>>/42002/
> they havent isolated the "virus" so impossible to test for it ivan...

Maybe, but does it change anything?

 >>/42005/

> How they took your sample? Blood or mucus from nose/throat?

That was blood test. Another type of test - PCR - is taken from throat, and detects virus in respiratory tract. It shows if you are contagious, but, as far as I know, has very large error rate. I decided to do only blood test, because it is too late for PCR for me (just my opinion). Even that antibody test may be flawed. Or they could just replace my blood sample with other in accident, or something like this - and you can't check it. Maybe doing multiple tests in different labs is a way, but I personally don't really care: I've had the symptoms, they are gone, whatever.

> Are immunoglobulins "one fits them all" type of reaction?

I don't know much about biology, but looks like igM is common, or at least very similar for many diseases, and igG is specific to single virus. So, igG is produced after some time, and igM are first ones, but less specific. Having only igM is not enough to detect anything except "looks like you are ill". Having igG says that you had that virus in past. Or it is error in testing, I guess some tests may mismatch antibodies, depending on disease and type of antibody.

> An acquaintance was ill last year, very ill, some upper respiratory disease, had severe immunreaction to that, they got scared it's maybe covid, they called ambulance. The ambulance did the test and found no covid present.

Quick test (from throat I suppose) detects covid by some third factor, and there are plenty of errors. It also may not detect infection, even if it exists, because it stops to be located in respiratory tract and goes lower (lungs etc). Infection also may be suppressed by antibodies and test may fail because there are too small amount of virus etc.

Doctors need to differentiate by multiple tests, and also by symptomatic. But in most cases, especially before covid, they just see respiratory symptom and say "it's flu or common cold", because testing is relatively long task. Now with coronavirus they often just say "oh, it's covid", even without tests. Considering that treatment for most cases is the same (i.e. do nothing, sit and wait until you are ok or you need to hospitalize), there is a reason why they do this.