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Limit rapid antigen tests to 30-40% of total & only pre-symptomatic cases — Centre to states

In a letter to states, health and health research secretaries have expressed concern over excessive use of rapid antigen tests and quality of testing kits.

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New Delhi: The Centre has in a fresh letter to states expressed reservations about excessive use of rapid antigen tests (RATs) and asked states to restrict the use of the rapid tests to only 30-40 per cent of the total Covid-19 tests.

In a joint letter to states, Health Secretary Rajesh Bhushan and Secretary, Health Research, Dr Balram Bhargava have said: “RATS should be used for diagnosis of pre-symptomatic or early symptomatic individuals where the viral load is expected to be high. Their use in patients who present after 5-7 days of onset of symptoms is not recommended. RATS must not take precedence over RTPCR tests. The use of RATS should be restricted to =<30-40% in the states.”

An analysis by ThePrint last month revealed that 88 per cent of tests conducted in Bihar are RATs, while this figure is 63 per cent for Kerala and 60 per cent for Uttar Pradesh.

Rapid antigen tests are known to be prone to false negatives, which is why protocol mandates that all RAT-negative samples from symptomatic people have to be retested using RTPCR. Experts say it is possible that a rapid antigen test can miss an infection in 50-60 per cent cases.

However, it is cheaper and faster — two facts that have made the test, despite its shortcomings, a preferred option for most states, with the exception of Tamil Nadu.

Last month, when Delhi saw its biggest peak yet, one of the things that the government was asked to rectify was its over reliance on rapid antigen tests.

Also read: Healthcare workers at Covid risk both inside and outside hospitals, US study finds

Concerns about quality of RAT kits

The letter from the two most senior civil servants also flags the possibility of lack of consistency in the quality of RAT kits available currently.

“As per the data available in the ICMR portal, % positivity due to RTPCR is higher than RAT for all states. This could be due to several reasons like inappropriate use of RATS, in the field, batch to batch inconsistency etc. This issue was discussed recently in the laboratory subgroup meeting of the National Task Force for COVID19 at ICMR,” Bhushan and Dr Bhargava wrote.

According to ICMR guidelines, the minimum acceptable criteria for RATs, which are to be used only in the field without being transferred to a laboratory setup, is a minimum sensitivity of 50 per cent and a minimum specificity of 95 per cent.

Sensitivity is a measure of a test’s ability to detect true positives while specificity is its capacity to detect true negatives.

For RATs that are to be performed in a laboratory setting and would therefore need the samples to be transferred in a viral transport medium, the minimum acceptable sensitivity is 70 per cent and the minimum acceptable specificity is 99 per cent.

Till 18 November, the ICMR had validated 50 RAT kits from different companies.

The ICMR has also separately written to RAT vendors to ensure consistency in various batches.

“ICMR has repeatedly advised on use of RATS following the algorithm in the testing strategy of ICMR. The algorithm should be strictly followed by states using RATs to avoid missing of cases. States may explore mechanisms for batch testing of RATS being procured by them,” said the letter dated 9 December.

Also read: Officials told to gear up infrastructure, systems for Covid vaccine rollout by 25 Dec


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