Diagnostic performance of rapid antigen test for COVID-19 and the effect
of viral load, sampling time, subject's clinical and laboratory
parameters on test accuracy
Abstract
The ongoing COVID-19 pandemic has highlighted the central role of
diagnostic tests in pandemic control. Although reverse transcriptase
quantitative real-time PCR (RT-qPCR) is the gold standard for the
diagnosis of COVID-19, several rapid antigen tests (RAT) have been
commercialized as rapid point-of-care diagnostics. To the best of our
knowledge, there are limited data on the effect of patient’s clinical
and laboratory parameters on RAT performance and no studies exist that
tested the importance of combining laboratory measurements in patient’s
blood in enhancing the performance of RAT. Here we tried to fill these
gaps by evaluating the diagnostic performance of the RAT “Standard ™ Q
COVID-19 Ag” in participant’s subgroups studying the influence of viral
load, sampling time-post symptoms, clinical and laboratory features on
test performance. Eighty-three nasopharyngeal and oropharyngeal swabs
were tested for sever acute respiratory syndrome-coronavirus 2
(SARS-CoV-2) by both RT-qPCR and RAT. Diagnostic accuracy of the RAT was
evaluated for participant’s subgroups that have various features.
Support vector machine model was then used to investigate whether
laboratory measurements in subject’s blood would enhance the predictive
accuracy of this RAT. The sensitivity, specificity and accuracy of the
RAT were 78.2, 64.2 and 75.9%, respectively. Samples with high viral
load and those that were collected within one week post-symptom showed
the highest sensitivity and accuracy. Measuring Laboratory indices did
not enhance the predictive accuracy of this RAT. It is concluded that
“Standard ™ Q COVID-19 Ag” should not be used alone for COVID-19
diagnosis due to its low diagnostic performance. This RAT is best used
at early disease stage and in patients with high viral load.