They send you a requisition form that you then take to the lab (in my case, labcorp) when you get your blood drawn.
Labcorp is not very reliable I guess, according to Dr. Crisler. He told me he only accepts only some of the values from those assays.
From what I understand, Dr. John's on the LEF science board now, so LEF's choice of lab may soon change, I imagine.