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Polymerase chain reaction (PCR) in the diagnosis of infectious diseases
Last reviewed: 05.07.2025
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PCR is one of the DNA diagnostic methods that allows increasing the number of copies of the detected section of the genome (DNA) of bacteria or viruses by millions of times using the enzyme DNA polymerase. The tested section of nucleic acid specific to a given genome is multiplied (amplified) many times, which allows it to be identified. First, the DNA molecule of bacteria or viruses is divided into two chains by heating, then in the presence of synthesized DNA primers (the nucleotide sequence is specific to the genome being determined), they bind to complementary sections of DNA, and the second chain of nucleic acid is synthesized after each primer in the presence of thermostable DNA polymerase. Two DNA molecules are obtained. The process is repeated many times. One DNA molecule, i.e. one bacterium or virus particle, is enough for diagnostics. The introduction of an additional stage into the reaction - DNA synthesis on an RNA molecule using the enzyme reverse transcriptase - made it possible to test RNA viruses, such as the HCV virus. PCR is a three-stage process that repeats cyclically: denaturation, primer annealing, DNA synthesis (polymerization). The synthesized amount of DNA is identified by ELISA or electrophoresis.
PCR can use various biological materials - blood serum or plasma, urethral scraping, biopsy, pleural fluid, cerebrospinal fluid, etc. PCR is primarily used to diagnose infectious diseases such as viral hepatitis B, viral hepatitis C, viral hepatitis D, CMV infection, sexually transmitted infections (gonorrhea, chlamydia, mycoplasma, ureaplasma infections), tuberculosis, HIV infection, etc.
The advantage of PCR in diagnosing infectious diseases over other research methods is as follows:
- the infectious agent can be detected in any biological environment of the body, including material obtained during a biopsy;
- it is possible to diagnose infectious diseases at the earliest stages of the disease;
- it is possible to quantitatively evaluate the research results (how many viruses or bacteria are contained in the material being studied);
- high sensitivity of the method; for example, the sensitivity of PCR for the detection of hepatitis B virus DNA in blood is 0.001 pg/ml (approximately 4×10 2 copies/ml), while the sensitivity of the DNA hybridization method using branched probes is 2.1 pg/ml (approximately 7×10 5 copies/ml).
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