The value of repeat patient testing for SARS-CoV-2: real-world experience during the first wave

Abstract

Introduction: Reports of false-negative quantitative reverse transcription PCR (RT-qPCR) results from patients with high clinical suspension for coronavirus disease 2019 (COVID-19), suggested that a negative result produced by a nucleic acid amplification assays (NAAs) did not always exclude the possibility of COVID-19 infection. Repeat testing has been used by clinicians as a strategy in an to attempt to improve laboratory diagnosis of COVID-19 and overcome false-negative results in particular.

Aim: To investigate whether repeat testing is helpful for overcoming false-negative results.

Methods: We retrospectively reviewed our experience with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing, focusing on the yield of repeat patient testing for improving SARS-CoV-2 detection by NAA.

Results: We found that the yield from using repeat testing to identify false-negative patients was low. When the first test produced a negative result, only 6 % of patients tested positive by the second test. The yield decreased to 1.7 and then 0 % after the third and fourth tests, respectively. When comparing the results produced by three assays, the Centers for Disease Control and Prevention (CDC) SARS CoV-2 RT-qPCR panel, Xpert Xpress CoV-2 and ID NOW COVID-19, the ID NOW assay was associated with the highest number of patients who tested negative initially but positive on repeat testing. The CDC SARS CoV-2 RT-qPCR panel produced the highest number of indeterminate results. Repeat testing resolved more than 90 % of indeterminate/invalid results.

Conclusions: The yield from using repeat testing to identify false-negative patients was low. Repeat testing was best used for resolving indeterminate/invalid results.

Keywords: COVID-19 laboratory diagnosis; SARS-CoV-2; repeat testing.