81643-9

LOINC code 81643-9 identifies "von Willebrand factor (vWf) ristocetin cofactor/von Willebrand factor (vWf) Ag [Ratio] in Platelet poor plasma". This term represents a ratio of two results that are expressed as percentages of normal: the von Willebrand factor.ristocetin cofactor activity and the von Willebrand factor antigen concentration, both of which are reported as actual/Normal. The von Willebrand factor (vWF) ristocetin cofactor activity to antigen ratio can help distinguish different types of von Willebrand disease (VWD). VWD types 1 and 3 are usually associated with a quantitative decrease in vWF, which would affect both the vWF ristocetin cofactor activity as well as vWF antigen concentration, while type 2 is associated with a functional defect in VWF, which would affect the activity but not the amount of antigen present. Therefore, patients with type 2 VWD are likely to have a lower vWF ristocetin cofactor activity to antigen ratio (less than 0.6-0.7) compared to patients with types 1 or 3 VWD.

This code measures von Willebrand factor.ristocetin cofactor activity/von Willebrand factor Ag in PPP. It belongs to the COAG class in the LOINC classification.

LOINC (Logical Observation Identifiers Names and Codes) is a universal standard for identifying laboratory and clinical observations. It is maintained by the Regenstrief Institute and used worldwide for health data exchange.