Table 2. Laboratory methods to determine von Willebrand factor levels.

	Measurement	Principle	Method	Advantage	Disadvantage
vWF antigen (vWF:Ag) a	Quantity	Antibody captures protein	ELISA, LIA or flow cytometry	High availability in laboratories	Different cut-off values for different assays Not sensitive for low levels No differential sensitivity to variable molecular weight forms of vWF
vWF propeptide (vWF:pp) a	Quantity	Antibody captures protein	ELISA	Sensitive parameter for vWF release	Different cut-off values for different assays Little commercial availability
vWF ristocetin co-factor (vWF:RCo) a	Activity	Ristocetin induces platelet aggregation through GPIb–vWF interaction	Aggregometry, standard coagulation instruments, LIA or flow cytometry	High availability in laboratories Availability at the bedside with timely results	High variation of coefficients Limited inter-laboratory reproducibility and standardization Poor sensitivity for low vWF levels
vWF collagen binding (vWF:CB)	Activity	Collagen induces vWF binding	ELISA or flow cytometry	Sensitivity to high molecular weight vWF Sensitivity to low vWF levels Little variability	Lack of comparative data
vWF activity	Activity	Recombinant gain of function GPIb binds to vWF	LIA or ELISA	Easy performance and automation High assay accuracy and precision Detection of vWF at low levels	Lack of comparative data

Abbreviations: ELISA, enzyme-linked immunosorbant assay; GPIb, glycoprotein Ib; LIA, latex-particle immunoassay; vWF, von Willebrand factor.

Note: Key points for different assessment of von Willebrand factor.

^aIndicates tests used in stroke studies.