Blood collection tubes for tricyclic antidepressant drugs: a reevaluation

We tested clinical samples from patients receiving four commonly monitored antidepressant drugs--amitriptyline, nortriptyline, imipramine, and desipramine--to evaluate the reliability of currently available Becton-Dickinson Vacutainer brand vacuum blood collection tubes. Serum tubes (red stopper), heparinized plasma tubes (green stopper), and two types of serum separator tubes (SST) were evaluated. Antidepressant concentrations were measured by reversed-phase high-performance liquid chromatography. Antidepressant levels obtained using fresh serum (red stopper) or plasma (green stopper) yielded equivalent results. Serum collected in red-stopper tubes was stored at 4 degrees C for 4 weeks without detectable loss of antidepressant drugs. Significant concentration decreases for amitriptyline, imipramine, and desipramine were noted when serum was collected in SST tubes to such an extent that SST tubes cannot be used for the procedure. Bias attributed to SST tubes can interfere with the usefulness of clinical results over the entire therapeutic ranges of these drugs.