Sunday 3 December 2023

When can I get tested to see if I have covid-19? Which one should I get?

The increase in cases, due to the omicron variant, makes many people wonder if they should seek a covid test; here we clarify the doubts

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QCOSTARICA – Given the increase in new daily cases of covid-19, due to the omicron variant, many people wonder when they should get tested and which test to get.

PCR and antigen tests are done through a nasopharyngeal swab where samples of the person’s mucus are taken. Photo: John Duran

Christian Pérez, director of the clinical laboratory of the Hospital Nacional de Niños (HNN) – National Children’s Hospital (HNN), told La Nacion that it is vital to be attentive to the possible symptoms, however mild they may be, since omicron could be confused with a cold, since its first symptoms are usually sore throat and weakness.

Therefore, if you have any of these symptoms, it is necessary that you get tested.

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  • Headache
  • Fever
  • Nasal congestion
  • Throat pain
  • Body discomfort
  • If we suspect that someone close to you is infected or positive.
  • With the omicron variant, lack of taste and smell is less common, but these are also symptoms that must be taken into account, since the delta variant still circulates in Costa Rica.
  • If we had close contact with someone positive and we do not register symptoms and we would like to find out, the ideal is to seek the test between day 5 and day 7 after we had that exposure to the virus.
  • Other less common symptoms such as diarrhea, vomiting.

Pérez stated that in the last two weeks the number of tests that have been processed has been unprecedented.

The Caja Costarricense de Seguro Social (CCSS) reports of days in which almost 10,000 samples are analyzed.

The specialist also reminds the residents that if they feel symptoms, they should not risk thinking that it is just a cold, and that they go to get tested and isolate themselves at home until the health order ends.

What test to get?

If you go to a public laboratory, one operated by the Caja or local clinic operated by a cooperative, probably, depending on the place, they will do an antigen test. This test can be taken to any area of ​​the country and its results are faster.

If the antigen test was negative, but you had contact with a positive and also have symptoms, they would do a PCR test, which is more accurate to confirm the results.

In a private laboratory, you will be able to choose between antigen test or PCR. The first is cheaper than the second. The antigen is going for between ¢20,000 and ¢40,000, while the PCR can vary between ¢45,000 and ¢80,000, depending on the laboratory. However, the differences between both types of exams go beyond the price.

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Polymerase chain reaction (PCR) tests are known as the “gold standard.” To understand why, we must first explore two key concepts when determining diagnostic test results.

Sensitivity: the probability of a test to detect infection is high. A negative result would be very close to reality and the presence of the virus could be ruled out. In other words, the higher the sensitivity, the lower the risk of false negatives.

Specificity: The chance of a test to rule out infection when you don’t have one. If the specificity is high, the possibility that a positive really is is very high. In other words, the higher the specificity, the lower the risk of false positives.

PCR tests give the most reliable results, both their sensitivity and specificity are around 95% and their chances of error are less than 5%.

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This type of test analyzes whether the person has genetic material from the SARS-CoV-2 virus. This test can determine if a person has an active infection at that moment.

The test is performed through a nasopharyngeal swab, in which a swab is inserted through the nose and mucus is extracted from the person; subsequently, a molecular biology laboratory is required to analyze the presence of genetic material of the virus. This takes more time and if the demand is high, it causes delays in delivering results.

In private labs it takes about 24 hours, at the public, it takes about five days.

The price of these tests is also higher since more reagents must be used and laboratories are required.


Antigen tests do not look for genetic material from the virus. Unlike PCR, antigen tests aim to locate SARS-CoV-2 proteins. It is also taken with a nasopharyngeal swab.

They are faster and can give the result in a matter of a couple of hours or less, because they do not require a molecular biology laboratory.

When looking for the proteins of the virus, they are most efficient between the first and fifth days that people register symptoms.

Its confidence, however, is not as high as the PCRs. Its specificity is close to 95%, but its sensitivity is around 80%, so there is a 20% risk of being positive if it is marked negative.

“You have to have a well-declared infection and you have to have a fair amount of virus in your upper respiratory tract to test positive. Negatives are not necessarily healthy; they may be, yes, or they may have such a low amount of virus that it is not detected,” explained Pérez.

The specialist indicated that these tests are not bad in themselves, but it should be taken into account that their sensitivity is lower and that is why to clear up doubts in some private laboratories they will recommend doing the PCR directly, especially if the person is a contact close to a person with covid-19 and has no symptoms or only one symptom.

Read the original in Spanish at La Nacion.

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"Rico" is the crazy mind behind the Q media websites, a series of online magazines where everything is Q! In these times of new normal, stay at home. Stay safe. Stay healthy.

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