The Indian Council of Medical Research (ICMR) has issued an advisory for using pooled samples for testing of COVID-19 in order to increase the number of tests conducted by laboratories across the country.

COVID-19 containment measures are pacing up across the country. However, it is argued that we are lagging in the number of tests to be carried out.  With certain limitations, pooled testing promises an edge over individual testings of suspected patients.

What is pooled testing?

• In a pooled testing algorithm, samples of multiple individuals are put together in a tube and screened through the PCR test.
• In case the pooled test turns out to be positive, individual samples are tested, which is referred to as pool de-convolution.
• If there’s no positive result, all individual samples in the pool are regarded as negative, resulting in substantial cost savings.

What the ICMR has recommended?

• ICMR has advised that while more than two samples can be pooled together, the number should not exceed five samples to avoid sample dilution, which can lead to false negatives.
• This method can be used in areas where the prevalence of COVID-19 is low, which means a positivity rate of less than two per cent.
• In areas with a positivity rate between two to five per cent, sample pooling of PCR screening may be considered in a community survey of surveillance among asymptomatic individuals.
• Samples of individuals with known contact with confirmed cases or healthcare workers should not be included in the pooled samples.
• Also, ICMR has said pooling of sample is not recommended in areas or population with positivity rates of over five per cent.

Benefits of pooled testing

• Using this method, substantial costs and testing kits are saved.
• For instance, if a pooled sample consists of the samples of five individuals and it tests negative, the cost of four testing kits is saved and more number of people are covered with fewer resources.
• Significantly, pooled screening can also help in tracking down the asymptomatic cases of the disease, thereby tracking community transmission.
• But in case the sample tests positive, all individuals need to be tested separately.

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