Question reference: S5W-33594
- Asked by: Alexander Burnett, MSP for Aberdeenshire West, Scottish Conservative and Unionist Party
- Date lodged: 30 November 2020
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Current status: Answered by Jeane Freeman on 7 January 2021
Question
To ask the Scottish Government at what level of population infection will the COVID-19 testing strategy change from maximising sensitivity to find every possible case in high-volume throughput laboratories to a focus on maximising specificity in low-volume laboratories with high levels of quality control in order to avoid any risk of false positive over-diagnosis and a pseudo epidemic.
Answer
No laboratory test is 100% accurate. The laboratory tests being used to detect the SARS-CoV-2 virus in Scotland are real-time RT-PCR (Reverse Transcription Polymerase Chain Reaction) assays which are the gold standard for respiratory viruses.
The likelihood of false positives arising is dependent on a number of factors such as the overall prevalence of infection in the population, the clinical presentation of disease in the person sampled, and quality of the sampling method.
NHS Scotland Laboratories have a protocol in place to carry out confirmation testing (or repeat testing) in certain circumstances to confirm whether low positive test results should be reported as positive or negative. Public Health Scotland have produced guidance for sampling and laboratory investigations to minimise reporting of false positives occurring: https://www.hps.scot.nhs.uk/web-resources-container/covid-19-guidance-for-sampling-and-laboratory-investigations
UK Government Laboratories (Lighthouse) also have similar quality procedure systems in place to minimise false positives but are unable to repeat test low positive results.
A clinical and Scientific Review of our testing strategy was published on 23 October in light of the latest evidence of the state of the epidemic in Scotland and the latest understanding of testing capacity and demand forecasts in the next three months. We will continue to keep our testing strategy under review in line with the changing nature of the epidemic in Scotland. Further information on the review of the strategy can be found here:
https://www.gov.scot/news/clinical-and-scientific-review-of-testing/