- Herpes: There are a number of herpes blood tests on the market, and their accuracy is somewhat variable.
Since both HSV-1 and HSV-2 can infect either the mouth or the genitals, even the best type-specific herpes blood test will not tell you where you are infected in the absence of visible sores. They can only identify whether you are infected with HSV-1 or HSV-2.
Some doctors are reluctant to test for herpes in the absence of symptoms because of the stigma associated with a positive test. However, the virus can be transmitted even when no symptoms are present.
- HIV: HIV is usually diagnosed through a blood test, although there are also oral tests that use saliva samples to test for the virus that causes AIDS.
In general, it requires both a positive initial test and a positive confirmatory test for a person to be considered HIV-positive. However, the process of confirmatory testing is usually invisible since both tests are generally done on the same blood sample.
- Syphilis: There are several different blood tests for syphilis. These can be used in combination to determine both whether you are currently infected and if you have been infected in the past.
- Hepatitis B: As with syphilis, there are multiple blood tests for Hepatitis, which can be used to determine your history of infection as well as whether you're currently infected with the virus.
If neither a urine nor a blood test is available for an STD, then it is usually identified by either visual or microscopic examination of sores or by some form of bacterial culture. These types of tests may also be used instead of, or in addition to, blood tests for the diseases listed above in certain situations.