New: CDC says don’t use antibody tests yet: “It cannot be assumed that individuals w/ truly +antibody test are protected. Serologic testing should not be used to determine immune status in individuals until durability & duration of immunity established." https://www.cnn.com/2020/05/26/health/antibody-tests-cdc-coronavirus-wrong/index.html

2) "In most of country, including areas that have been heavily impacted, prevalence of SARS-CoV-2 antibody is expected to be low, ranging from less than 5%-25%, so that testing at this point might result in relatively more false positive results & fewer false-negative results”

3) “The higher the sensitivity, the fewer false negatives a test will give. The higher the specificity, the fewer false positives. Across populations, tests give more accurate results if the disease being tested for is common in the population.”

4) “If an infection has only affected a small percentage of people being tested, even a very small margin of error in a test will be magnified.

If just 5% of the population being tested has the virus, a test with more than 90% accuracy can still miss half the cases.”

5) The problem with with low POSITIVE PREDICTIVE VALUE when prevalence low. I’ve even covered this long ago in January - see math below to understand how PPV affected: https://twitter.com/drericding/status/1223157702270050304?s=21 https://twitter.com/drericding/status/1223157702270050304