Test Code LAB335 Ristocetin Cofactor, Blood or Plasma
Additional Codes
46860
Reporting Title
Ristocetin Co-factor Assay
Methodology
Platelet Aggregation with Ristocetin
Used to detect abnormalities of von Willebrand factor which is associated with von Willebrand’s syndrome.
Performing Laboratory
OhioHealth Laboratory Services-RMH Core Coagulation
Specimen Requirements
Submit only 1 of the following specimens:
Riverside Inpatient and Riverside Campus draw sites:
Testing must be performed within 4 hours of draw if submitting unprocessed whole blood.
Draw a full, light blue-top (citrate) tube; and send citrated whole blood. Invert several times to mix blood. Forward unprocessed whole blood promptly at ambient temperature only. Do not refrigerate.
Note: 1. This assay requires its own specimen.
2. Indicate whole blood on request form.
3. Label specimen appropriately (whole blood).
Outpatient/Outreach Clients:
Plasma-Frozen
Draw a full, light blue-top (citrate) tube. Spin down, remove plasma, spin plasma again, and place 1 mL of citrated platelet-poor plasma 2 in plastic vials. (Glass vial is not acceptable.) Pour-off vial should be no more than 2/3 full. Send specimen frozen.
Note: 1. This assay requires its own specimen.
2. Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.
3. Indicate plasma on request form.
4. Label specimen appropriately (plasma).
Specimen Transport Temperature
Ambient/Refrigerate NO/Frozen NO-Blood
Frozen/Refrigerate NO/Ambient NO-Plasma
Reference Values
Adults: 50-150%
Results of <40% von Willebrand factor are considered abnormal and suggest von Willebrand’s disease. Values >40% do not rule out the possibility of a variant of von Willebrand’s. Diagnosis of variant forms necessitates a series of clinical and laboratory evaluations including patient and family histories, platelet function assay, factor VIII related antigen, and factor VIII activity level.
Day(s) Test Set Up
Monday through Friday
Test Classification and CPT Coding
85245