Creatinine Transfer between Red Cells and Plasma: A Comparison between Normal and Uremic Subjects

The rates of efflux and influx between plasma and red cells of 14C-creatinine in freshly heparinized blood taken from normal subjects and from both dialyzed and non-dialyzed uremic patients have been examined in vitro. Influx and efflux experiments were done simultaneously on blood immediately following collection. Experiments were conducted under physiological conditions (pH 7.4, T = 37°C). Samples were analyzed by liquid scintillation spectroscopy and data were reduced by computer using a first-order model of mass transfer. There were no differences between creatinine partition coefficients in normal and uremic blood (red blood cell/plasma equilibrium distribution coefficient = 0.72 ± 0.03; n = 21). There were also no significant differences between the specific rate constants (Ks) for either influx or efflux (t = 1.7; n = 21), or between dialyzed and non-dialyzed uremics (t = 0.23; n=10). However, there was a highly significant difference (p < 0.001) between normal and uremic rate constants. For normals, the equilibrium half-life for creatinine transfer was 15 min (Ks = 0.026 ± 0.002 min-1; n = 21) and, for uremics, 26 min (Ks = 0.015 ± 0.001 min1; n=10). The significance of these results is the implication that normal mass transfer rates between cells and extracellular fluid may not apply in the uremic state.