How PCR Tests Work in Detecting Viruses and Bacteria

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How PCR Tests Work in Detecting Viruses and Bacteria
How PCR Tests Work in Detecting Viruses and Bacteria
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PCR (polymerase chain reaction) test is a molecular examination carried out by the method of amplification or reproduction of viral or bacterial genetic material. PCR tests are often performed to detect the presence of viruses or bacteria that cause certain diseases

One of the sampling methods for the PCR test is the swab test. An example of a disease that can be diagnosed through a PCR test with a swab test sampling method is COVID-19.

How PCR Tests Work in Detecting Viruses and Bacteria - Alodokter

In addition to the swab test, sampling for the PCR test will be adjusted according to the type of disease you want to diagnose. Several types of samples that can be used for PCR tests are samples of blood, urine, sputum, and even cerebrospinal fluid (CSF).

Purpose and Indications of PCR Test

As mentioned above, the PCR test can be used to detect the presence of genetic material present in every living thing, including viruses and bacteria. The ability of PCR tests to detect genetic material can be used to detect a number of infectious diseases, such as:

  • Gonorrhea
  • Clamydia
  • Lyme Disease
  • Pertussis (whooping cough)
  • Cytomegalovirus infection
  • Human papillomavirus (HPV) infection
  • Human immunodeficiency virus (HIV) infection
  • Hepatitis C
  • COVID-19

Preparation Before Conducting PCR Test

There is no special preparation before doing the PCR test. However, the patient will take a sample using a special method, then it will be sent to the laboratory for extraction, purification, and processing by PCR.

Patients undergoing a PCR test need to be told how long it will take for the results of this test to come out. Patients with infectious diseases that can be transmitted through droplets, such as COVID-19 or whooping cough, must comply with existing he alth protocols while waiting for PCR results.

Patients who take the PCR test by taking swab samples need to be given instructions that this procedure can cause discomfort, both during the process and after.

Sampling Procedure for PCR Test

One of the sampling methods to be further examined by PCR is through a swab test. The swab test can be done on the nose, the passage between the nose and throat (nasopharynx), or the passage between the mouth and throat (oropharynx).

The following are the steps for the swab t test that the patient will undergo:

  • The doctor will ask the patient to remove the mask and blow the nose from the nose if there is one.
  • The doctor will ask the patient to raise his head to facilitate the process of taking mucus samples.
  • The doctor will insert a swab that resembles a long cotton bud down the nose to the nasopharynx (the upper part of the throat located at the back of the nose).
  • The doctor will rotate or move the swab a few times (about 15 seconds) so that the mucus in the nasopharynx sticks to the swab.
  • After the mucus sampling process is complete, the doctor will slowly withdraw the swab device and the patient will be asked to put the mask back on.

In addition to the swab test, samples for PCR tests can also be taken from blood, urine, or cerebrospinal fluid. This will be adjusted to the type of disease that you want to detect through the PCR test.

Doctors and the medical team will provide directions and carry out sampling procedures according to the needs of the examination. If the sample required is a blood sample, blood will be drawn through a vein using a special needle.

If what is needed is a urine sample, the patient will be asked to collect urine in a special tube, to be sent to the laboratory for analysis. Specifically for cerebrospinal fluid sampling, the doctor will perform a lumbar puncture procedure.

After Sampling Procedure for PCR Test

After the sampling process is complete, samples will be sent for further processing and reading by the PCR tool. If the sample is taken using a swab test, after the mucus sampling process, the doctor will insert the swab device into a plastic tube, then close the plastic tube tightly.

This plastic tube will be put into a special tube for hazardous waste (biohazard) and taken to the laboratory for further processing and put into a PCR tool to get results. The results of the PCR test can be known within 1-2 days.

The PCR test involves 3 processes, from sampling, extraction of genetic material from the sample, amplification or duplicating of genetic material, and reading of the results. In this examination, the CT value will usually be listed.

The result of the PCR test will show positive or negative. A positive result means that the patient is confirmed to have the disease. On the other hand, a negative result means that the patient does not have the disease.

However, in some cases, the PCR test may return false positive or false negative results. A false positive means that the test result is positive, when in fact it is negative. Whereas a false negative is the opposite, showing a negative when it is actually positive.

For example, a false positive result for COVID-19 means that a person who has undergone a PCR test is considered positive for COVID-19, even though he or she is not infected with the SARS-CoV-2 virus. On the other hand, a false negative result indicates that a person who has undergone a PCR test does not have COVID-19, when in fact he or she is infected with the SARS-CoV-2 virus.

PCR Test Side Effects

The PCR test is safe for everyone and does not cause any side effects. However, during sampling, some complaints may appear, for example, discomfort in the nose when the doctor inserts the swab or bruising and pain at the injection site during blood sampling.

However, in the absence of certain medical conditions, these side effects will generally go away on their own.

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