COVID-19 Testing: PCR or Antigen (Rapid) Test

  PCR Antigen (Rapid)
What it tests for Molecular material from the virus is magnified through polymerase chain reaction (PCR) Proteins from the surface of the virus, not magnified
Type of sample Nasal swab (at Yale) or saliva Nasal swab
Where it is performed In a lab At home kit or in a clinical setting (called point of care testing)
Speed Typically takes about 24 hours to receive a result, but depends on the lab About 15 minutes
Accuracy Very accurate, considered the “gold standard”. Can detect very small amounts of virus early in infection (and also later in infection even when the person is no longer contagious). Less accurate. Negative results may be false negatives (showing a negative result when infection is actually present) early in disease when the amount of circulating virus is low. Positive tests are highly reliable.
What a positive result tells you Evidence of active viral infection or, late in disease (14-90 days out), evidence of past infection. Evidence of active viral infection. No need to repeat in most cases.
What a negative result tells you No evidence of infection Does not rule out infection Should be repeated
When to use it Preferred for accurate diagnosis and for screening when you do not have symptoms and when the turnaround time is good When a rapid answer is needed in someone with symptoms, immediately prior to an event or gathering to determine infectiousness, or at the end of isolation to confirm ok to return to work/school