{"id":47800,"date":"2020-06-16T18:56:41","date_gmt":"2020-06-16T17:56:41","guid":{"rendered":"https:\/\/blogs.bmj.com\/bmj\/?p=47800"},"modified":"2020-06-16T19:00:45","modified_gmt":"2020-06-16T18:00:45","slug":"judging-the-value-of-serology-tests-for-covid-19-caution-is-required-in-interpreting-results","status":"publish","type":"post","link":"https:\/\/blogs.bmj.com\/bmj\/2020\/06\/16\/judging-the-value-of-serology-tests-for-covid-19-caution-is-required-in-interpreting-results\/","title":{"rendered":"Judging the value of serology tests for covid-19\u2014caution is required in interpreting results"},"content":{"rendered":"

Testing for covid-19 is critically important for the management of disease and prevention of spread. There has been understandable concern about the need to develop good tests and ensure that the tests which are used perform well. The debate has been particularly heated for serology tests (tests for antibodies to the SARS-CoV-2 virus) which are being rolled out as part of the UK government’s testing and contact tracing strategy, but with concerns remaining about the tests and how effective the strategy will be. [1]<\/span><\/p>\n

But what evidence has been used to inform decisions on which serology tests to use and whether the tests chosen are fit-for-purpose? In my view, much greater care is required in understanding and using the results of the available research.<\/span><\/p>\n

Official comments on the best serology tests have predominantly relied on the concept of test accuracy, frequently expressed as estimates of sensitivity and specificity.<\/span><\/p>\n

Concerning antibody tests which had been ordered by the UK in early April, John Newton, national coordinator of the UK Coronavirus Testing Programme, said \u201cAll the tests that have been made available have been tested. None of them performed well enough. In particular they didn\u2019t have sufficient sensitivity, which is the ability to correctly identify people who have been infected. We set a clear target for a test to achieve and none of them frankly were close.\u201d [2]<\/span><\/p>\n

And concerning the announcement of validated antibody tests in May, Newton said an independent evaluation carried out at the PHE Porton Down centre reported that the test was a \u201chighly specific assay with specificity of 100%.\u201d [<\/span>1]<\/span>\u00a0\u00a0<\/span><\/p>\n

Test accuracy seeks to measure the ability of a test to identify a target condition by comparing the results obtained by that test relative to another test which \u201ctruthfully\u201d captures the target condition, the so called \u201creference standard.\u201d Tests which correctly identify a high proportion of samples who have the target condition by the reference standard have high sensitivity; tests which correctly identify a high proportion of samples who do not have the target condition by the reference standard have high specificity. The concept is absolutely dependent on having a reference standard which captures the target condition.\u00a0<\/span><\/p>\n

But what is the \u201ctarget condition\u201d for serology? Although not as straight-forward as if we were considering the diagnosis of a clearly characterised disease like lung cancer, there are several options:<\/span><\/p>\n