Which of these blood tests produces a 50% error rate?!?
I was tested negative once and asked my doc if I could be tested again and she refused stating the test is never wrong. I know there are different types of blood tests out there.
Dragonslayer is referring to the *technique* by which the test is performed.
It used to be always done by the ELISA method (go google it if you want more info). It did have a high false NEGATIVE rate and rarely a false POSITIVE. This is more likely in smaller pathology lab - where the volume (or lack thereof) of that specific test performed was low - so the staff were therefore less experienced at doing it and accurately deciphering the result.
50% of the TESTS DONE were NOT inaccurate - but 50% of those where a negative result was obtained went on to be HLA B27 +ve on re-testing.
Nowadays, most larger labs will do a test for HLA B27 protein via a method known as FLOW CYTOMETRY - this has a very high accuracy rate and will therefore yield a far more reliable result.
Be aware that FC is a sophisticated (and VERY EXPENSIVE!) way of testing for this, so some low budget labs are still likely to be doing the ELISA method.