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Assertions of Perfection
Neither Abbott nor Roche antibody tests have “100% accuracy”.
Media organisations reported on supposed ‘100% accurate’ tests. The ITV headline was:
‘100% accurate’ antibody test could be coronavirus breakthrough
Neither Abbott nor Roche antibody tests have the claimed accuracy.
What is accuracy?
Manufacturers develop tests for the presence of antibodies. Antibodies are part of the body’s immune response to infection. In most cases, small numbers of antibodies remain in the body as memory cells.
Antibody tests (or serological tests) seek to identify those specific antibodies.
‘Accuracy’ can be a confusing term. Imagine you are testing for a virus. There are two main measures:
- Sensitivity: the proportion of infected people with a correct positive result. This is the true positive rate.
- Specificity: the proportion of healthy people with a correct negative test result. This is the true negative rate.
In formal terms: accuracy is the number of true positive plus true negative results, of all tests.
A ‘100% accurate’ test must give correct results to everyone tested. That would be a perfect test. Reality is often disappointing.
