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Test Name:
Ristocetin Cofactor Assay
- SBMF No:
25250 - Performance Lab Name:
Hem-Coag - Test Mnemonic:
RISTO - ABN:
Not required - CPT Code:
85245 - LOINC Code:
6014-5 - Also Known As:
von Willebrand Factor Activity - Spec Type:
Platelet-poor plasma (PPP) - Spec Container:
Light blue top (3.2% buffered sodium citrate) tube - Pref Vol:
2.0 mL (Two aliquots, 1.0 mL each) - Fasting:
No - Patient Prep:
Collect prior to initiation of anticoagulant therapy - Spec Collect:
- Routine venipuncture
- • NOTE: Traumatic puncture invalidates sample for coagulation studies and necessitates recollection
• Observe proper collection order for coagulation tests; collect tubes for coagulation studies prior to collecting tubes containing clot activators, additives, or anticoagulants
• Fill light blue top tube to stated tube volume
• If coagulation study is only test ordered, collect 1.0 to 2.0 mL blood into tube for discard, then collect light blue top coagulation study tube(s)
• If multiple coagulation studies are requested, submit additional samples for each coagulation test
• Immediately after collection, gently invert tube to mix
- Spec Process:
- Separate plasma from cells immediately
- • Promptly centrifuge 15 minutes
• Carefully transfer plasma portion of sample to separate plastic tube using plastic pipette
• NOTE: Buffy coat layer of sample must be avoided
• Centrifuge transferred plasma sample again to produce platelet-poor plasma (PPP)
• Use second plastic pipette to carefully transfer PPP sample into plastic aliquot tubes
• Immediately freeze PPP samples
- Spec Store Transport:
Frozen - Spec Stability:
4 hours room temperature (20-30°C)
2 weeks frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles - Spec Reject:
Citrate tube underfilled
Sample clotted or hemolyzed
Plasma not frozen within 4 hours of collection - Spec Remarks:
Platelet-poor plasma (PPP) samples obtained by double centrifugation are critical for accurate coagulation studies as platelet contamination may cause spurious results - Methodology:
Spectrophotometry - Use:
Aid in the diagnosis of vonWillebrand Disease and of diseases with changes in the Ristocetin Cofactor activity, such as vascular endothelial lesions, inflammations, and preoperative screening of bleeding tendency - Clinical Significance:
Ristocetin cofactor (vW factor; VIII:vW; vonWillebrand factor) is the property of the Factor VIII protein that is responsible for the agglutination of platelets in the presence of ristocetin. Decreased quantities or abnormalities of the vonWillebrand factor are associated with vonWillebrand syndrome, thus making quantitation of the factor most valuable in the diagnosis and evaluation of this coagulopathy.Levels of vonWillebrand factor are determined by the ability of a test plasma and ristocetin to induce agglutination of a standardized platelet suspension. - Reference Range:
60-160%Interpretation:
A result of less than 60% vonWillebrand factor is considered abnormal and suggestive of vonWillebrand syndrome. However, values over 60% do not rule out the possibility of a variant of vonWillebrand syndrome. Diagnosis of the variant forms of this coagulopathy necessitates a series of clinical and laboratory evaluations including patient and family history, bleeding time, Factor VIII related antigen, and Factor VIII coagulant activity.The Ristocetin Cofactor activity fails to reflect accurately vonWillebrand's Disease in several situations such as pregnancy, infusion of commercial Factor VIII concentrates or administration of 1-deamino[8-d-arginine]-vasopression (DDAVP). In such instances, VIIIR:RCo may be corrected, yet the bleeding time remains prolonged. In addition, VIIIR:RCo levels may be normal in Type II B vonWillebrand's Disease even though the bleeding time is prolonged.
- Critical Low Value:
30% - Critical High Value:
500% - Additional Test Info:
Limitations of the Procedure:
In some cases of Type IIB vonWillebrand’s Disease, normal or borderline Ristocetin Cofactor activities were reported. Treatment of patients with FVIII:C concentrates or DDAVP (1-deamino-[8-D-arginine]-vasopressin) may raise Ristocetin Cofactor activity levels in patient plasma. - Day Run:
Mon-Thu - Time Run:
7:00 am - Time Reported:
5:00 pm - Test Type:
COAGULATION
