In the majority of US states you can order lactate dehydrogenase 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 DirectLabs because they have the cheapest price I know of ($29), and I've been happy with their service. You can also compare the other 6 lactate dehydrogenase test providers I've found.
Take a look at my state-specific issues page if you're in AZ, MD, NJ, NY or RI.
I won't pretend to understand when you'd want to test for particular isoenzymes (LD-1 through LD-5), but here's the providers I found for that: