Coronavirus: After govt nod, Delhi hospitals start antigen testing
Samples, however, will not be collected from homes for the antigen test as they need to be processed within an hour of collection. An antigen is a foreign molecule that induces an immune response in the body, especially the production of antibodies, and detecting its presence determines a present infection.Updated: Jul 04, 2020 02:01 IST
In a bid to scale up testing and measure the spread of the coronavirus pandemic in Delhi, government and private hospitals in the capital have begun testing for Covid-19 using the antigen-based method following the state government’s nod.
Samples, however, will not be collected from homes for the antigen test as they need to be processed within an hour of collection. An antigen is a foreign molecule that induces an immune response in the body, especially the production of antibodies, and detecting its presence determines a present infection.
“We started the antigen testing from Wednesday. The selection criterion depends on how quickly the results are needed as it is quicker than the RT-PCR test. If there’s time in hand, then we prefer testing through RT-PCR because if an antigen test is negative, one has to repeat the test through an RT-PCR,” said Dr Anupam Sibal, group medical director, Apollo Hospitals.
The Indian Council of Medical Research has validated the point-of-care antigen method for Covid-19 diagnosis, which can be used in containment zones, hot spots and hospitals. The test can give results in maximum 30 minutes compared to five hours in the conventional real-time polymerase chain reaction (RT-PCR) test.
The Delhi government also started rapid antigen-based testing on June 18. So far, the exercise was confined to containment zones but on Friday it was expanded to other areas across all 11 revenue districts. Till Thursday, around 150,000 people were tested through antigen kits. The positivity rate is around 7.5%, said a senior government official.
No testing numbers were readily available for the hospitals.
Apart from Apollo, other corporate hospitals such as Max Healthcare and Ganga Ram Hospital have begun antigen tests. “This is a naso-pharangial swab test like in RT-PCR that detects current infection in symptomatic and asymptomatic patients. This is quick and a lot cheaper. But we carry out an RT-PCR gold standard test for confirmation in case the result is negative,” said Dr Poonam Das, chief of pathology, Max Labs.
The antigen test has high specificity (true negative rate) of 99.3% to 100%, which rules out people who are not infected. Tests with high specificity are most useful when the result is positive. Sensitivity (true positive rate) is lower at 50.6% to 84%, which makes it less accurate in correctly diagnosing a positive case. This is why people who test negative, especially those with symptoms, have to undergo an RT-PCR test to rule out active infection.
The deadline for sample processing makes the test more feasible as a hospital-based testing modality. Private stand alone laboratories are, however, still contemplating on whether to start, and how to start, antigen testing.
“Even though the government has allowed antigen testing, we haven’t started it as we are figuring out the modalities. For hospitals, it is more feasible because you are collecting samples on the spot and can send for processing almost immediately. If at all we decide to do antigen testing, then it has to be through our drive-thru facilities and not home collection,” said Sanjeev Vashishta, managing director and CEO, Pathkind Diagnostics.
A representative of another private laboratory, agrees, “When I send a person for home collection, they collect a few samples together. In case of antigen tests, the sample has to be processed within an hour and I can’t be sure if my phlebotomist is back in time. After an hour, the sample will go bad, which is why it is called a point-of-care test.”
Availability of kits is another problem for labs as only one company’s kits have been validated so far.
The kit— Standard Q COVID-19 Ag detection kit—has been developed by SD Biosensor, a South Korea-based company, and jointly validated by ICMR and All India Institute of Medical Sciences, Delhi. The Central Drugs Standard Control Organisation has also approved its import and manufacturing in the country.
“We can produce almost two lakh testing kits in a day,” said CS Bedi, medical advisor, SD Biosensor.
Labs say placing a bulk order is a problem as only one company is supplying all kits and demand is huge. “Even though we are getting the orders we placed, still I would say these kits are in short supply,” said a hospital source from Fortis Health care. Fortis is in the processes of procuring kits and will start antigen testing soon.
Government hospitals are also beginning to conduct the test. “We have started antigen testing for Covid-19 in our hospital last week,” said Dr Randeep Guleria, director, All India Institute of Medical Sciences (AIIMS), Delhi.
The eligibility for performing antigen testing is the same as that for RT-PCR test. The most important requirement is a valid prescription from a registered doctor, an ICMR form that your doctor will fill in and a government identity proof. The test result can be collected the same day.
“We follow ICMR guidelines for testing. For antigen based-testing, it is the same,” said an official at Ganga Ram Hospital, who did not wish to be identified.
Most hospitals are accepting walk-ins for tests if there is a valid prescription. Those without a prescription will be directed to the hospital’s fever or flu clinic where a doctor will assess the person and prescribe a test, if required.
The antigen test cost is around ₹1,000 for a test compared to Rs 2,400 for the RT-PCR test.
ICMR has advised states to use the antigen kit for Covid-19 diagnosis in containment zones, hot spots, and hospitals to test all symptomatic influenza-like illness, asymptomatic direct and high-risk contacts with co-morbidities, and asymptomatic high-risk patients who are hospitalised or seeking hospitalisation.
High-risk patients include those undergoing chemotherapy, immunosuppressed patients, including HIV positives, suffering from a malignancy, transplant patients and elder patients with co-morbidities.
The test has also been allowed in asymptomatic patients undergoing aerosol generating surgical or non-surgical interventions such as neurosurgery, ear nose throat surgery, dental procedures, bronchoscopy, upper gastro-intestinal endoscopy and dialysis.
“It is a slightly crude test when compared with RT-PCR. The RT-PCR detects the RNA of the virus. Antigen tests what you call is the wall of the virus, but what works in its favour is that it is quicker and does not require too much technical expertise for performing the test. It’s a good alternative,” said Dr GC Khilnani, former head, pulmonology department, AIIMS, Delhi.