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Diagnostic accuracy of serological tests for covid-19: systematic review and meta-analysis

BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m2516 (Published 01 July 2020) Cite this as: BMJ 2020;370:m2516

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Antibody testing for coronavirus disease 2019: not ready for prime time

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Re: Diagnostic accuracy of serological tests for covid-19: systematic review and meta-analysis

Dear editor

The systematic review published in the BMJ by Bastos and colleagues [1] uses similar methods to our Cochrane review of antibody tests published the previous week [2]. Both reviews searched for studies available up to the end of April 2020 which were mainly undertaken in China in hospitalised patients. However, Bastos included fewer studies and less data (40 studies, 49 test evaluations in Bastos compared with 54 studies and 89 test evaluations in our review). Bastos et al reported the same important pattern of increasing sensitivity of the tests over time – which was the headline finding of our Cochrane review. However, the Bastos review has a headline finding related to the sensitivity of point of care tests (lateral flow assays) being much lower (66%) than the laboratory based ELISA (84%) or CLIA tests (98%) which we did not report.

This result needs to be interpreted with great caution as the studies that used point of care tests were also more likely to be those in which antibody responses were assessed in the first two weeks since onset of symptoms, when all tests are known to perform poorly. For example, they include a study from Italy where the tests were used on presentation in the Emergency Department, when sensitivity was only 18% [3]. For data on IgG, Bastos et al report that 32% of samples tested using on point of care lateral flow immunoassays were from the third week or later, compared to 69% of the samples tested using laboratory based chemiluminescent immunoassays. We found little difference between point of care and laboratory assays in our analysis as we adjusted for these differences in week of testing at the same time as comparing the test technologies. The headline finding from Bastos et al does not account for differences in week and is thus misleading - Bastos et al do report the data by week and test type in Table 6 which shows more similar results from the different test technologies for IgG in line with our findings but not data are reported for tests evaluating both IgG and IgM.

It would be unfortunate for a promising technology to be discarded based on an analytical quirk and a misleading conclusions as is evident in this report. We need to see studies which compare the accuracy of point of care tests with laboratory tests in the same patient samples before we can draw strong conclusions about the relative accuracy of these test types. It must also be remembered that point of care tests have benefits in terms of accessibility and speed over laboratory tests, which may make them preferable in some settings, even if they do not achieve exactly the same level of accuracy. Their development and evaluation is of importance and should continue.

References:

[1] Bastos ML, Tavaziva G, Abidi SK, Campbell JR, Haraoui L, Johnston JC, Lan Z, Law S, MacLean E, Trajman A, Menzies D, Benedetti A, Khan FA. Diagnostic accuracy of serological tests for covid-19: systematic review and meta-analysis. BMJ 2020;370:m2516

[2] Deeks JJ, Dinnes J, Takwoingi Y, Davenport C, Spijker R, Taylor-Phillips S, Adriano A, Beese S, Dretzke J, Ferrante di Ruffano L, Harris IM, Price MJ, Dittrich S, Emperador D, Hooft L, Leeflang MMG, Van den Bruel A. Antibody tests for identification of current and past infection with SARS‐CoV‐2. Cochrane Database of Systematic Reviews 2020, Issue 6. Art. No.: CD013652. DOI: 10.1002/14651858.CD013652. (weblink https://doi.org/10.1002/14651858.CD013652)

[3] Cassaniti I, Novazzi F, Giardina F, et al, Members of the San MatteoPav ia COVID-19 Task Force. Performance of VivaDiag COVID-19 IgM/IgG Rapid Test is inadequate for diagnosis of COVID-19 in acute patients referring to emergency room department. J Med Virol ;30:30. doi:10.1002/jmv.25800

Competing interests: No competing interests

02 July 2020
Jonathan j Deeks
Professsor of Biostatistics
University of Birmingham
Test Evaluation Research Group, Institute of Applied Health Research, University of Birmingham, Birmingham B15 2TT, UK