Minimum discard volume from arterial catheters to obtain coagulation studies free of heparin effect.

With the use of the canine experimental model, the accuracy and reliability of coagulation test results were compared between arterial samples and samples obtained by venipuncture. The age of the catheter, the concentration of the heparinized flush solution, and the minimum discard volume were evaluated to obtain coagulation study results free of heparin effect. Thirty-seven paired samples of PT, aPTT, and TT were obtained. Analyses revealed no significant difference in test results between new lines and 7-day-old lines, nor between heparin concentrations of 1 unit/ml, 2 units/ml, or 4 units/ml. A minimum discard volume of five times the dead space (measured from catheter tip to sampling proximal stopcock) resulted in accurate and reliable PT, aPTT, and TT test results from the arterial catheters.