A novel approach to laboratory assessment of platelet von Willebrand factor

Objective The interaction of platelets with von Willebrand factor (VWF) is essential for primary haemostasis. Concentration and activity of plasma VWF are routine parameters in the assessment of haemostasis disorders. In addition to plasma VWF, platelet VWF, synthesized in megakaryocytes and stored in alpha-granules of circulating platelets, is known to contribute to primary haemostasis and the microenvironment of thrombus formation. The laboratory assessment of platelet VWF however is cumbersome and not widely established as a routine parameter. We here propose a method for laboratory assessment and reporting of platelet VWF potentially useful for laboratory routines in specialised laboratories.

Material and Methods To improve the preparation of platelet VWF we obtained 7.5 ml of EDTA anticoagulated whole blood and added PPACK, apyrase and prostaglandin E1 for platelet inhibition. Platelet separation was conducted with 1 separation and 2 washing steps. The following lysing step with CHAPS as detergent isolated the platelet VWF that was analysed with automated certified test systems. We propose 3 calculation models for a standardised presentation of platelet VWF.

Results Our models allow to describe the concentration of platelet VWF as 1., the proportion of platelet VWF in total VWF activity in whole blood, 2., the amount of platelet VWF in a platelet sample with a defined concentration of 100 platelets/nl, and 3. the concentration of platelet VWF in one platelet. According to our results in healthy individuals, the proportion of platelet VWF activity is estimated to be more than 10 % of total VWF in human plasma under physiological circumstances. The amount of platelet VWF is estimated to be 0.4 IU/ml in a sample with a defined concentration of 100 platelets/nl and to be about 42 IU/ml in one platelet (both expressed as VWF:Ag).

Conclusion We describe a standardized and practical approach for measurement and reporting of platelet VWF concentration and activity. Due to the simplified methodology up to three samples can be reliably processed concurrently, further advantages are small sample volumes, high yields of extracted protein, use of standard certified diagnostic and comprehensible parameters for both clinical and scientific purposes. We conclude that our proposed method may be suitable for routine application in specialized coagulation laboratories.

Publication History

Article published online:
18 June 2021