I want to talk about the testing for coronavirus and all the difficulties with the new testing options. I was contacted 3 times last week. Once by a patient, once by a friend, and twice by lab companies trying to get me to buy a bunch of the new point of care (POC) tests. The patient was actually approached directly at HIS company, and they were trying to sell directly to him there. I presume to be able to test any employee and decide whether they need to go home or be quarantined or something. In my opinion they are just trying to make some money off these tests. I recommend against this.
Let’s talk about why. Short answer is this: we dont really know the utility of the IG tests yet. The problem is (epidemiology nerd stuff coming) the positive predictive value is horrendous. That means what likelihood can I predict a positive result. When we are testing for covid with the strictest criteria we are only getting 1-2% positive in this state. Maybe even up to 3 or 3.5%. So i PREDICT that 99% of the time these ab tests will be negative. So positive predictive value is terrible.
So when getting a positive test, I’m not expecting that. So then do i believe it? Or is it a false positive? Would I tell that person they have covid and need to quarantine for 2 weeks? Also at least with other corona viruses, the false positive rate on these types of tests is relatively high. Then if i get a negative test however, it’s not worth a darn. I expected a negative, so it doesnt change anything. I cant tell that person they are good they can go to work. The IgM (which is the early immunoglobulin in a disease) doesnt turn positive for 4-5 days usually. So if i get a negative on day 2 or 3 are they good to go? Or do I need to retest them to confirm?
Lastly what does a positive IgG (this is the longer immunoglobulin that suggests previous exposure and immunity) mean? Is that person immune? How long are they immune (most corona viruses are 1-2 years)? Can they get it again? These are all questions we dont even know the answer to.
I think these tests can be used appropriately with a direct contact with a physician who interprets within the clinical assessment. I wouldnt recommend laypersons just doing a swab and making an assessment off of the results.
I also dont think docs or clinics should just be testing everyone that walks in the door. I would recommend steering clear of those. They either dont know how these tests are supposed to be used (a bad sign) or are just trying to make money off of the hysteria (also a bad sign).