A comparative study between the Chrono-log 700 and the Sysmex CS-2100i analyzers for assessing ristocetin cofactor activity in patients with von Willebrand disease

Objectives A variety of methods are currently used to measure von Willebrand factor (VWF) activity, but still the VWF ristocetin cofactor (VWF:RCo) assay using the manual aggregometry technique is the reference method, even having high inter-laboratory variability. The automated coagulation analyzers offer several advantages for routine testing. Herein the performance of the automated Sysmex CS2000/2100i analyzer was compared to the manual aggregometer Chrono-log 700 for assessing VWF:Co activity in patients suspected of having von Willebrand disease (VWD). Methods Plasma samples from 136 patients were prospectively collected, and blindly analyzed on both instruments, simultaneously. Linear regression analysis, Bland-Altman test, intra-class correlation coefficient (ICC), and area under receiver-operator characteristic (ROC) curve were used to evaluate the performance of the automated VWF:RCo assay. Results There was a strong positive correlation between the two assays (r=0.86, p<0.0001) with an excellent reliability ICC value of 0.81 (95 % CI: 0.74–0.86). A very good degree of agreement between the two assays was also evidenced with an estimated bias of −0.055 (−0.58 to 0.46). The ROC curve for the automated VWF:RCo assay was 0.86 (95 % CI: 0.78–0.92; p<0.0001). Using a cut-off value of 0.44 UI/mL for VWF:RCo activity, the sensitivity and specificity values were 91.2 %, and 88.2 % for the automated assay. The positive and negative positive values for VWD detection were 72.9 %, and 96.7 %, respectively. Conclusions Collectively, these findings indicate that the automated VWF:RCo assay yields comparable results to the manual aggregometry assay, with very good accuracy and precision to help diagnose patients suspected with VWD.