Indian researchers develop new low-cost RT-nPCR test for coronavirus detection

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Researchers at the Centre for Cellular and Molecular Biology (CCMB) have developed a new test to detect coronavirus named reverse transcription nested PCR (RT-nPCR) test based on a low-cost and low-tech model, said a Thursday release from union science and technology ministry.

The main Covid testing protocol currently sanctioned by the Indian Council of Medical Research (ICMR) is called RT-qPCR tests, which expands to mean reverse transcription polymerase chain reaction (RT-qPCR) and according to the ministry, the newly developed test has given comparable results with the standard RT-qPCR test.

“This test does not require real-time quantitative RT-qPCR. The RT-nPCR developed by the CCMB research team has shown comparable performance to the standard RT-qPCR test. The nested PCR (RT-nPCR) approach does not depend on RT-qPCR but uses standard RT-PCR as part of an endpoint assay,’’ a statement from the ministry said of the new testing protocol.

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While comparing the results of both types of tests, researchers found that the standard RT-qPCR test can have low detection efficiency-- less than 50%--in a real testing environment. It was attributed sometimes to low viral load in many samples. The new RT-nPCR test was able to make positive detections even in samples found to be negative in two RT-qPCR tests, the statement says.

“It also detected 13% samples as positive among samples that were negative by the standard RT-qPCR test (likely false negatives). Based on the experimentally measured false negative rate by RT-nPCR tests from this study, it was estimated that as many as 50% of positive samples may escape detection in single pass testing by RT-qPCR in an actual testing scenario,” the statement from the ministry states.

It must be added though that RT-nPCR test was able to identify 90% of the positive samples detected together by both standard RT-qPCR tests.

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The experiment was conducted using the RNA isolated from nasopharyngeal swab samples previously tested using one of the two RT-qPCR tests.

“This finding brought home the importance of monitoring detection efficiency directly in test environments,” the ministry says.

This new test is awaiting approval from ICMR and the lab that developed the new test says that RT-nPCR test could be deployed in those places where RT-qPCR test machines are not available.

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