Discard volumes necessary for clinically useful coagulation studies from heparinized Hickman catheters.

PURPOSE/OBJECTIVES: Determine the blood volume that must be wasted to obtain a clinically useful prothrombin time (PT), activated partial thromboplastin time (APTT), and fibrinogen concentration for blood drawn from a heparinized (2.5 ml of 100 units/ml), double-lumen venous catheter.

DESIGN

Prospective, nonrandomized study comparing test results obtained from blood samples drawn through the catheters with those obtained via peripheral venipuncture. Patients acted as their own control.

SETTING

Inpatient and outpatient units of a cancer research center located in a mid-Atlantic city in the United States.

SAMPLE

Twenty double-lumen 10 Fr. Hickman catheters (Bard Access Systems, Salt Lake City, UT) were studied in 20 adult patients with cancer who had no history of coagulation disorders.

METHODS

Samples were collected from the red lumen of 20 heparinized, double-lumen Hickman catheters after 5, 10, 15, 20, and 25 ml of blood first were discarded. PTs, APTTs, and fibrinogen concentrations were measured on each sample. The results were compared with those derived from a simultaneously obtained peripheral blood sample.

MAIN RESEARCH VARIABLES

PT, APTT, and fibrinogen values of blood samples after 5, 10, 15, 20, and 25 ml discards and PT, APTT, and fibrinogen of peripheral blood samples.

FINDINGS

The coagulation results using peripheral blood were always within the normal range except for one slightly elevated APTT. After 25 ml of discard, all of the PTs and fibrinogen concentrations and 95% of the APTTs of catheter blood were within the normal range and therefore clinically useful.

CONCLUSIONS

Clinically useful PTs, APTTs, and fibrinogen concentrations often can be derived with catheter-drawn blood when the objective is to confirm normal coagulation. However, because it is very difficult to obtain heparin-free samples through heparinized, double-lumen Hickman catheters, peripheral blood should be drawn for coagulation testing when a totally heparin-free sample is needed to make a critical clinical decision.

IMPLICATIONS FOR NURSING PRACTICE

These findings provide important information for practice when nurses have to decide whether to draw coagulation tests through a heparinized catheter. Further research is needed with larger samples in varied populations (e.g., pediatrics) to study catheters made of different materials and of different calibers.