Double testing with lateral flow antigen test devices for COVID-19: does a second test in quick succession add value?

Abstract

Background/objectives: We investigated if performing two lateral flow device (LFD) tests, LFD2 immediately after LFD1, could improve diagnostic sensitivity or specificity for detecting severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) antigen.

Study design: Individuals aged ≥16 years attending UK community testing sites (February-May 2021) performed two successive LFD tests and provided a nose-and-throat sample for a polymerase chain reaction (PCR) test. Using the PCR result as the reference diagnosis, we assessed whether improvements could be achieved in sensitivity (by counting a positive result in either LFD as a positive overall test result) or specificity (by using LFD2 as confirmatory test).

Results: Overall, 2231 participants were included with 159 (7 %) having a positive PCR test. Of 2223 participants who completed both LFD tests, LFD results were highly concordant both with each other and with PCR tests (>97 %). The proportion of discord LFD results decreased significantly over the study period. Combined LFD usage achieved a sensitivity of 68.6 %, versus 67.1 % for either LFD individually. The specificity increased from 99.5 % to 99.8 % when using LFD2 as confirmatory test. Observed increases in sensitivity and specificity were not statistically significant. Void results were recorded for 31 (1.4 %) LFD1s, 19 (0.9 %) LFD2s and 6 (0.3 %) combined LFD tests.

Conclusions: LFD tests were highly reproducible even when they were performed by untrained users following only written instructions and without supervision. While performing two LFD tests of the same type in quick succession marginally increased sensitivity or specificity, statistically significant improvements were not detected in our study.

Keywords: COVID-19 testing; SARS-CoV-2 antigen; lateral flow device; rapid antigen test; self-test.