Rapid Antigens Test: the 10 most common questions (and our answers)

27 October 2020 Leave your Thoughts

The coronavirus vaccine will take several months to arrive. The most optimistic point to the end of the year, the most pessimistic do not see it before the autumn of 2021 and the consensus seems to be around the summer of next year, as the most likely date.

The second wave seems more contagious and less lethal, but no less dangerous for that. The best way to protect and take care of our loved ones and the most vulnerable is by doing the same: much, much caution, more patience, hygiene and at the slightest sign, get tested for COVID immediately.

Without a doubt, the commercialization of rapid antigens tests is very good news to help stop this second wave and, unfortunately, a third or successive ones that are coming. As we have done with the rest of the tests, at Life Length laboratories we respond to 10 of the most common doubts that arise among our clients in reference to rapid antigen tests.

1. Are antigens tests really reliable?

Without reaching the reliability of the best test to detect COVID so far with 99.9% reliability, the PCR test, our tests that detect the presence of antigens offer more than acceptable results. With 92.9% sensitivity and 99.6% specificity, our tests are almost as reliable as PCR, if performed within the first few days of the onset of symptoms.

2. What is the difference between a rapid antigens test and a rapid antibody test?

The antigens test is capable of detecting the presence of the virus, the antibody tests are not. The rapid antibody test and the ELISA test do not detect the virus but the immune reaction generated by our body against it, that is, they detect the antibodies produced against the virus by the person’s immune system. They are indirect proof that the disease is active or has been passed.

3. What are its advantages over the PCR test?

Speed: although we are currently the only laboratory that delivers the results of the PCR tests on the same day they are performed, undoubtedly the time to know the result of these tests is its greatest advantage. The results of the antigen tests are known within 15 minutes.

Simplicity: antigens tests do not require expensive reagents, robots, or qualified technical personnel for their results and although they can be performed in the same place of patient care, the World Health Organization does not recommend that they be done in places where they are not comply with the necessary biosecurity measures, both for the safety of whoever performs the test and for the risk of contamination of the sample.

Price: they are notably cheaper than the PCR test, 125 euros compared to 60 euros for the antigens test. Therefore, it appears that they could be done more frequently than PCR, and on a larger scale.

4. Why has it taken so long to be offered in Spain?

The first antigens tests for COVID-19 bought by some American and European countries, including Spain, had a sensitivity of less than 30%, something completely unacceptable. The European and United States public health regulatory agencies got serious about regulating its distribution and only now can we have very reliable antigens tests, with sensitivities and specificities greater than 90%. Although not all that glitters is gold nor are all tests equally reliable, at Life Length laboratories we have evaluated 13 different manufacturers before choosing the test we offer.

5. What is the sensitivity and specificity of your antigens test?

The sensitivity of our antigens tests is 92.9% and the specificity is 99.6%. The confidence intervals are: Sensitivity 76.5% – 99.1%; Specificity 97.6% – 100%. Test results are usually lower in asymptomatic people and, therefore, if in doubt, a PCR test should be performed.

Sensitivity is the ability of the antigens test to detect the disease and is calculated as the percentage of true positives over the total number of patients. For example, a sensitivity of 97% means that only 3 out of 100 samples have been diagnosed as negative (healthy people) when, in fact, they were from infected individuals (positive). This 3% indicates the percentage of the so-called “false negatives”.

Specificity is the ability of the antigens test to detect healthy individuals and is calculated as the percentage of true negatives over the total number of healthy individuals. For example, a sensitivity of 98% means that only 2 out of 100 samples have been diagnosed as positive (infected) when, in fact, they were from healthy people (negative). This 2% indicates the percentage of the so-called “false positives”.

6. How is the test done and when should it be done?

To carry out this immunochromatographic test, it is necessary to collect a nasopharyngeal sample, that is, from the nasal portion of the pharynx, with a sterile rayon swab, which will later be analyzed with the rapid detection kits for SARS-CoV-2.

The Rapid Antigens Test is indicated for people with symptoms in the first days of COVID-19 evolution, and for those asymptomatic who have had recent direct contact with a person who has tested positive.

7. What are antigens?

Definition of antigen: “substance that triggers the formation of antibodies and can cause an immune response”.

It is also defined as “antigen” any molecule that penetrates our body and that the defense mechanisms identify as foreign or unknown. Therefore, in this definition the types of antigens include any element that is part of a pathogen (a virus, a bacterium, a fungus), or any toxin, allergen, etc.

These molecular structures found on the surface of viruses are recognized by the immune system that triggers the production of antibodies. Antigens testing therefore detects these structures that are part of the outer envelope of the virus, that is, the virus proteins. However, when we perform a PCR test we are detecting the presence of the genetic material of the SARS-CoV-2 virus, RNA in this case.

8. Is the negative result valid for air travel?

The rapid antigens test is not valid for traveling to other countries, at the moment. The governments of many countries require a negative PCR. At Life Length we automatically deliver the results report in English and Spanish, including the extraction date as required by some countries to cross their borders. Check here an example of the PCR test report.

9. Should I combine it with any other tests for COVID-19?

When a person decides to undergo tests, especially if they are asymptomatic, it is advisable to do both types of tests, the antigens test (or the PCR test) together with another serology test that detects antibodies, either the ELISA test or the rapid test of antibodies. The combination will tell us what phase of the disease we are in. In the first days after infection, the antigens test will be positive and the serology could be negative; later it will be the other way around: the serologies will be positive and the antigens test or the PCR test will be negative.

On the other hand, if the antigens test is negative but the person has clear symptoms of COVID-19, it should be contrasted with a PCR test immediately.

10. How much does it cost and where can I get the Rapid Antigens Test in Madrid?

The price of the antigens test for individuals is 60 euros per person. The price of the PCR test is 125 euros, the rapid antibody test costs 40 euros and the ELISA test, 60 euros. The combination of two tests carries a discount of 10 euros.

You and your family can take the tests in Madrid from Monday to Friday from 8:00 a.m. to 5:30 p.m., at our office on Calle Miguel Ángel 11, on the second floor, and you must book an appointment in advance.

Photographs: José Aragones, pixpoetry, United Nations

BOOK YOUR ANTIGENS TEST NOW OR CALL US AT 91 737 1298.

Telephone service hours: Monday to Friday from 9 a.m. to 6 p.m. and Saturdays and Sundays from 10 a.m. to 14 p.m.

Since the start of the COVID-19 pandemic, our laboratory has provided its comprehensive clinical analysis and testing services to help tackle the health crisis in Spain. We are working for hospitals, residences and corporate entities and we have contributed to the correct diagnosis of thousands of people and patients.

In our laboratory we carry out PCR tests to detect positive cases with a reliability of 99.9%, together with the rapid antigens tests and the most complete serology tests, the ELISA tests. We also offer the best quick test for the detection of IgM and IgG antibodies against the SARS-CoV-2 virus, with a sensitivity and specificity of 98.6% and 99.6% respectively.

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