therefore, the herpes blood tests reliable are the type-specific blood tests that can accurately diagnose herpes simplex infections. This test needs to be taken a few weeks after the exposure to herpes as the body takes some time to develop antibodies to fight the herpes virus.

References

Herpes-Coldsores.Com: Test for Herpes

National Institutes of Health Medline Plus: Serum herpes simplex antibodies