ABC Medical Center > PCR Test

What is PCR Test?

21:59 - 4 May , 2021

Medical procedure



Polymerase chain reaction or PCR tests are a set of prompt and reliable diagnostic tests that are used to detect genetic alterations, infectious diseases, and cancer cells that cannot be detected with other types of tests.

Through copies, PCRs identify the DNA and RNA of the virus or infectious agent, as well as the cellular abnormality in the analyzed sample.

They have become very important during the COVID-19 pandemic since it is a fast and accurate way to know if you are infected.

One of the great advantages of PCR is that they can find pathologies in their early stage, which allows timely treatment; unlike other types of tests that cannot identify diseases until they are already in more advanced stages and there are enough antibodies to be detected.

The procedure for performing a PCR test is as follows:

  • A sample of some body tissue or fluid such as blood, saliva, or mucus is taken.
  • When placed in specialized equipment, an enzyme called polymerase is added to the sample to make copies.
  • In a short time, millions of copies are produced in which if there are any pathogens or cancer cells they are detected by the equipment.

In the case of COVID-19 and some other viruses, since they only have RNA, conversion to DNA is required so that they can be copied. In this case, a reverse transcription PCR test is used.

How samples are obtained:

There are several ways to take samples to perform PCR tests, but the most used are:

  • Blood draw: the sample is taken through a syringe inserted into a vein in the arm.
  • Nasal swab: there are three types of swabs depending on where you want to take the samples (nostril, middle nasal concha, and nasopharyngeal).

Nostril swab:

  • A swab is inserted and rotated in the nostril for 12 seconds.
  • The swab is removed and the procedure is repeated in the other nostril.

Middle nasal concha swab:

  • A swab is inserted deep into the nostril and rotated for 12 seconds.
  • The swab is removed and the procedure is repeated in the other nostril.

Nasopharyngeal swab:

  • A swab is inserted into the nostril until it reaches the top of the throat.
  • It is rotated for 12 seconds.

Potential risks:

There are practically no risks in PCR tests since blood extraction can only cause slight bleeding or form a temporary bruise.

In the case of a nasal swab, it can cause discomfort such as cough, nausea, or sore throat, symptoms that disappear immediately at the end of the sampling.

PCR tests have become a highly effective tool to control the spread of diseases because they allow timely and early diagnoses that help treat diseases when they have not yet developed, which favors the patients’ recovery.

Our Clinical Laboratory offers a service integrated by a multidisciplinary group of health professionals that support clinical diagnosis, whose purpose is to provide the tools that allow the doctor to integrate the information to study, prevent, diagnose, and provide the best treatment.

Related centers and departments:


  • Álvarez-Ojeda MG, Saldaña-Fuentes C, Ballesteros-Elizondo MR, et al. Comparación de las pruebas: reacción en cadena de la polimerasa (PCR), serología y hemocultivo con respecto a sensibilidad y especificidad, para la detección de Brucella spp en muestras humanas. Gac Med Mex. 2015;151(5):620-627.
  • Cárdenas-Bravo L, Cabrera-Rayo A, Pérez-Barragán E, et al. Recursos diagnósticos en la infección por SARSCoV- 2. Med Int Mex. 2020;36(Suppl: 2):26-28.
  • Morales-Cadena GM, Fonseca-Chávez MG, Valente-Acosta B, et al. Comparación del rendimiento diagnóstico clínico versus la prueba rápida durante dos temporadas de influenza. Rev Sanid Milit Mex. 2018;72(5-6):289-294.
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    The dissemination of the content of this material is for informational purposes only and does not replace, under any circumstance or condition, a consultation with a specialist doctor, for which the ABC Medical Center is not responsible for the different use that may be given to it. If you require more information related to the subject, we suggest you contact the specialist doctor you trust directly.