Explainer: COVID-19 Tests

Testing for COVID-19 is essential to containing the virus because it allows governments and healthcare professionals to understand the range and depth of infections in communities. High volumes of testing help outline more effective policies to protect the public from the pandemic. There are three major types of tests used for Covid-19.

By far the most common test used to detect the SARS-CoV-2 virus in COVID-10 patients is the Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) test. RT-PCR tests start with a sample taken from the nose or throat that must be transported to a facility for testing. In places like the Philippines, a limited number of approved laboratories to send test assays is more of a bottleneck than test kits themselves. RT-PCR testing is a multistep process that can detect the presence of viral RNA. They accurately return positive results approximately 71% of the time.

Serological tests are just now becoming available, an immunoassay test which detects antibodies or antigens linked to viral presence in samples. Immunoassay tests produce results much faster than RT-PCR tests (some within 15 minutes). These tests are simpler to use but can return false negatives if administered too early. The FDA recommends using serologica antibodyl tests no earlier than five days after the onset of symptoms, the time required for a COVID19 patient to produce detectable levels of antibodies. Where PCR tests only reveal whether a patient has COVID-19 when they were tested, serological tests can reveal whether someone has had COVID-19 in the past.

Currently, WHO and CDC guidelines say that antibody tests should not be used to diagnose COVID-19 cases. However, there are many places where hard lockdowns pose significant logistics challenges in delivering PCR assays to labs – which, we have already noted, can be few and far away. As they become more accurate and available, antibody tests (used correctly) might be the only realistic diagnostic tool in much of Southeast Asia. 

The last form of diagnostic test to identify COVID-19 in patients is a CT scan. Physicians in Wuhan found that the “sensitivity of CT for COVID-19 infection was 98%”. CT scans are incredibly accurate for diagnosis, but require special equipment and trained staff. Additionally, patients have to be physically on site for the tests to be conducted. These factors make them ill-suited for testing at scale.

COVID-19 CT Scan

Many governments have had difficulty sourcing test kits and are hoping to increase testing capacity through donations and purchases from China. Authorities will need to balance immediate need, test kit reliability, and the capacity of their medical infrastructure when developing plans for using these donated kits. Countries like the Philippines (which as of March 30th have only 5 labs approved for RT-PCR testing) should consider screening with immunoassay tests at scale to reduce the burden on RT-PCR labs and CT scanners. When combined with social distancing, case backtracking, and other measures it could help contain the virus and return life to normal. 

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