‘Time-dependent’ PCR tests better suited for targeted testing — expert

It is better to focus on targeted COVID-19 testing rather than mass testing because the accuracy of polymerase chain reaction (PCR) tests vary over the course of infection, an expert said Tuesday.

Infectious disease expert Dr. Edsel Salvana said even if an individual contracts COVID-19, it would take about three days for them to test positive through PCR.

“And even then, there is only a 33% possibility that you would test positive,” he said in a mix of English and Filipino during a Palace briefing.

Salvana explained that the accuracy of a PCR test increases to 62% once the individual has developed symptoms, usually on the fifth day of infection.

On the third day of having symptoms, the PCR test would show about 80% sensitivity to COVID-19 “and then it starts to go down after that.”

“If you test someone without thinking about the timing or symptoms, you are in danger of clearing someone 2 out of 3 times who has COVID but is negative on RT-PCR,” Salvana warned.

“Because our tests are not perfect and are time-dependent, it is important to time the tests properly and to test the right people.”

There have been renewed calls for mass COVID-19 testing as the country grapples with a fresh surge in infections. 

The Department of Health earlier maintained that “risk-based” testing is more efficient than widespread testing. 

The government has also unveiled a plan to increase testing to 90,000 daily through the use of antigen test kits. 

The Philippines has 143,726 active cases as of Monday afternoon. — RSJ, GMA News