They use a swab, like a large Q-tip in the cheek area. Then they mail that to the lab.
It will tell them what liver enzymes the patient has or don't have. Different medicines need different liver enzymes to metabolize the medication. My daughter was missing an enzyme for some medications, and had twice as many of a different enzyme, so processed that type of medication too quickly.
It also provided a list of medications, divided in o three columns. 1. Recommended medications. 2. Use with caution. 3. Use with extra caution.
Ksm