QCOSTARICA – As of this Friday, ten private laboratories can perform the antigen test to detect the SARS-CoV-2 virus, which causes covid-19. Previously, this test could only be used at the social security level, but this year the conditions changed.
In compliance with the provisions of the General Guidelines for the use of antigen tests for the diagnosis of COVID-19, the Ministry of Health granted endorsement for the acquisition and use of antigen tests to the following laboratories:
- Hospital Clínica Bíblica
- Hospital la Católica
- Hospital Metropolitano
- Laboratorio Hospital Universal
- Laboratorio Cartín
- Laboratorio Cenahce
- Laboratorio Páez
- Laboratorio San José
- Laboratorios Echandi
- Laboratorio Labin
The approval in private health services is given with the aim of complying with the travel requirements demanded by some countries for the entry or transit of people through their territory, so to request the completion of the test it is necessary to present the air ticket of the person concerned.
Antigen tests determine the presence of viral proteins (antigens) by immunocapture (PDR-Ag) that detects the antigen by means of an antibody.
About coronavirus tests
PCR and antigen tests are the most common but they work differently.
While antigen tests look for proteins on the surface of the virus to ascertain the presence of the pathogen, PCR (polymerase chain reaction) tests are engineered to seek genetic material called RNA that instructs the virus to make these proteins.
Both tests also require a swab from the back of your nose or throat as a sample and cannot determine whether you are contagious if positive but that’s where the similarities end.
In the case of PCR, the sample is sent to a lab. This process can take hours, requires sophisticated lab equipment and technicians, and is typically done one sample at a time. Although the sample needs to be sent to a lab, the time-consuming process delivers as the results are almost 100% accurate in spotting infected people when there is virus on the swab.
In contrast, antigen tests — often referred to as rapid tests — work by mixing the sample with a solution that unleashes specific viral proteins. That combination is then applied to a paper strip that contains a bespoke antibody optimized to bind these proteins if they are present. Like a home pregnancy test, the result is reflected as a band on the paper strip.
The process doesn’t require a lab, and can be done in up to 30 minutes, but that speed comes at the cost of sensitivity. Although these tests are reliable when an individual has a high viral load, they are far more prone to false-negative results if a person has low amounts of the virus in their body.
When it comes to tests, the person who administers the test can be crucial. PCR tests are very accurate when properly performed by a health care professional, but the rapid test can miss some cases.
A positive antigen test result is considered accurate when instructions are carefully followed, but there’s an increased chance of false-negative results — meaning it’s possible to be infected with the virus but have a negative result.