Optimization of the Mechanism for Measuring Ristocetin Cofactor Activity ( VWF:RCo ) with the Fully Automated Blood Coagulation Analyzer Sysmex® CS-2000i

• Optimization of the Mechanism for Measuring Ristocetin Cofactor Activity ( VWF:RCo ) with the Fully Automated Blood Coagulation Analyzer Sysmex® CS-2000i

AUTHOR(S)

Nobuo ARAI, Kae MUKAIDE, Toru SUGIYAMA and Kunihiro FUNAKOSHI

Scientific Affairs, Sysmex Corporation

SUMMARY

To make it capable of VWF : RCo measurements, we provided a built-in mixing function in the CS-2000i , comprising a reaction cuvette in which a magnetic stirrer bar is inserted. The shape ( diameter and length ) of the stirrer bar and the stirring speed have major impact on data in this measurement. We conducted various investigations for optimizing the assay conditions to obtain good quality data. After comprehensive evaluation including reproducibility and the slope of the calibration curve, we set the stirrer bar diameter at 1.2 mm and length at 3.8 mm and stirring speed at 900 rpm as the assay conditions. Assay results obtained with two levels of control plasma showed good within-run reproducibility, the CV being 4.4% for normal plasma and 3.3% for pathological plasma. When the sample dilution was changed before measurement in the very low and very high activity ranges, dilution linearity was shown in the 5 – 330% VWF : RCo activity range. The detection limit determined with low VWF : RCo activity samples was found to be 5% activity. The results obtained with the CS-2000i  were correlated with those of the manual method. The two were especially close in the low activity range.

We believe that the CS-2000i , capable of measuring VWF : Ag, FVIII : C and VWF : RCo, can provide useful information for VWD diagnosis.

KEY WORDS

Fully Automated Blood Coagulation Analyzer CS-2000i , VWF, VWF : RCo