In a breakthrough for Covid-19 diagnostic testing, Indian Council of Medical Research (ICMR) has stated that a throat and nose swab test, which shows results within 15 to 30 minutes of sample collection from suspect individuals can be employed in field level settings.
ICMR has stated that a new test, Standard Q COVID-19 Ag detection kit, which is manufactured by South Korean-based SD Biosensor in its Manesar unit of Gurugram, is the only available standalone antigen detection assay which is reliable, currently.
This is second only to the gold standard lab-based reverse transcription polymerase chain reaction (RT-PCR) tests which are currently largely used in detection of the virus and are DNA-based tests.
What is the new test all about
The new antigen assay recommended by ICMR also tests the virus from the nose and throat swabs. After the sample collection, swab is immersed and squeezed in a customised viral extraction buffer provided with the kit, which inactivates the virus thereby reducing biosafety hazards, ICMR has said.
The scientists have also observed that once the sample is collected, it is stable only for one hour, therefore the antigen test needs to be conducted at the site of sample collection in the healthcare setting. After 15 minutes, the test can be interpreted as positive or negative, by the appearance of test and control lines, which can be read with naked eye, requiring no specialised equipment. The maximum duration for interpreting the test is 30 minutes. ICMR has said that the test kit can be stored between 2 degree celsius to 30 degree celsius.
ICMR recommendations
ICMR has recommended it’s use of as a point of care diagnostic assay in combination with gold standard RT-PCR test, in containment zones and hotspots, where it can be performed on all influenza-illness patients, all patients without symptoms which are direct and high risk contacts with co-morbidities like lung, heart, liver, kidney, diabetes, neurological and blood disorders to be tested between day five and ten of coming in contact with a positive patient.
In hospitals, those patients undergoing chemotherapy, immunosuppressed patients including those with HIV, organ transplant candidates, elderly patients, those who want neurosurgery, Ear Nose Throat or dental procedures, and even non surgical procedures like bronchoscopy, endoscopy and dialysis can be offered this test.
“Those suspects that test negative through rapid antigen test should undergo RT-PCR to rule out infection, whereas those who show a positive test should be considered true positives and do not need reconfirmation by RT-PCR test,” ICMR guidelines state.
The test was evaluated at Indian Council of Medical Research and All India Institute of Medical Sciences in New Delhi. ICMR has claimed that the test has very high specificity which means it has a high ability to detect true negative samples - up to 99.3 to 100 per cent at two sites. Sensitivity, which is the ability to detect true positive samples correctly, ranged from 50.6 per cent to 84 per cent, depending on viral load of the patient.