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Red Cross: Timing of specimen collection, sampling method factors in ‘false positive’ results

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The Philippine Red Cross on Tuesday explained the reason behind the supposed false positive results of COVID-19 specimens, which was previously raised in a congressional hearing.

The Research Institute for Tropical Medicine earlier said it is looking into an incident in Subic where some hospital personnel tested positive for the virus but a retest three days later tested negative.

During the hearing, House Deputy Speaker and SAGIP party-list Representative Rodante Marcoleta said 49 health personnel yielded positive for COVID-19 but after a second test in a different laboratory, 44 of them tested negative.

In response, the humanitarian organization said the samples were taken at the Unihealth-Baypointe Hospital and Medical Center in Subic Bay Freeport Zone by their personnel and tested at the PRC Molecular Laboratory also in Subic Bay Freeport Zone.

But Red Cross said even after their laboratory conducted a re-run of the tests, the results came out the same.

"Of the 48 samples, 45 turned out positive, triggering a complete re-run and a manual process to eliminate the possibility of erroneous results, which may be caused by cross-contamination," it said in a statement.

"On the second run, the results came out exactly the same," it further pointed out.

Moreover, Red Cross said the "timing" and collection of second samples may have triggered the negative results. It said the personnel may have already been negative for the virus when the second samples were collected by the other laboratory.

"The timing of tests done relative to exposure to the virus are factors that may produce different results. The negative result of the tests in question came from specimens collected after three days, which may be one such factor for the negative result," Red Cross said.

"Clients may have truly been negative already by the time their second sample was taken. The sampling method (in this case, sampling was performed by Baypointe Hospital personnel), test kits, extraction method, and the thermocycler (PCR machine) used by the testing laboratory are also factors that may influence the results," it added.

Nonetheless, Red Cross "acknowledged" the possibility of false positive test results as there is no perfect COVID-19 test method.

"While we strongly stand by the integrity of the positive results issued by our Subic laboratory on the samples, we acknowledge the possibility of false positive results since no test is 100% accurate," it said.

Also, Red Cross assured that all its 13 laboratories passed the standards of Research Institute for Tropical Medicine and received a license to operate from Department of Health.

"This test and the strict implementation of quality standards in all PRC laboratories based on protocols set upon by manufacturers, in line with the standards set forth by the DOH and the RITM, assure the public of the accuracy of test results released by PRC," said Red Cross.

Health Chief Francisco Duque III said the RITM is already looking into the  reported inaccurate results of the COVID-19 tests.

In his Talk to the People on Monday night, President Rodrigo Duterte also ordered DOH to launch a probe into the  alleged false positive test results of PRC, headed by Senator Richard Gordon. 

Duterte made the pronouncement in the wake of his attacks against Gordon, who is currently leading the Senate hearing on "overpriced" COVID-19 procurement by the government. Duterte had consistently denied that the supplies were highly expensive and corrupted.—LDF, GMA News

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