Viscometer validation studies for routine and experimental hemorheological measurements.

BACKGROUND: Viscosity measurement is challenging due to the internal properties of blood and the artifacts deriving from the various viscometer systems. OBJECTIVE: We aimed to determine the pitfalls of a cone-plate viscometer (Brookfield DV-III Ultra LV) before starting measurements and compare it to our capillary type model (Hemorex Hevimet 40). Effects of sample storage and thermal calibration were assessed as well. METHODS AND RESULTS: Intra-observer variability was studied by 10 replicate measurements of 7 blood samples, mean coefficients of variation were less than 5%. Instruments were compared by measuring 26 blood samples, an average difference of 7% in WBV and 10% in PV was observed. 9 blood samples were stored at 4 degrees C, 22 degrees C and 37 degrees C up to 48 hours to study the effect of storage on viscosity values. WBV at 50 and 100 s(-1) became significantly lower after 3 hours at 37 degrees C (p < 0.05). WBV at higher shear rates and PV remained constant at all temperatures. To evaluate the possibility of measuring one sample at different temperatures, 8 blood samples were measured at 40 degrees C with the device calibrated both at 20 degrees C and 40 degrees C; no significant difference was observed. CONCLUSIONS: Thorough validation studies are required before starting experimental and routine viscosity measurements.