Plasma hemoglobin measurement techniques for the in vitro evaluation of blood damage caused by medical devices.

A sensitive measure of the in vitro blood damage potential of a medical device is the rate at which hemoglobin is released into the plasma from red blood cells flowing through the device. Presently there is no one widely accepted method for measuring the plasma hemoglobin concentration. Nine currently used assays, classified as either direct optical or added chemical techniques, were evaluated for accuracy, reproducibility, sensitivity, interference effects, and ease of use by adding hemoglobin (1-200 mg/dl) to saline, lipid, and bilirubin solutions and to normal cow plasma. Most of the assays displayed good linearity, accuracy, and reproducibility down to 1 mg/dl when interferents were absent. However, representative of the effects caused by interferents, the endogenous hemoglobin concentration of a typical cow plasma sample measured by the 9 techniques ranged from -2 to 39 mg/dl. Although used by fewer organizations, some of the direct optical spectrophotometric methods (e.g., the Cripps and Harboe baseline correction methods) are safer, easier, and more precise and accurate than the chemical addition methods used to measure plasma hemoglobin concentration from in vitro blood damage testing of medical devices.