Interesting LFT study18 Apr 2021 11:58
https://twitter.com/BQuilty/status/1383437545296470026?s=19
Findings Most of the rapid antigen LFDs showed a high specificity (>98%), and accurately detected 50 PFU/test (equivalent N1 Ct of 23.7 or RNA copy number of 3×106/ml). Sensitivities of the LFDs performed on clinical samples ranged from 65 to 89%. These sensitivities increased in most tests to over 90% for samples with Cts lower than 25. Positive virus culture was achieved for 57 out of 141 samples, with 80% of the positive cultures from swabs with Cts lower than 23. Importantly, sensitivity of the LFDs increased to over 95% when compared with the detection of infectious virus alone, irrespective of Ct. Longitudinal studies of PCR-positive samples showed that most of the tests identified all infectious samples as positive, but differences in test sensitivities can lead to missed cases in the absence of repeated testing. Finally, test performance was not impacted when re-assessed against swabs positive for the dominant UK variant B.1.1.7.
And from our initial CV
30 positive samples were tested with Ct values of 26 and below, with half of those in the range 22-26, and the lateral flow test identified 29/30 of these correctly as positive. This indicates a clinical sensitivity of 96.7% for samples with a Ct value below 26. Importantly, out of a total of 26 negative samples tested with the lateral flow device, the test correctly identified all 26 as negative, giving a clinical specificity of 100%.