Effects of contaminants in blood-collection devices on measurements of therapeutic drugs.

Substances in evacuated blood-collection devices produce gas-chromatographic peaks with retention times similar to those of drugs. All tubes tested except the serum separator tubes contained tris(2-butoxyethyl) phosphate, as determined by mass spectrometry. In addition, the partition coefficient during the solvent-extraction step increased for some drugs by as much as 40%, while for other drugs it decreased by as much as 30%, depending on the drug and the collection tube. The Becton Dickinson serum separator tube also contains several other compounds identified by mass spectrometry to be dibasic esters used in the preparation of the polyester gel. The Corning serum separator tube and the Venoject serum tube contain still other impurities. The Becton Dickinson royal-blue-stoppered tube contained the least amount of impurities of the tubes tested. CVs of 25 commonly measured drugs in plasma pools increased from 5% for samples collected in glass tubes to greater than 20% for samples collected in evacuated blood-collection tubes. Clearly, accuracy and precision of measurements of therapeutic drugs can be seriously compromised if an inappropriate blood-collection device is used.