While the rush for laboratories is taking place ahead of the holidays, the reliability of certain Covid-19 antigenic tests is questionable. For example, the National Medicines Agency asked pharmacists on Tuesday to no longer use the VivaDiag rapid tests because of too many false positives.
“The investigations carried out by the ANSM confirm that the performance and safety of users of this device are not guaranteed. We, therefore, ask all dispensing pharmacies to no longer use the VivaDiag Rapid Test SARS- CoV-2 Ag and quarantine all batches in your possession, “said the ANM in a statement.
All rapid tests – antigens – are not created equal. An AP-HP team carried out a study on this subject. Published in early December, and conducted by Professor Jean-Michel Pawlotsky, Henri-Mondor hospitals in Créteil, it covers nine tests, after the first series of six other tests in October. Sensitivity (ability to detect positive cases) and specificity (for negative cases) serve as indicators.
Result: “Among the nine tested, the AMP, Novel, and Sofia tests demonstrated the best performance (…) in terms of sensitivity and specificity.” The first study in October highlighted the Abbott, Biosynex, and AAZ tests, considered to be the best performing. Conversely, “on the basis of the data studied, the CerTest, GenBody, Nadal, GenSure, Quick Profile and Toda tests have not demonstrated sufficient sensitivity to be used in the indications for rapid antigenic tests”, continues the AP-HP. All however showed a specificity of 99% at the lowest.
PCR remains the benchmark
However, the most reliable antigenic tests do not certify 100% that the patient is indeed negative. The AP-HP also recommends them rather for mass screening. “We detect people with a very high viral load, the most contagious, (but) we miss a lot those whose viral load is low,” explained Jean-Michel Pawlotsky in October. With L’Express, the professor at the Créteil hospital specified last week that “in some cases, nearly 40% of positive samples have not been identified. These are therefore as many patients who would have had a negative test. , who would have been wrongly reassured and could have continued to contaminate those around them “.
Getting tested remains a useful gesture “if thanks to this, non-symptomatic positive people identify and isolate themselves”, epidemiologist Antoine Flahaut told AFP. But it would be “dangerous to consider that it is a certificate of non-contagion. One can be tested negative and carrier of the virus”, in particular with these rapid antigenic tests, less reliable.
Although the time to get the result is longer, PCR tests are still the gold standard. In addition, “the maintenance of barrier gestures and distance remains essential, even with a negative test”, underlines for its part the DGS.
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