The effect of hemodialysis ultrafiltration on changes in whole blood viscosity

Increased whole blood viscosity (WBV) can be injurious to the vascular endothelium and increase the risk of atherothrombotic events. This study examined the effect of hemodialysis ultrafiltration (UF) on WBV, with a focus on high vs. low-volume UF patients. In stable hemodialysis patients, blood was drawn for hematocrit (Hct) and WBV at the start, midpoint, and at the end of dialysis. For analysis, patients were divided into high UF (≥2700 mL) or low UF (<2700 mL) groups. A total of 59 patients completed the study. Mean Hct increased during dialysis in both groups. The intradialytic increase in Hct was significantly greater in the high vs. the low UF group (3.2% vs. 1.28%, P = 0.01), with a significantly higher end-dialysis Hct in the high UF group (40.5% vs. 38%, P = 0.02). At the end of dialysis, both high shear rate WBV (P < 0.01) and low shear rate WBV (P < 0.01) were significantly higher in the high UF compared with the low UF group. There was an approximately two-fold greater increase in high shear rate (P < 0.01) and low shear rate (P = 0.01) WBV during dialysis in high vs. low UF groups. The increase in high shear rate WBV during dialysis was significantly correlated with an increase in Hct (R2 = 0.63, P < 0.01). We found that hemodialysis UF causes a surge in WBV. The surge was of greater magnitude in high than in low UF patients.