Tests that significantly shorten the waiting times for the results and simplify the taking of samples compared to the PCR tests hit the market. In addition, they match their reliability by up to 97%.
A few days ago we woke up to the news that the Health Minister of the Community of Madrid, Enrique Ruiz Escudero, announced the purchase of two million rapid tests capable of detecting people infected with SARS-CoV-2. Many of us thought that it was the well-known rapid tests that look for antibodies with a drop of the patient’s blood … but it was not.
These were new rapid antigen tests, which are more reliable and convenient, and which could also have a very positive impact on the control of the pandemic. Given this, the question arises: are they really as good as they seem?
If you want to discover what they are and what they really are, I invite you to continue reading. I assure you that very soon you will sneak into all the conversations you have, as the antibody tests did in their day.
ARE THEY REALLY “NEW”?
Actually, this is not so. Throughout April the governments of many North American and European countries (including ours) acquired a batch of this type of test from a Chinese manufacturer. What happened then, we all remember: the fact that its sensitivity did not exceed 30% forced its return. And it generated discomfort and suspicion.
This time the regulatory agencies, such as the US FDA, have been serious about regulating this type of test in the market, and in the last week of last August, they authorized the marketing of two antigen tests to two pharmaceutical companies.
HOW ARE THEY DIFFERENT FROM ANTIBODY TESTS?
Antigen tests search our fluids for pieces or remains of RNA from the SARS-CoV-2 virus. On the other hand, antibody tests look for the presence of defenses that our body produces against this virus.
In other words, with these new tests, as is achieved with PCR, we would detect those people who are currently developing the disease [and could be isolated and controlled] and not those who have already had it.
SO THESE ‘NEW’ VERSIONS, ARE THEY REALLY RELIABLE?
Without reaching the reliability of a PCR test, the tests that detect the presence of antigens offer more than acceptable results and they coincide 97.6% with the PCR technique. What’s more, these tests are even exactly as reliable as a PCR if they are performed within the first three days of the onset of symptoms. Hence, its usefulness for mass use.
The antigen tests show, on average, between 87% and 97% reliability .
AS FOR THE TIME REDUCTION THEY PROMISE, HOW FAST ARE THEY?
It depends on the laboratory that makes it. But the difference between the different models does not exceed three minutes. Thus, if we look at the British test (which is the one that probably reaches our country first because it already has the CE marking), we will obtain the result in 12 minutes. For its part, the American test offers positive or negative in a quarter of an hour. This represents a great step, a complete revolution in the control of the spread of the virus if we compare it with the PCR tests, which take several hours to provide the definitive results.
HOW IS THE TEST DONE?
The process is much easier than the PCR test, being similar to the popular pregnancy test … but without urine involved. A sample of the mucosa of the patient’s nose is taken using a swab (a thin stick with a small cotton ball at the end), and the sample is then placed on a piece of cardboard the size of a credit card containing a reagent.
HOW DO THE RESULTS APPEAR?
After a few minutes (12 or 15, depending on the model used), we can read the results directly on the cardboard: one colored line if the result is negative and two lines if, on the contrary, the result is positive.
COST OF THE TEST, MORE EXPENSIVE OR CHEAPER THAN A PCR?
According to the laboratory itself, each test has a final price of $ 5 (just over four euros).
WILL THIS TEST MAKE PCR GO AWAY?
No, PCR tests will continue to be performed in some cases, but undoubtedly much less PCR will be performed.
These antigen tests can be carried out directly in primary care centers, out-of-hospital health care, nursing homes … especially sensitive places that until now depend on a nearby laboratory where samples can be sent in order to know the health status of patients and residents. This implies certain independence and a better diagnostic approach.
WHAT ADVANTAGES DOES IT HAVE?
Its speed of detection of the presence of the virus will make the treatment and control of the pathogen much easier and more effective, reducing preventive isolation times until the result is known, which, on too many occasions, extends beyond a few hours.
Their simplicity and low cost will also make them common in work and educational centers, where they will serve to rule out or confirm possible outbreaks among the center’s staff or students.