This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Best assay for deficiency of von Willebamd factor is: 
Select and explain. 
A. Bleeding time, B. BT + APTT, C. BT + APTT + vWF-ristocetin factor assay, D. PT
C: BT + APTT + vWF-ristocetin factor assay
Answer: C: BT + APTT + vWF-ristocetin factor assay 
Explanation: Answer is C (BT + APTT + vWF-ristocetin factor assay) Estimation of BT, APTT and VWF-Ristocetin factor assay would provide the maximal information to aid a diagnosis of VWF disease (amongst the options provided)