As we know, there are different tests that help us diagnose coronavirus infection, the cause of COVID-19, but there are doubts about the differences between them. In this article and the following ones, we explain everything you need to know about the main tests to diagnose COVID-19.

The most commonly used tests to diagnose COVID-19

Currently the most commonly used tests are:

1. PCR test (which stands for 'Polymerase Chain Reaction'): This is the main reference test and can detect whether there are fragments of the virus's genetic material in the upper respiratory tract. Depending on where the sample is analyzed, the result will be available within the next 12 to 24 hours, although it may take a few days.

   You can read more about PCR here.

2. Rapid antigen detection test: This test does not identify the genetic material of the virus, but rather detects the proteins present in the virus in the respiratory sample. The results of this test are more reliable if it is performed within the first 5 days of the onset of symptoms, since the viral load is higher during these days. Currently, it is being studied whether this test would be useful in the case of people who are asymptomatic (they do not present symptoms even though they are infected) but at the moment it is not valid. The results can be obtained after 15 minutes of performing the test.

Can we take the positive or negative result with 100% certainty?

Regardless of the test, the answer is that the results are not 100% reliable, given that there may be some margin of error depending on the viral load.

The sensitivity (a term that we will explain in the following articles) of the PCR It depends on the viral load, which means that it depends on the concentration of virus we have. If we test negative, we cannot say with 100% certainty that we are not infected, since we may be infected, but not with enough viral load to be detected by the test.

The sensitivity of the antigen test is lower than that of the test PCR, which makes it less reliable. In addition, the analysis of the sample must be done within a maximum of 2 hours from the time it is taken. If this time is extended, the sensitivity will be even lower.

Both tests will serve to determine if we have an active coronavirus infection (COVID-19). However, they use different methods, so it will be necessary to evaluate which test is applied in each case.

If you want more information about tests to diagnose COVID-19 and other topics related to the disease, we invite you to join our Community insp@ir Re-COVID  where you can share experiences and ask questions to our healthcare professionals.

Author:
Teresa García Barredo, Respiratory Physiotherapist at the Lovexair Foundation and HappyAir Coach

Reviewers:
Eva Maroto López, Respiratory Physiotherapist of the Lovexair Foundation and Coach HappyAir
Lila Martínez Ucha, Communication Department of the Lovexair Foundation

Bibliographyed

Monitoring and control strategy and indicators
How PCR and rapid coronavirus tests work and how they differ
Coronavirus test differences rapid PCR test covid19 Spain
SEIMC positioning on COVID19 microbiological diagnosis

Last updated on 7 March, 2026