Covid-19: False positives caused by lab’s improper calibration, missed steps during testing

SINGAPORE — The dozens of “false positives” for Covid-19 that turned up in recent days were the result of a test kit that was “not optimally calibrated” in a laboratory, an official from the Ministry of Health (MOH) said.

Associate Professor Kenneth Mak, director of medical services at the ministry, said that this caused the test results to be interpreted incorrectly. Some of the required testing steps were also “not completely followed through”, he added.

“If (the steps had been followed), we would have picked up these (false positive) results earlier,” he said on Tuesday (May 12) at the press conference held by the governmental task force handling the Covid-19 crisis. This was in response a question on whether the errors were due to human mistakes.

The cases were eventually picked up by a “quality assurance programme” that is in place.

The lab, which has not been identified so far, has also enlisted the support of vendors that have provided the test kits and testing equipment to ensure that the tests are being done properly.

“I am confident that they will be able to correct this quickly… (so that) the laboratory can come back on stream to provide its full test capacity for us to meet the desired test rate that we want to carry out the testing strategy,” Assoc Prof Mak said.

In the meantime, the task force has put together some advisories and guidance that lay out the standard process needed to produce accurate tests, he added. These advisories will be sent to all laboratories.

Last Sunday, MOH revealed that one laboratory had tested 33 cases to be positive, but a re-test by the National Public Health Laboratory later found these tests to be false positives.

The false positives, as well as another two equivocal cases that were also later found to be negative, were removed from the total tally of cases on Monday.

On the details of the false positive cases, including whether they included foreign workers and whether they were admitted to the care facilities, Assoc Prof Mak said that the information was unavailable for now.

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