Evaluation of the Analytical Performance of von Willebrand Factor Antigen and Activity Tests on the Cobas t511 Coagulation Analyser

Scientific Research Question: New methods for coagulation tests require careful assessment before routine diagnostic use. We evaluated the analytical performance of the Siemens von Willebrand Factor (vWF) antigen and activity assays on the Roche Cobas t511 coagulation analyser by using the Cobas Development Channel (CDC).

Methodology: The Siemens vWF antigen (vWF Ag) and activity (INNOVANCE® VWF Ac) assays were adapted to the Cobas t511 analyser and their analytical performance and method comparisons with relevant commercially available assays were performed according to Clinical Laboratory Standards Institute guidelines using residual anonymized samples.

Findings: Trueness was evaluated by normal and pathological Siemens controls and values were well within the recommended acceptable ranges. Within run precision provided a CV of 0.4% in the normal and 0.5% in the pathological sample pool and day to day precisions were 0.8% and 0.6% respectively for vWF antigen measurements and similar results were obtained for the vWF activity values. The limit of detection was 0.7% for vWF antigen and 4% for vWF activity. The limit of quantitation for both assays were 5% and a single calibration provided vWF results in the range 5-160%. The Deming regression analyses carried out on >120 samples showed good agreement between vWF antigen assay on the Cobas and CS2500 systems (Pearson's r = 0.996) and similar results were obtained with vWF activity (Pearson's r = 0.998). On Bland-Altman plots a systemic deviation could be observed in the lower ranges (below 60% in case of antigen and 40% in case of of activity) where higher values were obtained by the Cobas t511 when compared to the Sysmex CS2500 analyser by using the same reagents. The differences in the lower concentration range may be explained by the difference in calibration procedures.

Conclusion: The CDC is an outstanding possibility to apply 3^rd party reagenst ono the Cobas coagulation analyser. Based on the excellent analytical performance and good agreement with relevant comparator method, the method is useful for routine diagnostic use in core laboratories.