One 3 mL plain red top tube, preferred. EDTA or heparinized plasma are also acceptable.

Separation of serum or plasma from cells within 2 hours is preferred. 1 mL serum at 2-8°C.

Specimen Requirement: A steady state trough (pre-dose) sample is generally accepted as most consistent for therapeutic drug monitoring. Time of last dose should be noted on the requisition.

Use a consistent specimen matrix for serial monitoring of each patient.

Refrigerated: 7 days; Frozen: 4 weeks

Gel separator tubes