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Lab Dept:
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Coagulation
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Test Name:
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RISTOCETIN COFACTOR
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General Information
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Lab Order Codes:
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RISTM
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Synonyms:
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Willebrand Factor Activity; VW Factor Assay
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CPT Codes:
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85245 - Factor VIII vW Factor, Ristocetin cofactor
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Test Includes:
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Ristocetin cofactor resulted as a %.
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Logistics
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Test Indications:
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Aid with the differential diagnosis of hemophilia and type of von Willebrand disease.
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Lab Testing Sections:
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Coagulation (Minneapolis Campus)
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Phone Numbers:
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Minneapolis: 612-813-6280
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St. Paul: 651-220-6550
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Test Availability:
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Twice Weekly (Tuesday and Friday)
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Turnaround Time:
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3 – 5 Days
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Special Instructions:
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See Patient Preparation
Deliver immediately to the laboratory at room temperature.
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Specimen
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Specimen Type:
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Whole blood
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Container:
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Light Blue (Buffered Na Citrate 3.2%) top tube
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Draw Volume:
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2.7 mL blood
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Processed Volume:
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0.9 mL plasma
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Collection:
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A clean venipuncture is essential.
Patient’s with hematocrits levels >55% must have a special tube made to adjust for the hematocrit; contact laboratory for special tube.
Mix thoroughly by gentle inversion.
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Special Processing:
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Lab Staff: All testing will be performed in Minneapolis.
St. Paul Lab: Send whole blood specimens to Mpls for processing via courier. Must be processed within 4 hours of collection. Contact Mpls prior to sending.
Mpls Lab: Spin sample collected in blue top tube for 5 minutes on the Stat Spin centrifuge, remove plasma and transfer to a 4 mL BCS sample cup. Spin plasma again for 5 minutes in the Stat Spin Centrifuge. Transfer plasma to a new BCS sample cup for analysis leaving approximately 200 uL in the bottom of the original cup to discard. Store at frozen (-70 degrees C) temperatures if not run immediately.
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Patient Preparation:
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No Heparin for 2 days prior to testing.
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Sample Rejection:
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Improper tube; clotted specimen; underfilled tube; mislabeled or unlabeled specimens
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Interpretive
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Reference Range:
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Age
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Healthy Preemie
Range (%)
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Full Term Infant Range (%)
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Day 1
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78 – 210%
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86 – 220%
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Day 5
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72 – 219%
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83 – 197%
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Day 30
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66 – 216%
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69 – 187%
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Day 90
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75 – 184%
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84 – 162%
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Day 180
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54 – 158%
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62 – 152%
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Childhood
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Range (%)
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1 – 5 years
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60 – 120%
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6 – 10 years
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44 – 144%
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11 – 16 years
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46 – 153%
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Adult
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50 – 158%
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Critical Values:
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N/A
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Limitations:
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N/A
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Methodology:
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Measurement of agglutination of formalin-fixed platelets by patient’s plasma with ristocetin as compared to agglutination produced by a standard plasma used to prepare a curve.
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References:
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Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis
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Updates:
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5/24/2010: Tubing of patient specimens is no longer prohibited.
12/14/2010: Processing information updated.
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