Comparison of PT, aPTT, and Factor VII Values Obtained by Concurrent Sample Collection by Direct Venipuncture and Peripheral Venous Catheters

STUDY OBJECTIVE: To compare prothrombin time (PT), activated partial thromboplastin time (aPTT), and factor VII values in concurrent blood samples obtained by direct venipuncture and from a peripheral venous catheter. DESIGN: Concurrent samples obtained from catheters and by direct venipuncture were studied. In a separate crossover bioequivalence assessment of DNA-derived factor VIIa (rFVIIa) from two different batches, sample results of each technique were compared. SETTING: University hospital clinical research unit. PATIENTS: Six patients with hemophilia A under nonbleeding conditions. INTERVENTIONS: The patients received a single dose of rFVIIa 70 micrograms/kg administered by intravenous push over 2 minutes. Concurrent blood samples were collected at 2, 3, 4, 6, 8, 10, and 12 hours after rFVIIa administration. Catheter blood samples were drawn from a three-way stopcock attached to an 18-gauge peripheral venous catheter in the patient's forearm and connected to an intravenous solution of 5% dextrose with half normal saline maintained at a rate of 30 ml/hour. Venipuncture samples were drawn from the opposite arm. MEASUREMENTS AND MAIN RESULTS: The PT and aPTT values were determined by using a BBL Fibrometer (PT) and a Coagamate X-2 with automated aPTT reagent. Blood samples were analyzed for factor VII concentration using the Novo Clot assay. The mean venipuncture-obtained PT (8.9 +/- 1.0 sec) and aPTT (48.7 +/- 13.6 sec) values were numerically equivalent to mean catheter-derived PT (9.0 +/- 1.0 sec) and aPTT (48.3 +/- 12.5 sec) results, as were mean venipuncture and catheter-obtained FVII:C values. CONCLUSIONS: The PT and aPTT values determined after venipuncture and through the peripheral catheter were not statistically different (p > 0.05) when compared by paired or unpaired analysis. Similarly, values of FVII:C measured after venipuncture were statistically equivalent to those after sampling through the peripheral catheter. All six patients preferred the catheter method of blood collection over venipuncture.