key: cord-1025395-nmkcvyzx
authors: Poon, Kok-Siong; Wen-Sim Tee, Nancy
title: Realistic considerations for comparison between SARS-CoV-2 molecular diagnostic assays
date: 2021-03-31
journal: Biomed J
DOI: 10.1016/j.bj.2021.03.006
sha: 2d7e2ce14bc67e6daac4b33467d5c36ec9f587f2
doc_id: 1025395
cord_uid: nmkcvyzx

nan

We read with great interest the article by You et al 2020 [1] in which excellent agreement between two SARS-CoV-2 molecular diagnostic assays of different formats was reported.

The cobas 6800 SARS-CoV-2 test (Roche Molecular Systems, Rotkreuz, Switzerland) is a sample-to-result platform of high throughput. Conversely, the Taiwan CDC assay is a scalable manual test with flexibility. In the setting of a sudden and severe pandemic, the adoption of multiple diagnostic platforms for clinical testing to circumvent routine service disruption due to potential supply shortage of reagents and consumables is prudent. The Taiwan CDC assay utilises a stand-alone nucleic acid extraction process which enables polymerase chain reaction (PCR) testing of a wider spectrum of specimen types with previously published primers and probes [2] . A laboratory-developed test like this allows the detection of SARS-CoV-2 in non-respiratory swab specimens such as saliva, lower respiratory tract fluids, stool and blood while testing these specimens on the cobas 6800 SARS-CoV-2 is an off-label use of the Emergency Use Authorized test.

With 3 discordant results, the positive agreement between these two studied assays was determined to be 80% (overall N = 15). However, the positive agreement was in fact 100% when comparing the results of the E gene target detection only. The three discordant samples were very likely to carry low amount of SARS-CoV-2 since the follow-up specimens were subsequently tested positive by both assays. We would like to suggest that when there is late amplification in one of the two viral targets, either in an assay with multiple singleplex components or in a multiplex PCR assay, the PCR test should be repeated, preferably in multiple replicates. In samples with low viral load close to the assay's limit of detection 

Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR