Sexual Health Monday July 25, 2011

What is a PCR test?

We recently added two new PCR tests to our website. IN order to help you select the best test for you, we thought it would be helpful to provide information on PCR testing and how it works to help identify the presence of a specific STI.

What is a PCR test?

Developed by a scientist named Kary Mullis, PCR stands for Polymerase Chain Reaction. This type of test allows laboratories to create copies of a specific type of DNA sequence, without the need to culture bacteria in a laboratory. This means that some pathogens (germs) that can't be amplified by using regular culturing techniques in a laboratory can be isolated and identified. PCR testing also doesn't require a large sample of DNA to be able to detect bacteria or viruses, which means that it can be effective at assisting the detection of a viral or bacterial element that is sometimes very hard to trace under other circumstances (urine).

Although traditionally PCR tests were mostly used to identify STIs such as HSV-1 and HSV-2 (genital herpes) when testing spinal fluid (in cases where these viruses are thought to have started to affect the brain), home test kits are now available. These tests can help patients take a lesion swab at home to test for HSV-2 or syphilis or a vaginal swab to test for the presence of bacterial vaginosis (gardnerella vaginalis).

How do they work?

A PCR test involves three steps, which are performed in an automated cycle, which helps regulate temperature during PCR testing. Temperature is very important in PCR testing and each of the three steps, which usually take around two hours to complete in full, are conducted at a different temperature.

These three steps are: denaturation, annealing and extension. During these steps, PCR uses the same molecules that your body uses to duplicate DNA, by first splitting the dual DNA at a high temperature and then at a lower temperature allowing 'primers' to attach to these individual strings. The final step occurs at a medium temperature of 72°C and this is when polymerase enzymes are able best able to duplicate DNA. In this way scientists are able to create almost endless amounts of duplicates to perform tests on, without requiring a large amount of viral or bacterial DNA.

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