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

Alternate sample:
Collect lithium heparin or lavender EDTA, centrifuge and transfer 1 mL plasma to a screw top plastic vial within 1 hour of collection, indicate sample type on tube and send.

Patient preparation:
Dietary supplements containing biotin may interfere in assays and may skew results to be either falsely high or falsely low. For patients receiving the recommended daily doses of biotin, draw samples at least 8 hours following the last biotin supplementation. For patients on mega-doses of biotin supplements, draw samples at least 72 hours following the last biotin supplementation.