The Philippine Red Cross (PRC), defending the integrity of Covid positive results issued by their Subic laboratory on the samples, acknowledged on Tuesday the possibility of “false positive” results, and stressed that “no test is 100 percent accurate.”
The PRC said that the test methodology and procedures are standardized in all its 13 laboratories across the country, adding that the Research Institute for Tropical Medicine (RITM) sends proficiency test (PT) samples to the lab using a random-blind method.
According to PRC, this control method wherein the RITM sends PRC samples, wherein RITM already knows the results, will be compared with the results that the PRC will issue.
“In such cases, the Department of Health encourages us to err on the side of caution and treat all positive results as true positive. This is designed to protect everyone, including the clients and their families and co-workers. This is especially true for health-care workers who are constantly at risk of exposure to the virus,” the PRC said.
The statement of PRC was issued after President Duterte ordered the DOH to investigate PRC’s RT-PCR test results which reportedly “false positive” results.
The PRC stressed that they are subjected to RITM’s PT every time a laboratory opens. The issuance of the License to Operate by the DOH is dependent on passing the proficiency test with a 100 percent score.
All 13 PRC Molecular Laboratories, the PRC said, obtained a 100 percent score for the proficiency tests they underwent from the time the first molecular laboratory opened in April 2020, and in May 2021 as part of the 2021 External Quality Assurance Program (Post Accreditation) for RT-PCR Detection of SARS COV-2.
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.
It added that the testing samples alluded to in the hearing at the Lower House pertain to samples 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.
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.
“This is an example of a situation where the PRC, on its own initiative and at its own expense, requires an automatic re-run by its molecular labs in order to ensure the accuracy of results. On the second run, the results came out exactly the same. The Subic laboratory followed standard operating procedures and quality assurance guidelines as it has done for all 122,000 samples processed by the Subic lab from July 1, 2020 to September 3, 2021,” the PRC said.
The PRC noted that the timing of tests done relative to exposure to the virus are factors that may produce different results adding that 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.
“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.”
RT-PCR testing remains to be the “gold standard”
The DOH, on the other hand, emphasized that RT-PCR testing remains to be the gold standard for confirming the presence of SARS-CoV-2.
“Moreover, the test kits being used in the country have been evaluated by the Research Institute for Tropical Medicine,” the DOH said.
The DOH said that the outcome of a laboratory test result is influenced by multiple factors, affecting all the phases of testing from pre-analytic, analytic to post-analytic (from specimen collection, specimen transport, specimen evaluation, nucleic acid extraction, testing, results analysis, verification and releasing).
Additionally, the DOH said it is possible for test results from the same case collected from two different time points to vary, potentially due to the timing of specimen collection, depending on the clinical course of infection, and other possible sources of variation in the pre-analytical, analytical and post-analytical phases.
“All tests have to be interpreted using the epidemiological and clinical situation of the patient,” the DOH concluded.
Image credits: Bernard Testa