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

Abstract

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 μg/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.