There are several different kinds of nucleic-acid amplification tests, but they are all based on the same principal. A nucleic-acid amplification test uses a series of repeated reactions to make numerous copies of the DNA or RNA that doctors are trying to detect. That amplifies the signal of the nucleic acids in the test sample so that they are easier to identify.
The process of amplifying bacterial or viral nucleic acids is not usually the actual STD test. Instead, once the amount of DNA or RNA has been increased in the sample using PCR or LCR, more conventional tests are used to detect it. These tests usually involve some form of nucleic acid hybridization, where the sample is probed with an artificially produced complementary strand of DNA or RNA that has been labeled in some way that makes it easy to detect.
Nucleic-acid amplification tests are incredibly useful for STD testing since they allow doctors to detect a STD pathogen even when only a very small number of organisms are present. It is this sort of technology that has made it possible to do urine testing for STDs that were previously only detectable by swab. Furthermore, since nucleic-acid amplification tests are incredibly sensitive to even small amounts of viral DNA, they are very important for screening the blood supply - allowing the detection of HIV and other blood-borne pathogens that might otherwise be missed.
There are also non-amplified nucleic acid tests available for certain STDs, such as gonorrhea and chlamydia. Non-amplified nucleic acid hybridization tests are more likely to be used when large amounts of bacterial or viral DNA (or RNA) would be expected to be present - such as in a urethral swab or in a bacterial culture sample. In such circumstances, no amplification is necessary, because if DNA or RNA is present, it should be present in detectable amounts.
Nucleic-acid amplification tests are incredibly sensitive methods of detecting whether a bacteria or virus is present in a biological sample. When it comes to detecting genital herpes in a sore from a person who has symptoms, these tests serve as a viable alternative to viral culture, which can be difficult for some laboratories to perform. Unlike herpes blood tests, such nucleic acid amplification testing still involves direct determination of whether a virus is present the sample rather than looking for anti-herpes antibodies.
Nucleic-acid amplification has also allowed for an expansion of chlamydia and gonorrhea screening around the country, since such screening can now be done on urine samples instead of requiring a urethral or cervico-vaginal swab. It has thus become easy to test large numbers of young men and women for STDs in a variety of both clinical and non-clinical settings, since collecting urine requires no medical expertise.
Researchers have also used nucleic-acid amplification tests to get more information about the extent of the problem of asymptomatic STDs in the U.S. Large scale NAT based screening programs have been implemented in the military, in urban teenagers, in men who have sex with men, and in other high-risk and low-risk groups.