tetano
Editor, Senior Moderator
Clin Infect Dis
. 2021 Feb 3;ciaa1382.
doi: 10.1093/cid/ciaa1382. Online ahead of print.
The Limit of Detection Matters: The Case for Benchmarking Severe Acute Respiratory Syndrome Coronavirus 2 Testing
Ramy Arnaout[SUP] 1 2 3 [/SUP], Rose A Lee[SUP] 1 2 4 [/SUP], Ghee Rye Lee[SUP] 5 [/SUP], Cody Callahan[SUP] 6 [/SUP], Annie Cheng[SUP] 1 [/SUP], Christina F Yen[SUP] 2 4 [/SUP], Kenneth P Smith[SUP] 1 2 [/SUP], Rohit Arora[SUP] 1 2 [/SUP], James E Kirby[SUP] 1 2 [/SUP]
Affiliations
Abstract
Background: Resolving the coronavirus disease 2019 (COVID-19) pandemic requires diagnostic testing to determine which individuals are infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The current gold standard is to perform reverse-transcription polymerase chain reaction (PCR) on nasopharyngeal samples. Best-in-class assays demonstrate a limit of detection (LoD) of approximately 100 copies of viral RNA per milliliter of transport media. However, LoDs of currently approved assays vary over 10,000-fold. Assays with higher LoDs will miss infected patients. However, the relative clinical sensitivity of these assays remains unknown.
Methods: Here we model the clinical sensitivities of assays based on their LoD. Cycle threshold (Ct) values were obtained from 4700 first-time positive patients using the Abbott RealTime SARS-CoV-2 Emergency Use Authorization test. We derived viral loads from Ct based on PCR principles and empiric analysis. A sliding scale relationship for predicting clinical sensitivity was developed from analysis of viral load distribution relative to assay LoD.
Results: Ct values were reliably repeatable over short time testing windows, providing support for use as a tool to estimate viral load. Viral load was found to be relatively evenly distributed across log10 bins of incremental viral load. Based on these data, each 10-fold increase in LoD is expected to lower assay sensitivity by approximately 13%.
Conclusions: The assay LoD meaningfully impacts clinical performance of SARS-CoV-2 tests. The highest LoDs on the market will miss a majority of infected patients. Assays should therefore be benchmarked against a universal standard to allow cross-comparison of SARS-CoV-2 detection methods.
Keywords: SARS-CoV-2; antigen detection; cycle threshold; limit of detection; viral load.
. 2021 Feb 3;ciaa1382.
doi: 10.1093/cid/ciaa1382. Online ahead of print.
The Limit of Detection Matters: The Case for Benchmarking Severe Acute Respiratory Syndrome Coronavirus 2 Testing
Ramy Arnaout[SUP] 1 2 3 [/SUP], Rose A Lee[SUP] 1 2 4 [/SUP], Ghee Rye Lee[SUP] 5 [/SUP], Cody Callahan[SUP] 6 [/SUP], Annie Cheng[SUP] 1 [/SUP], Christina F Yen[SUP] 2 4 [/SUP], Kenneth P Smith[SUP] 1 2 [/SUP], Rohit Arora[SUP] 1 2 [/SUP], James E Kirby[SUP] 1 2 [/SUP]
Affiliations
- PMID: 33532847
- DOI: 10.1093/cid/ciaa1382
Abstract
Background: Resolving the coronavirus disease 2019 (COVID-19) pandemic requires diagnostic testing to determine which individuals are infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The current gold standard is to perform reverse-transcription polymerase chain reaction (PCR) on nasopharyngeal samples. Best-in-class assays demonstrate a limit of detection (LoD) of approximately 100 copies of viral RNA per milliliter of transport media. However, LoDs of currently approved assays vary over 10,000-fold. Assays with higher LoDs will miss infected patients. However, the relative clinical sensitivity of these assays remains unknown.
Methods: Here we model the clinical sensitivities of assays based on their LoD. Cycle threshold (Ct) values were obtained from 4700 first-time positive patients using the Abbott RealTime SARS-CoV-2 Emergency Use Authorization test. We derived viral loads from Ct based on PCR principles and empiric analysis. A sliding scale relationship for predicting clinical sensitivity was developed from analysis of viral load distribution relative to assay LoD.
Results: Ct values were reliably repeatable over short time testing windows, providing support for use as a tool to estimate viral load. Viral load was found to be relatively evenly distributed across log10 bins of incremental viral load. Based on these data, each 10-fold increase in LoD is expected to lower assay sensitivity by approximately 13%.
Conclusions: The assay LoD meaningfully impacts clinical performance of SARS-CoV-2 tests. The highest LoDs on the market will miss a majority of infected patients. Assays should therefore be benchmarked against a universal standard to allow cross-comparison of SARS-CoV-2 detection methods.
Keywords: SARS-CoV-2; antigen detection; cycle threshold; limit of detection; viral load.