A Closer Look at COVID-19 Diagnostic Testing

Posted by Riva Zheng on

Molecular versus Antigen Tests

  1. Molecular tests detect the genetic material or nucleic acid present inside a virus particle. The FDA has authorized molecular tests for use in a clinical laboratory setting and authorized some for use in a POC setting. Most molecular tests are polymerase chain reaction (PCR) tests, also called nucleic acid amplification tests (NAAT). In PCR testing, a machine located in a laboratory or at a POC, depending on the test, runs a series of reactions. These reactions first convert the virus’s ribonucleic acid (RNA), if present, into deoxyribonucleic acid (DNA) and then amplify it (make millions of copies of the DNA); the test then detects this DNA. By running multiple amplification cycles, a PCR test can sense even low levels of viral genetic material in a patient’s sample, so these tests tend to be highly sensitive (especially laboratory PCR tests).
    • A PCR test can be authorized to run batched or “pooled” patient samples if the developer demonstrates that the test meets the EUA standard for pooled testing. If a pooled sample tests positive, the samples that were combined then need to be tested individually to identify the positive case(s). When there is a low prevalence of cases (and a high number of negative results is therefore expected), pooling samples may result in fewer tests needing to be run and fewer testing supplies being required.
  2. Antigen tests detect one or more specific proteins from a virus particle. All currently-authorized antigen tests are POC tests and provide results in less than an hour. Antigen tests tend to be highly specific but are typically less sensitive than molecular tests. However, because antigen tests can generally be produced at a lower cost than molecular tests and have a simpler design, antigen tests could scale to test millions of individuals per day.

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