In the COVID-19 pandemic, testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a key tool in limiting spread. A practice article in CMAJ (Canadian Medical Association Journal) outlines five things to know about diagnostic testing for SARS-CoV-2.
- Test sensitivity depends on timing of sample collection – nasopharyngeal testing sensitivity is highest when performed soon after symptoms appear
- Test sensitivity varies according to specimen type and disease severity – in people with infection in the lower respiratory tract, samples taken from lower respiratory tract are more likely to be positive than those taken from the upper respiratory tract (nasopharyngeal).
- A positive test does not always mean infectivity – tests do not report viral load, and samples taken weeks after symptom onset or resolution may detect virus remnants that are unlikely to be infectious.
- Point-of-care testing provides rapid diagnosis but is limited by the inability to test many samples simultaneously
- Positive serology does not mean lifelong immunity – serologic blood tests measure antibodies indicating previous exposure but there are many unknowns.
“Diagnostic testing for SARS-CoV-2” is published June 3, 2020.