Comparing the results of coagulation tests on blood drawn by venipuncture and through heparinized tunneled venous access devices in pediatric patients with cancer.

PURPOSE/OBJECTIVES To compare the accuracy of three coagulation tests (prothrombin time [PT], activated partial thromboplastin time [aPTT], and fibrinogen [FBG]) performed on blood samples collected through heparinized tunneled venous access devices (TVADs) with those from venipuncture. DESIGN Descriptive comparative with patients serving as their own controls. SETTING Pediatric comprehensive care setting for children and adolescents experiencing catastrophic diseases. SAMPLE 53 patients who had TVADs, had not received asparaginase during the previous 14 days, and had coagulation studies ordered. Patients ranged in age from 2-20 years (mean = 9.2 years, SD = 5). The most common diagnoses were neuroblastoma and acute myelocytic leukemia. METHODS Blood was collected through TVADs within seconds of collection of the venipuncture sample. The first 3 ml of blood from a TVAD was discarded; the research nurse then drew three sequential samples of 3 ml each. Laboratory personnel were blinded to the source of all four samples until all analyses had been completed. MAIN RESEARCH VARIABLES PT, aPTT, and FBG. FINDINGS For all patients, results of PT, aPTT, and FBG tests on each of the three blood samples obtained through the TVAD differed significantly from results of the same tests on blood obtained by venipuncture. CONCLUSIONS These findings indicate that neither a 6 ml, 9 ml, nor 12 ml discard from a heparinized TVAD is sufficient to yield clinically trustworthy PT, aPTT, or FBG values. IMPLICATIONS FOR NURSING Nurses who have been persuaded by patients or parents to withdraw blood samples for coagulation indicators from a TVAD rather than from a venipuncture should have access to this research-based information that the three indicators, particularly aPTT, differ significantly from each other as to make it unreliable and potentially unsafe to sample blood from a TVAD to assess coagulation.