Covid-19 Testing Accuracy & 4 Kinds of Tests
Four kinds of Covid-19 testing:
- 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.
- Rapid (point of care) test (e.g. Abbott ID Now)
- Results in 20-40 minutes.
- High false negative (30-40%)
- Antigen test
- Rapid test
- Results in 5-10 minutes.
- Very high false negative rate, think White House Rose Garden, around 50%.
- No False positives.
- 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.