A nucleic acid test (NAT) is a technique used to detect genetic material (DNA or RNA) in samples you provide for testing. It differs from conventional tests that focus on detecting antibodies (Serological Test) or antigens for their results. NAT’s detect a particular nucleic acid sequence and thereby identify a particular species or subspecies of organism, often a virus or bacteria that acts as a pathogen in blood, tissue, urine, etc.
How Does NAAT Work?
Many NATs include a step that amplifies the genetic material—that is, makes many copies of it. This is a crucial step as genetic materials occur in very small amounts making identifying them difficult. Such NATs are called nucleic acid amplification tests (NAATs).
There are several ways of amplification or copying, including polymerase chain reaction (PCR), strand displacement assay (SDA), or transcription mediated assay (TMA).
One of the most common uses of a NAAT test is to establish the presence of Chlamydia in a patient. NAAT is used extensively for detecting STD’s. Because of the amplification process, doctors can now detect STD’s in urine samples that were previously only detectable by swab.
As NAAT’s are incredibly sensitive to even minute quantities of viral DNA, previously undetectable traces of HIV and other blood borne pathogens in blood samples can also be detected, enabling early treatment.
The simplicity of testing urine rather than relying on invasive genital or other swabs, has allowed for wide scale screening across the US to determine the prevalence of diseases such as asymptomatic STD’s in the general population. NAAT has been extensively used in the Covid-19 outbreaks to ascertain if the tested patient is infected with the SARS-nCoV2 virus.
How Reliable is NAAT?
Nucleic acid amplification tests are the most sensitive tests for the screening and diagnosis of genital chlamydial infections. NAATs are more sensitive than previously available diagnostic tests (culture, antigen detection, or nucleic acid hybridization) by at least 20 to 30%. That’s a significant difference, but according to an NIH report, not all NAAT’s are created equally and depending on the assays used, varying specificity occurs.
in other words, the different testing methods employed by the NAAT determine the outcome, but the NAAT still produces far better results than any other test we currently have access to. Confirming its results in large test groups becomes difficult when you have no other measure by which to compare the results, other testing measures being far less reliable.
If you are diagnosed as positive via a NAAT, then you’ve a very slim chance the results are not correct (a false positive) and depending on the severity of the diagnosis you can always request the test be run again using a different assay. According to the NIH report, the most reliable assay proven by their trial was the APTIMA COMBO 2 assay followed by the APTIMA CT assay. Both are manufactured by Gen-Probe, Inc.
Why NAAT is so Important
To understand this more clearly, lets use the example of a person who has contacted covid-19. Lets assume they’ve just been infected and that they are asymptomatic (not showing any symptoms). A swab is taken and sent off for testing.
A conventional Serological Test could be run on the swab, but ti will come back as negative. The reason is simple. A Serological test works by identifying antibodies in the sample. Your body produces these in reaction to the virus, but this takes time. If you’ve just been infected, your body isn’t going to be producing the antibodies yet.
The NAAT will enable technicians to find and correctly identify the Covid-19 virus itself, rather than the antibodies which you aren’t producing yet, and correctly diagnosing you as being infected. This means you can be isolated, even if you aren’t displaying any symptoms as you’re still infectious to others.
The value to both doctors and patients of being able to detect and treat diseases in their early stages cannot be over-stressed.