Antibody testing can help in monitoring of COVID-19 infections – ex-DOH chief

MANILA, Philippines — The antibody test may not be considered as the “gold standard” procedure for detecting SARS-CoV-2, which causes the coronavirus disease (COVID-19), but it can still improve the local government units’ (LGUs) efforts to trace and treat patients infected with the respiratory disease.

Former Health Secretary Esperanza Cabral said the antibody test would not be a waste of time despite not being a stand-alone test like the reverse transcription polymerase chain reaction (RT-PCR) test.

“It can tell you how many people have been exposed to SARS-COV-2 and have developed antibodies to it in a certain population, and the tracker, through time, can tell you if there is continuing transmission in that population or not,” Cabral said.

According to the Department of Health (DOH), an antibody test will tell individuals if they have a past infection, but it doesn’t provide information on current infection.

The antibody test calls for collecting serum, or the liquid part of the blood. But DOH says an RT-PCR test will have to be done for confirmation.

In Pasig, health workers conduct free enhanced chemiluminescence immunoassay (ECLIA) antibody testing for residents, which detects antibodies in blood specimens.

Manila uses serology machines of Abbott Laboratories, which is based in the US, to augment its community-based testing through mobile, walk-in, and drive-through facilities.

Choose the best antibody test

With thousands of rapid antibody tests in the market, Cabral gave advice on selecting a test kit.

“They need to choose the most efficient rapid antibody test to increase their confidence level,” Cabral said in Filipino in a phone interview.

“The most important thing: You have to make sure that the rapid antibody test has the highest sensitivity and specificity as possible,” she added.

According to the Medical City in Pasig, sensitivity refers to the proportion of patients compared to the total who have the disease who yield a reactive test result. Meanwhile, specificity refers to the proportion of patients without the disease who yield a non-reactive test result.

Cabral said the higher rate of sensitivity and specificity, the higher the confidence interval in testing a big population. The confidence interval is the range that one is sure (usually at 95% confidence) that the test characteristics will fall within it.

ECLIA testing is more reliable than most rapid tests because it has 100 percent sensitivity and specificity.

According to Abbott, its testing machines have an accuracy rate of 99.6-percent. However, confirmatory swab tests are still required under public health protocols.

Follow proper procedure

Selecting the right antibody test is not enough. The proper use and timing of the test must be followed for accurate testing, Cabral said.

“The rapid anti-body test must be used efficiently and the person who will do it must know how to interpret it.,” she said.

She pointed out that doing the test in the early stage of the infection would produce false-negative or false-positive results.

She recommended that the test be conducted eight days after a patient’s exposure to the virus.

As of Saturday, Sept. 12, the Philippines logged a total of 257,863 including 187,116 recoveries and 4,292 deaths.

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