The aim of this study was to evaluate the analytical performance of a curved capillary configurations on a U-tube structure used in a tabletop fully automated blood viscometer. Precision was assessed using normal and abnormal quality control materials measured repeatedly over 20 days across shear rates of 1–1000 s⁻1. Correlation between straight and curved capillary configurations was evaluated. Sample stability was also assessed at shear rates of 1 s⁻1 and 300 s⁻1 over three consecutive days. The curved capillary system demonstrated robust precision, with total coefficients of variation decreasing with increasing shear rate. Strong correlations were observed between straight and curved capillary measurements across all shear rates. Passing– Bablok regression showed slopes close to unity and intercepts near zero, while Bland–Altman analysis revealed minimal bias without shear-dependent trends. Whole blood viscosity remained stable over three days at both low and high shear rates (all p > 0.98). The curved capillary–based U-tube configuration provides analytically equivalent and stable whole blood viscosity measurements compared with conventional straight capillary systems, supporting its suitability for fully automated blood viscometer.

This study evaluates the analytical performance of a newly developed miniaturized disposable U-tube for an automated blood viscometer and compares it to conventional viscometers. Whole blood viscosity (WBV), essential for circulatory function, exhibits non-Newtonian behavior, posing challenges for measurement at low shear rates. The blood viscometer, based on a scanning capillary tube method, used disposable U-tubes to measure viscosities across a shear rate range of 1s⁻¹ to 1,000s⁻¹. Precision evaluation showed stable coefficients of variation (CV) across different viscosity levels. Repeatability assessment indicated consistent CV values, demonstrating the reliability of the device. The agreement with the LV-III Brookfield viscometer and MCR 92 Rheometer was analyzed using Bland-Altman plots, which revealed minor systematic biases and consistent differences across the measurement range. Correlation analysis using Passing-Bablok regression showed high correlation coefficients (R > 0.96) with regression slopes close to 1. The newly developed miniaturized disposable U-tube exhibits excellent precision, reliable repeatability, and high correlation with established methods, enhancing laboratory productivity and offering potential for clinical applications. Further studies with human blood samples are recommended to confirm its clinical applicability.