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Nose and throat swab polymerase chain reaction (PCR) testing can miss up to 50% of coronavirus disease 2019 (COVID-19) cases, in part because the virus may have already cleared the upper respiratory tract. But by then, patients may have developed antibodies against the virus. An approach that combines rapid PCR and antibody testing could help physicians quickly diagnose more cases, a recent small study of hospitalized patients with suspected COVID-19 suggested.
A University of Cambridge–led team analyzed previously collected data from the COVIDx Study, in which they clinically validated a simple amplification-based assay known as SAMBA II, a rapid PCR test to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Developed by a Cambridge spinoff company with partial US National Institutes of Health funding, the point-of-care (POC) test is now in routine clinical use in the UK.
In the new analysis, the researchers also included stored sera from a subset of 45 patients, which allowed for antibody testing. They collected the patients’ swabs and sera samples a median of 7 days after their symptoms emerged. About half of this group had COVID-19.
The SAMBA II missed about 1 in 5 positive cases based on a reference standard that combined laboratory-based PCR and neutralizing antibody testing. But when the researchers combined the SAMBA II results with those from either of 2 rapid lateral flow antibody assays, the positive predictive value increased to 100%.
The POC antibody tests had 100% negative predictive agreement with the laboratory-based neutralizing antibody test in a separate analysis of fresh finger prick blood from 128 patients with suspected COVID-19 who were not part of the COVIDx Study. Importantly, the assays detected antibodies induced by a now-dominant SARS-CoV-2 variant that wasn’t widespread when the tests were developed.
“[R]apid combined testing could be important in diagnosis and management of COVID-19,” the authors wrote in Cell Reports Medicine. “We envisage a deployment approach whereby both test samples, finger prick whole blood and nose/throat swab, are taken at the same time on admission to hospital.”
Abbasi J. Combining Rapid PCR and Antibody Tests Improved COVID-19 Diagnosis. JAMA. 2020;324(14):1386. doi:10.1001/jama.2020.19129
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