Researchers from AIIMS in Delhi have concluded that the rapid antigen test showed an excellent specificity to ‘rule-in’ Covid-19 patients within the first five days of illness with a moderate sensitivity.
The overall sensitivity and the specificity of the test was 81.8 percent and 99.6 percent respectively, and the test accuracy was 95.4 percent. The sensitivity of the test was higher (85.9 percent) in participants with the duration of illness lesser than five days, said the cross-sectional study published in the Indian Journal of Medical Research.
The study was done on 330 patients admitted at AIIMS, Delhi, between May 31 and July 24. Researchers included symptomatic patients and asymptomatic/pre-symptomatic contacts of laboratory-confirmed cases with exposure between 5 and 10 days.
“The analytical performance…depends on the mixing of NP swab with buffer and the viral load in the sample, but clinical performance of the test may be variable which depends on the technique of sample collection and duration of illness of patients. Hence, the sensitivity will be average in asymptomatic patients because it is difficult to analyze pre-test probability in asymptomatic patients,” stated the paper.
Of the 330 participants, 77 were RT-PCR positive for Covid-19. Sixty-four of them also tested positive in the rapid antigen test. The most commonly presented symptoms among screened participants were fever (31.5 percent), cough (25.4 percent), fatigue/malaise (11.8 percent), headache (3.3 percent) and runny nose (3.3 percent). As many as 57 participants presented with sore throat but only two of them (3.5 per cent) had Covid-19.