Hi Dow,
Yep, the HLA B27 is done with a simple blood draw but I think it is a bit more expensive than your average ESR check, or at least it used to be. Up here, (a few decades ago now) when I had it done, they had to send it away to one specific lab in our province that was capable of doing it. That may have changed by now, however.
With a history of SI joint pain but, for instance, no sign of inflammation or loss in range of motion, I think some docs would think differently than others about jumping ahead with this test. It is not used for exploring what a diagnosis may be but more for confirming or supporting a diagnosis... if that makes sense. This is because 8% of normal healthy people are B27 positive. So yes, it is an easy test but will not tell a doctor much of anything unless in combination with other findings that seems suspicious enough to warrant further investigation.
I am not sure that ongoing SI joint pain, in the absence of any history or trauma would be enough reason or not, just on it's own? I personally doubt it but it may depend on the doc. In combination with a female who has been previously dx'd with Fibro, I would want it checked.
Checking ESR and/or CRP should come first, imo. Ah, but what do I know!
