India has ordered a pause in testing for antibodies to the coronavirus because of concerns over the accuracy, the country's health officials said on Wednesday, complicating the fight against the pandemic as its tally of cases nears 20,000.

India trails many countries in conducting the standard swab tests to determine the presence of the novel coronavirus because of limited testing equipment and protective gear for medical workers.

Early this month, health authorities approved blood tests for coronavirus antibodies as a faster way to bolster the screening effort and they ordered more than a half billion testing kits from China.

But the chief of epidemiology at the Indian Council of Medical Research, Dr RR Gangakhedkar, said he had asked health authorities to temporarily stop the tests for antibodies because of conflicting results.

“This is a first generation test developed in just three-and-a-half months and needs refinement, the variations cannot be ignored,” he said.

Federal health experts have been sent to help authorities in states to validate the equipment.

“We have advised the states not to use them for the next two days until we come out with an advisory,” he said.

The antibody tests do not always pick up early stage infections but show whether a person had the virus in the past, even if the person had no symptoms of Covid-19, the disease caused by the novel coronavirus.

In comparison, the swab test, known as the RT-PCR-technology swab test, determines whether a person has the virus at that moment by looking for it in nose or throat secretions.

The health minister of the western state of Rajasthan said the two tests were in some cases producing conflicting results, raising doubts reliability.

“The kits were used for testing of patients who have already tested positive for coronavirus,” the state minister, Raghu Sharma, said.

“But the rapid test kits found them negative, which raised questions about the credibility of these kits.”

Both tests are seen as critical in the coronavirus fight, but antibody tests are a relatively cheap, fast means to sort populations into risk groups and measure the spread of the virus.

India has detected 19,983 cases of the coronavirus, after an increase of nearly 1,000 cases in one day, according to the government data.

There have been 640 deaths, still a small number compared with tolls in many other countries but officials say the infections could rise once a nearly six-week lockdown is lifted on May 3.

Big cities of Delhi and Mumbai and their adjoining areas have taken the brunt of the infection, leaving the countryside less affected.