Geometry-Dependent Variability in Rotational Rheometry of Whole Blood: Implications for Flow Curve Measurement and Protocol Standardization

Hemorheology has clear physiological relevance and potential diagnostic value, emphasizing the need for reliable blood rheological measurements. Rotational rheometry is widely used for the characterization of blood flow behavior, yet the influence of measuring geometry on rheological parameters remains insufficiently investigated and standardized. This study evaluated geometry-dependent variability in whole blood rheometry by comparing a double-gap coaxial cylinder (CC27 DG) with two cone–plate geometries differing in size and cone angle (C50 1° and C35 2°). Blood samples from five healthy volunteers were analyzed using an identical shear protocol from 0 to 100 s−1, and flow curves were fitted using the Power law model. All geometries consistently demonstrated non-Newtonian, shear-thinning behavior. Significant overall geometry effects were observed for the consistency index K (p = 0.022) and Power law goodness-of-fit r (p = 0.015), whereas no significant overall effect was detected for n (p = 0.247). While no pairwise comparison reached statistical significance after Holm adjustment, CC27 DG showed the lowest mean K, the highest mean r, and the smoothest flow curves, and C50 1° produced smooth curves with a reduced sample volume requirement. These findings support explicit reporting of measuring geometry and its consideration in the standardization of hemorheological protocols.