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.

Abstract
1. Introduction
2. Materials and Methods
    2.1 Precision evaluation of a curved capillarysystem
    2.2 Method correlation between straight capillaryand curved capillary configurations
    2.3 Sample stability evaluation using a curvedcapillary configuration
3. Results
    3.1 Precision performance of a curved capillarysystem
    3.2 Correlation between straight capillary andcurved capillary configurations
    3.3 Sample stability evaluation
4. Discussion
5. Conclusion
Declaration of Interests
Acknowledgement
References

• Dong Hwan Lee(Department of Mechanical Design Engineering, College of Engineering, Jeonbuk National University) | 이동환 Corresponding author