Substantial Differences in Serum Concentrations of Psychoactive Drugs Measured in Samples Stored for 2 Days or More on Standard Serum Tubes Versus Serum Tubes Containing Gel Separators.

Background: Drugs may potentially adsorb to blood collection tubes containing gel separators in the preanalytical phase of therapeutic drug monitoring. The aim of this study was to compare measured concentrations of 28 psychoactive drugs and 13 metabolites in spiked serum samples stored on standard (plain) tubes versus barrier gel tubes during a 2-6-day period at room temperature.

Methods: Drug-free ("blank") serum samples spiked with mixes of antidepressants, antipsychotics, or mood stabilizers (valproic acid and lamotrigine), including relevant metabolites, were transferred to tubes with and without gel, that is, BD Vacutainer SST II Advance gel tubes and BD Vacutainer Glass Serum Tubes (Becton-Dickinson Company, Plymouth, United Kingdom).