Order PTH (parathyroid hormone) blood testing online
In the majority of US states you can order PTH testing online and have the blood drawn at a local blood draw center (see my general overview of the process).
I'd suggest ordering from Walk-In Lab because they have the cheapest price I know of ($38), and I've been happy with their service. You can also compare the other 6 PTH test providers I've found.
Take a look at my state-specific issues page if you're in AZ, MD, NJ, NY or RI.
Understanding the results
Chris Masterjohn, a man roughly 17x smarter than me, has a helpful podcast episode discussing PTH.
The American Association for Clinical Chemistry has helpful pages for understanding the test and answering common questions.
If you're interested in self-testing as I am, check out my Facebook or Twitter account where I post interesting self-testing news and get a little too excited about blood test sales.