Collect SST, after 30 minutes of clotting, promptly centrifuge and send 1.0 mL serum.

Alternate sample: Red top or green lithium heparin

Patient preparation:
Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample. This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R).