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Background
The Ristocetin Cofactor (RCoF) test is used to evaluate the function of von Willebrand factor (vWF). This factor is a key protein in hemostasis. It is a multimeric glycoprotein with a molecular weight of 1000 to 20000 kDa. It contains monomers in megakaryocytes and endothelial cells. It released from the platelets and endothelium after the activation. The half-life of vWF is about 12 hours.
VWF gives support to the adhesion of platelet to impaired sub-endothelium to form a hemostatic plug. It prevents the proteolytic degradation in the plasma. vWF: RCo test assess the functional activity of protein, aggregation of platelet to vWF in presence of ristocetin is same to the hemostatically active form of vWF.
To reduce the poor sensitivity of this test at the lowest activity of vWF: RCo, which is less than about 20 to 30%, a new protocol of vWF: RCo test was identified and validated. Tests to measure the vWF activity were developed, and it utilizes microparticles, which are covered with recombinant platelet receptor glycoprotein Ib. It binds to vWF and make the combination of vWF: GPIb in the absence or presence of ristocetin. This can replace the standard vWF: RCo test in future.
Indications/Applications
The Ristocetin Cofactor test is suggested in the following cases:
To diagnose vWD (von Willebrand Disease)
To differentiate the subtypes of vWD
Type 1 vWD: Mild quantitative deficiency of vWF
Type 2 vWD: Any qualitative defect in vWF
Type 3 vWD: Severe quantitative defect of vWF
To differentiate vWD to hemophilia A
To monitor the treatment of vWD
To assess the function of vWF in acquired vWD
Reference Range
Normal range of ristocetin cofactors as per the age group:
Newborn (Below 6 months): 50 to 200% (IU/dL)
Children (1 to 10 years): 40 to 130% (blood group O), 50 to 180 % (except blood group O)
Adults: 50 to 150% (blood group O), 60 to 180 % (except blood group O)
Interpretation
Inherited deficiency of vWF:
Type 1: Moderately reduced level of RCoF activity with reduced levels of vWF antigen. vWF: RCo to vWF: Ag ratio is about greater than 0.7.
Type 2: RCoF activity is more reduced than the vWF antigen level. vWF: RCo to vWF: Ag ratio is about less than 0.7/ vWF: Ag level is mostly normal in vWD types 2B and 2A.
Type 3: Severe reduced or absent activity of RCoF and vWF: Ag. The ratio of vWF: RCoF and vWF: Ag is less than 5%.
Acquired deficiency of vWF:
Autoimmune inhibition or clearance which can cause diseases like:
Lymphoproliferative diseases like leukemia, lymphoma
Systemic lupus erythematosus (SLE) or other autoimmune diseases
Monoclonal gammopathies like Waldenstrom macroglobulinemia, multiple myeloma
Cancers like carcinoma, Ewing sarcoma, Wilms tumor
Causes of deficiency of vWF because of elevated shear-induced proteolysis:
Ventricular septal defect, which looks like small sized pinhole
Primary pulmonary hypertension
Severe aortic stenosis
Extracorporeal life support
Other causes are like:
Drug-induced like valproic acid, hydroxyethyl starch
Hypothyroidism
Myeloproliferative diseases like thrombocythemia, polycythemia
Glycogen storage disease
Angiodysplasia
Elevated activity of vWF: RCoF and vWF: Ag are seen in acute phase reaction, which may be linked to the following conditions:
Stress
Inflammation
Extensive exercise
Cancer
Postoperative period
Obesity
Diabetes
pregnancy
Atherothrombosis
Atherosclerosis
Collection And Panels
Sample type: Citrated plasma
Sample collection tube: Blue top tube which contains 3.2 % sodium citrate
Centrifugation: centrifuge about 2000 to 2500g sample for 15 minutes to get the platelet-poor plasma
Sample storage: Store the frozen plasma for 6 hours at 18 to 25 ºC. Samples are stable for 1 month at -20 ºC.
Panels:
Complete blood count (CBC) test like RBC count test, platelet count test, peripheral smear test
Coagulation tests like partial thromboplastin time, prothrombin time
vWF tests like vWF antigen test, vWF factor VIII binding test, vWF collagen binding test, vWF genotyping test
Factor VIII activity tests
Both our subscription plans include Free CME/CPD AMA PRA Category 1 credits.
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