A<unk> , often called a "NAT", (or nucleic acid amplification<unk>  - "NAAT") is a molecular technique used to detect a virus or a bacterium.  These<unk> s were developed to shorten the window period, a time between when a patient has been infected and when they show up as positive by antibody<unk> s.
The term includes any<unk>  that directly detects the genetic material of the infecting organism or virus.  There are multiple methods that fall in this group, including:
Methods based on the Polymerase chain reaction.  These<unk> s use a primer to rapidly make copies of the genetic material.
A reverse transcriptase PCR (RT-PCR) is used for HIV and other RNA viruses.
Transcription mediated amplification uses a slightly different molecular method than PCR but has the same basic principle.
Branched DNA (quantiplex bDNA)<unk> s use a molecule that links to the specific genetic material.
Ligase chain reaction
A reverse transcriptase PCR (RT-PCR) is used for HIV and other RNA viruses.
Transcription mediated amplification uses a slightly different molecular method than PCR but has the same basic principle.
Nucleic acid test
CURE
Viral load
Fluorescent treponemal antibody absorbtion 
Molecular microbiology
Syphilis/Immunoassay
Heterophile antibody test
Nucleic acid hybridization