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PCR and ELISA - diagnosis of sexually transmitted infections (STIs) - what is the difference?

10.06.2016 By

Brochure InfectionsIn modern laboratory diagnostics for STIs, PCR and ELISA tests are widely used. Your doctor can prescribe you not only a PCR test, but also an ELISA test to detect a certain infection.

 

 

 

From the patient's point of view, such a set of tests raises a lot of questions, because all the laboratory research methods seem to be exactly the same at first glance. But despite the external similarity, there is still a difference between PCR and ELISA tests.

The ELISA test is not based on detecting the infection itself, but on detecting specific antibodies produced by white blood cells in response to foreign genetic material (viruses, bacteria, protozoa, fungi) in the body.

In contrast, the PCR assay detects currently existing infectious agents (bacteria, viruses, protozoa, fungi).

Advantages of PCR Disadvantages of PCR
  1. Direct determination of STI pathogens.
  2. High specificity of PCR diagnostics. In the process of analysis, a DNA fragment specific only to a certain bacterium or virus is isolated in the test material.
  3. High sensitivity of PCR. Detection of infection is possible even if the material taken from the patient contains only one bacterial or viral cell
  1. The possibility of a false-positive result when monitoring the efficacy of the treatment. The PCR assay can show a positive result even if the infection is already dead, "killed" by antibiotics, but its dead cells are still present in the patient's tissues. The main rule is to wait until the dead remains of the infection are completely eliminated from the body, which in the average person takes 4-8 weeks.
Advantages of ELISA Disadvantages of ELISA
  1. Identify the presence of any localized infection by blood
  2. Ability to monitor the progress of the disease over time by titer level.
  1. ELISA is indirect, that is, it does not determine the pathogen, but the immune response to it, which may have individual variations.

Only the doctor who prescribes the examination can determine the best test for diagnosis in each situation. For a comprehensive evaluation of the infection, in some cases, both the detection of the pathogen itself (PCR) and the determination of antibodies to it in the patient's body (ELISA) may be required, with follow-up after treatment.

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