How accurate are COVID-19 antibody tests?

How accurate are COVID-19 antibody tests?

Public Health England (PHE) have published their evaluations of the Roche and Abbott COVID-19 antibody tests, which were conducted before authorising their use across the UK.

The results show some similarities and some differences with the manufacturer’s claims about the accuracy of the tests.

The evaluations were conducted at sites in Colindale and Porton Down at the start of May, covering 1,420 samples, which is a robust study size.

The Abbott Test

PHE conclude that the Abbott test (currently offered by London City Healthcare and most medically-led providers) is a highly specific test with a sensitivity of 99.73%, which accords with the manufacturer’s reported specificity of 99.63%.

All negative samples which were tested gave a specificity of 100%, which accords with the manufacturer’s claims.

The sensitivity of the test diminishes as the time between infection and testing increases, with an overall sensitivity of 92.71%. This is lower than the manufacturer’s reported sensitivity of 97.5%.

The sensitivity of the test for samples collected more than 40 days after infection is 87.5%.

The Roche Test

When evaluating the Roche test, PHE found that the negative samples reviewed gave a specificity of 100%, which accorded with the manufacturer’s stated results.

The test gave an overall sensitivity of 83.87%, which is lower than the manufacturer’s reported sensitivity of 100%.

The sensitivity of the test increased as the time between infection and sample provision increased, to 100% when the infection was more than 40 days before the test was taken.

Conclusions and our current advice

PHE have found that both tests give results which vary from the manufacturer’s reported accuracy in different ways. Both tests are highly accurate (which is why PHE have authorised their use) and the risks of a false negative are very low.

This is a very different risk to ‘swab’ testing, when a false negative result means a patient could continue to infect others whilst unaware they had the virus. This is why London City Healthcare do not currently advocate the private provision of swab testing – multiple tests are required to have confidence in the result.

A false negative antibody test means an individual is told they do not have antibodies, when in fact they do. They cannot infect other people.

Based upon PHE’s evaluation, the Abbott test appears to be marginally better than the Roche test at accurately identifying antibodies up to 40 days after infection. The Roche test appears to be marginally better than the Abbott test at accurately identifying antibodies more than 40 days after infection.

In summary, the differences between the tests and the potential risks of a false sense of immunity if individuals receive a positive result – if they are told they have antibodies – is a potentially complicated situation.

Although we have confidence in both tests, because of the complexities, we do not believe that either test should be offered without individual clinical supervision from a named clinician.

We urge caution in purchasing any tests online, without being certain of their provenance, or without an individual clinical consultation.

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