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Ristocetin Cofactor Activity

Item Value
Clinical Questions Does my patient have von Willebrand disease? If so, which type?
Approval req'd? No. If testing needed outside of defined testing schedule then approval is required.
Available Stat? No, Contact hematology x3-1747 for special testing needs.
Test code RCOF
Test group vWD
Performed by Parnassus Hematology
In House Availability Run on day shift every other Monday
Method Platelet agglutination
Collection Instructions Check the expiration date on the label of the blue top vacutainer before drawing the patient.

Avoid collecting when patient may be lipemic as this may result in sample rejection.
Container type Blue top filled to full extent of vacuum
Amount to Collect 2.7 mL blood
Sample type Citrated plasma
Preferred volume 1 mL plasma
Min. Volume 0.5 mL plasma
UCSF Rejection Criteria Samples collected in outdated blue top vacutainer. Markedly lipemic samples may be rejected.
Processing notes If this test is ordered together with Factor VIII Activity and Von Willebrand Factor Antigen on the same sample, enter VWP to request all three tests.

Take sample asap to Hematology for processing. Separate and freeze plasma at -20C within 1 hour.
Units %
Normal range 42-191%
Synonyms vW Factor; ; von Willebrand factor activity; VWF activity
Stability Room temperature 4 hours, frozen at -20C 2 weeks. frozen at -80C 6 months.
Turn around times 1-14 days
Additional information Von Willebrand Factor is necessary for platelet adhesion to injured endothelium.

Ristocetin Cofactor is useful in assessing binding of von Willebrand Factor to platelet factor GP1b. When combined with other tests, results are useful in diagnosis of von Willebrand Disease and in categorizing types of von Willebrand Disease.

According to National Heart Lung and Blood Institute von Willebrand Disease Clinical Practice guidelines (http://www.nhlbi.nih.gov/guidelines/vwd/index.htm), a ratio of Ristocetin Cofactor/von Willebrand Factor Antigen of <0.5-0.7 may indicate the presence of a qualitative abnormality in von Willebrand Factor (i.e. Type 2 von Willebrand Disease), provided that Ristocetin Cofactor activity and/or von Willebrand Factor Antigen are below normal. Ristocetin Cofactor/von Willebrand Factor Antigen ratios in an internal UCSF study (December 2008, 39 normal blood donors with normal Ristocetin Cofactor activity and normal von Willebrand Factor Antigen) were all >0.5.

If unusual findings are noted a pathologist review and interpretation may be performed and separately billed for
CPT coding 85245
LOINC code 6014-5
Last Updated 4/1/2014 11:34:49 AM
Entry Number 830
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