Rapid chromatographic immunoassay-based evaluation of COVID-19: A cross-sectional, diagnostic test accuracy study & its implications for COVID-19 management in India

Abstract

Background & objectives: Coronavirus disease 2019 (COVID-19) has so far affected over 41 million people globally. The limited supply of real-time reverse transcription-polymerase chain reaction (rRT-PCR) kits and reagents has made meeting the rising demand for increased testing incompetent, worldwide. A highly sensitive and specific antigen-based rapid diagnostic test (RDT) is the need of the hour. The objective of this study was to evaluate the performance of a rapid chromatographic immunoassay-based test (index test) compared with a clinical reference standard (rRT-PCR).

Methods: A cross-sectional, single-blinded study was conducted at a tertiary care teaching hospital in north India. Paired samples were taken for RDT and rRT-PCR (reference standard) from consecutive participants screened for COVID-19 to calculate the sensitivity and specificity of the RDT. Further subgroup analysis was done based on the duration of illness and cycle threshold values. Cohen's kappa coefficient was used to measure the level of agreement between the two tests.

Results: Of the 330 participants, 77 were rRT-PCR positive for SARS-CoV-2. Sixty four of these patients also tested positive for SARS-CoV-2 by RDT. The overall sensitivity and specificity were 81.8 and 99.6 per cent, respectively. The sensitivity of RDT was higher (85.9%) in participants with a duration of illness ≤5 days.

Interpretation & conclusions: With an excellent specificity and moderate sensitivity, this RDT may be used to rule in COVID-19 in patients with a duration of illness ≤5 days. Large-scale testing based on this RDT across the country would result in quick detection, isolation and treatment of COVID-19 patients.

Keywords: Antigen test; COVID-19; SARS-CoV-2; point-of-care test.

Fig. 1

A plot of the post-test probability against the pre-test probability of having COVID-19. The green and orange ribbons represent the 95% confidence interval around these values. The vertical line indicates the pre-test probability or prevalence of COVID-19 (23.3%). Where this vertical line cuts the green and orange lines, those points give the probabilities that if the result of the rapid diagnostic test is negative, then COVID-19 is absent, and if the result is positive, the disease is present.

Fig. 2

A plot comparing cycle threshold (Ct) values of true-positive and false-negative cases and rRT-PCR-positive test results. The X-axis represents Ct values and the Y-axis represents the number of rRT-PCR-positive test results. The data table below the X-axis shows true-positive and false-negative rapid diagnostic test results.