[Determination of the factor VIII ristocetin cofactor (Willebrand factor) using a semi-quantitative slide test....

The assay of factor VIII, co-factor of Ristocetin (VIIIR:Co) is a relatively delicate procedure which is presently reserved to specialized laboratories. It requires the use of an aggregometer and a long and difficult preparation of human platelets. In parallel with this classical method, we have used a new, rapid, semi-quantitative slide test whose advantages are: simple technique and rapid answer (2 minutes), small volume of plasma required for the test (50 microliters) and the possibility of using citrated or heparinized plasma taken form a venous or capillary blood sample. Using this test, we have assayed factor VIII co-factor of ristocetin: in 31 hospitalized adults patients with no previous history of bleeding and no disturbance of haemostasis and in 18 patients with Willebrand's factor deficiency in comparison with the standard technique using aggregometry (Allain's method); - in 28 normal neonates, in comparison with the VIIIR:Ag factor assay (Laurell's technique), only because of the small sample volume available; - in 17 patients with various disease associated with an abnormality of the VIII complex in comparison with the assay of VIIIR:Ag and VIIIC. The results obtained in the normal adults show a satisfactory correlation between the two methods. The mean level of factor VIII:Co is 100 +/- 10 per cent (M +/- SD) with the semi-quantitative slide test and 109 +/- 20 per cent (M +/- SD) with the method taken as the reference. The correlation is also satisfactory for patients with a deficit of Willebrand's factor. The test performed on the neonates gives a mean value of 101 +/- 37 per cent (M +/- SD) with good correlation between the factor VIIIR:Ag and the factor VIIIR:Co.