The basis of rapid diagnostic test kits is either to detect binding of surface protein (antigen) of coronavirus in the throat swab of patients with specific antibody that was already tagged in strip paper resulting in a visible signal or to detect binding of induced antibody (protein) in patients’ blood sample with COVID-19 protein (antigen) that was already tagged in test strip resulting in visible signal. The test is simple, cheap, rapid, takes less than one hour (whereas confirmatory test RT-PCR takes one to two days) and can be carried out in any outdoor settings.
WHO and US CDC still did not approve these rapid kits for diagnostic tests for COVID-19 but recommend for use in surveillance purpose and encourage for continuing research for further improvements that have already resulted in improved versions. Here are some arguments, if approval of rapid test kits can be considered in the present context of COVID-19 situation in Bangladesh.1. Approval of rapid kit should be given, not for diagnostic and treatment purpose, but for use as a triage in outpatient department only to screen positive cases whose throat swabs should be sent for molecular diagnostic confirmation thereby reducing the load in RT-PCR lab.
2. Rapid test kits can be used as an adjunct in patients in whom successive RT-PCR tests are negative or inconclusive.
3. Rapid diagnostic kits can be carried out on people of over-crowded areas viz. in garments factory, slum dwellers and market places where social distancing does not work to see the rate of community transmission.
4. Most importantly rapid test kits can be applied in the community level to see the seroconversion rate due to natural COVID-19 infection thereby selecting groups to whom vaccine will be effective that hopefully will be available in near future.
5. Although rapid test kits has got diagnostic limitations (in 30 to 40 per cent cases results may be false negative) still it has utmost importance in country like Bangladesh. Sensitivity of RT-PCR tests varies from lab to lab,maximum upto 70 per cent but specificity is 100 per cent.
6. Rapid diagnostic tests becomes positive at the end of first week of illness (3 to 7 days) and thereafter when there is limited scope of interventions as at that time patient may have already infected others or fully recovered or rarely may have succumbed tragic death.7. Some governments have suggested that detection of antibodies against SARS-CoV-2 the causative agent of COVID-19 acts as a basis for "immunity passport" or risk free certificate that will enable the individual to travel abroad or return to work but till now there is no evidence that the antibody detected protects against reinfection.
Dr SudeshRakshit, Associate Professor
and Head, Dept. of Pediatrics Jashore