Determining optimal waste volume from an intravenous catheter.

Waste is blood drawn from an intravenous (IV) catheter to remove saline or heparin before obtaining a blood sample. This study examines the minimum waste volume resulting in an undiluted sample. A repeated-measures design was used. Investigators placed an IV catheter in 60 healthy adults and obtained samples at baseline and following waste volumes ranging from 0.5 to 3 mL. A random effects mixed model was used to determine the stabilizing point, which was 1 mL of waste. Knowing that only 1 mL of waste is needed will prevent clinicians from obtaining extra waste and discarding blood needlessly.