Accuracy of UK Rapid Test Consortium (UK-RTC) “AbC-19 Rapid Test” for detection of previous SARS-CoV-2 infection in key workers: test accuracy study

• Published in: BMJ (Online) 2020-11, Vol.371, p.m4262
• Main Authors: Mulchandani, Ranya, Jones, Hayley E, Taylor-Phillips, Sian, Shute, Justin, Perry, Keith, Jamarani, Shabnam, Brooks, Tim, Charlett, Andre, Hickman, Matthew, Oliver, Isabel, Kaptoge, Stephen, Danesh, John, Di Angelantonio, Emanuele, Ades, Anthony E, Wyllie, David H
• Format: Article
• Language: English
• Subjects: Accuracy; Antibodies; Antigens; Betacoronavirus; Bias; Blood & organ donations; Blood donors; Clinical Laboratory Techniques - standards; Confidence intervals; Consortia; Coronavirus Infections - diagnosis; Coronaviruses; COVID-19; COVID-19 Testing; Discordance; Disease transmission; Female; Firefighters; Health Personnel; Humans; Illnesses; Immunoassay; Immunoassay - standards; Infections; Laboratories; Male; Medical diagnosis; Medical personnel; Pandemics; Pneumonia, Viral - diagnosis; Police; Polymerase chain reaction; Predictive Value of Tests; Proteins; Reagent Kits, Diagnostic - standards; SARS-CoV-2; Sensitivity and Specificity; Severe acute respiratory syndrome coronavirus 2; United Kingdom; Workers
• ISSN: 1756-1833; 0959-8138; 1756-1833
• DOI: 10.1136/bmj.m4262

AbstractObjectiveTo assess the accuracy of the AbC-19 Rapid Test lateral flow immunoassay for the detection of previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.DesignTest accuracy study.SettingLaboratory based evaluation.Participants2847 key workers (healthcare staff, fire and rescue officers, and police officers) in England in June 2020 (268 with a previous polymerase chain reaction (PCR) positive result (median 63 days previously), 2579 with unknown previous infection status); and 1995 pre-pandemic blood donors.Main outcome measuresAbC-19 sensitivity and specificity, estimated using known negative (pre-pandemic) and known positive (PCR confirmed) samples as reference standards and secondly using the Roche Elecsys anti-nucleoprotein assay, a highly sensitive laboratory immunoassay, as a reference standard in samples from key workers.ResultsTest result bands were often weak, with positive/negative discordance by three trained laboratory staff for 3.9% of devices. Using consensus readings, for known positive and negative samples sensitivity was 92.5% (95% confidence interval 88.8% to 95.1%) and specificity was 97.9% (97.2% to 98.4%). Using an immunoassay reference standard, sensitivity was 94.2% (90.7% to 96.5%) among PCR confirmed cases but 84.7% (80.6% to 88.1%) among other people with antibodies. This is consistent with AbC-19 being more sensitive when antibody concentrations are higher, as people with PCR confirmation tended to have more severe disease whereas only 62% (218/354) of seropositive participants had had symptoms. If 1 million key workers were tested with AbC-19 and 10% had actually been previously infected, 84 700 true positive and 18 900 false positive results would be projected. The probability that a positive result was correct would be 81.7% (76.8% to 85.8%).ConclusionsAbC-19 sensitivity was lower among unselected populations than among PCR confirmed cases of SARS-CoV-2, highlighting the scope for overestimation of assay performance in studies involving only PCR confirmed cases, owing to “spectrum bias.” Assuming that 10% of the tested population have had SARS-CoV-2 infection, around one in five key workers testing positive with AbC-19 would be false positives.Study registrationISRCTN 56609224.