Covid-19 Testing Accuracy & 4 Kinds of Tests

 In Health Blog

Four kinds of Covid-19 testing:

  1. PCR. It is when your nose is swabbed with a giant Q-tip (clinics and cars)
    • Test for active infection and is currently the most accurate.
    • Almost no false positives
    • Around 20% false negatives.
    • Best in early stages. If the virus has migrated out of the nose into your Lungs it probably will not detect it. 
    • Results take 1 to 5 days, or 10-14 days if backed up. 
    • In-clinic may be more accurate than drive-through.  
    • If asymptomatic or pre-symptomatic (no symptoms) it has a 70% false negative rate. 
  2. Rapid (point of care) test (e.g. Abbott ID Now)
    • Results in 20-40 minutes. 
    • High false negative (30-40%)
  3. Antigen test
    • Rapid test
    • Results in 5-10 minutes.
    • Very high false negative rate, think White House Rose Garden, around 50%. 
    • No False positives.
  4. Antibody test
    • Results takes days to weeks.
    • Tells you if you have previous exposure.
    • It usually takes 2 weeks to show up after exposure
    • Requires a blood sample. 

Relevant Take Aways:

  • All tests have very low false positive. That means if you test positive on a test,  you probably have it and should assume so. If you test negative, you could easily have it, especially if you have symptoms. 
  • A negative test does not mean you are safe and cannot infect others.  If you have had exposure you need to assume to are contagious!
  • Virus cycle is on an average of a 10 day cycle. The first half pre-symptomatic (up to 70% false negative testing for PCR), second half, symptomatic (more easily detected). It takes a couple of days after infection to show a positive.
  • If you test positive (in test 1-3 above), you are potentially contagious, as you have active virus occurring. You must quarantine.

Reference: Podcast with Dale Harrison, expert in molecular diagnostics.

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