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(MENAFN – IANS) 
London, November 16 (IANS) The accuracy of a rapid finger-prick antibody test for SARS-CoV-2, the virus responsible for Covid-19 infection, may be significantly lower than previously suggested, say the researchers.
The results, published in The BMJ journal, suggest that if 10 people of people tested had previously been infected, about one in five positive results would be wrong (false positive results).
“These conclusions contrast with a previous study (not yet peer-reviewed) that suggests the test does not give false positive results,” said the study authors from Imperial College London in the UK.
The results suggest that the test may provide a sufficient degree of accuracy for population surveillance studies, but laboratory confirmation of positive results is likely to be required if these tests are to be used to provide evidence of virus protection.
The AbC-19TM rapid test uses a drop of blood from a finger prick to see if it is likely that someone was previously infected with SARS-CoV-2.
It provides results in 20 minutes, without the need to travel to a laboratory, and is approved for use by healthcare professionals in the UK and EU.
For the results, the scientists tested blood samples in a laboratory of 2,847 key workers (health workers, firefighters and police) in England.
Of these, 268 had a previous positive PCR (positive polymerase chain reaction) result, so they were “known positive” while the remaining 2,579 had an unknown prior infection status.
Another 1,995 pre-pandemic blood samples were tested as “known negatives”.
Based on a series of analyzes, the researchers estimated that the specificity of the AbC-19 test (ability to correctly identify a true negative sample) was 97.9%, which means that 2.1% of people who do not they had a previous SARS-Cov -2 infection that was found to be erroneously positive.
They estimated the sensitivity of the AbC-19 test to be 92.5% based on PCR confirmed cases, but significantly lower (84.7%) in people with unknown prior infection status prior to the antibody test.
This difference is likely due to the test being more sensitive when antibody levels are higher, the researchers explained.
Since people with a positive PCR result tended to have more severe disease, it is likely they would have produced more antibodies.
The researchers said the lower figure of 84.7 percent is likely a more realistic estimate of the test’s sensitivity in the real world, should people choose to take the test to find out their previous infection status.
“This means that 15.3 percent of people with a previous SARS-CoV-2 infection would be lost,” the authors noted.
-IANI
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