Evaluation of evacuated blood-collection tubes: effects of three types of polymeric separators on therapeutic drug-monitoring specimens.

The potential of three types of separator materials found in conventional blood-collection tubes for interference in therapeutic drug measurements was assessed. None of the separators (based on acrylic, silicone, or polyester polymers) had any significant effect on the concentrations of seven drugs (theophylline, digoxin, phenytoin, phenobarbital, gentamicin, ethanol, and cyclosporine) in blood specimens that were processed and analyzed promptly. Storage of specimens for 24 h resulted in an average 2.4% increase in theophylline values in specimens collected in tubes with the acrylic separator (P = 0.024); an average 8.1% decrease in phenytoin in specimens collected in tubes with the polyester-based separator (P < 0.001); and an average 4.2% decrease in phenobarbital in specimens collected in tubes with the polyester-based separator (P = 0.02). All other drug concentrations were not significantly affected. A small decrease in phenytoin (7.9%; P < 0.01) was seen when the specimen volume in 7-mL tubes containing polyester-based separator was reduced to 1.0 mL; all other drug concentrations were unaffected by partial filling of tubes. Paired blood specimens from pediatric patients, when collected in plain tubes and tubes containing acrylic separator, yielded no significant differences for theophylline, digoxin, tobramycin, phenytoin, or phenobarbital concentrations. The three commercially available separators had only small effects on therapeutic drug concentrations, and a newly developed separator based on an acrylic resin was suitably inert.