Nucleic acid test
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A nucleic acid test (NAT) or nucleic acid amplification test (NAAT) is a molecular technique used to detect a particular pathogen (virus or bacterium) in a specimen of blood or other tissue or body fluid. It does so by detecting and amplifying the RNA or DNA of the pathogen, that is, making extra copies of its nucleic acids. This type of medical test was developed to shorten the window period, a time between when a patient has been infected and when they show up as positive by antibody tests such as ELISA. Whereas antibody positivity cannot occur until the immune system has had days or weeks to develop a sizable subpopulation of antibodies specific to the pathogen, a NAT can detect a pathogen as soon as it is present.
The term includes any test that directly detects the genetic material of the infecting organism or virus, such as polymerase chain reaction, ligase chain reaction, and others. Their mode of use is usually that a suspected diagnosis is narrowed down on the basis of the history and physical examination, plus or minus other lab tests relevant to the situation, and then a NAT is used to confirm or disprove the diagnosis. Most often it is confirmed, as by that point the process of narrowing down has been fairly accurate.
In 1999, new screening methods involving nucleic acid amplification and that protocol approved by FDA.
- Detects low levels of viral RNA or DNA.
- Provides additional layer of safety to the blood supply because it allows the detection of infectious agents during their incubation period.
- Have the ability to detect viral mutants and occult infections.
- Highly sensitive and specific for viral nucleic acid.
There are multiple methods that fall in this group, including:
- Methods based on the polymerase chain reaction (PCR). These tests use a primer to rapidly make copies of the genetic material.
- Branched DNA (quantiplex bDNA) tests use a molecule that links to the specific genetic material.
- Ligase chain reaction
- Transcription mediated amplification (TMA). It uses a slightly different molecular method than PCR but has the same basic principle.
- Nucleic acid sequence-based amplification (NASBA)
- Loop mediated isothermal amplification (LAMP)
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