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Specimen Collection Manual and Test Catalog

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RISTOCETIN COFACTOR ASSAY

Geisinger Epic Procedure Code:  LAB3014    Geisinger Epic ID:  7126

SPECIMEN COLLECTION
Specimen type: 

Platelet-poor plasma


Preferred collection container: 
Alternate collection container: 
3.5 mL blue-top (3.2% sodium citrate) tube
Specimen required: 

1 mL


Special notes: 
  • If the patient’s hematocrit (HCT) is >55%, the volume of anticoagulant in the tube must be adjusted. Contact a performing location for sodium citrate adjusted tubes or instruction for how to adjust the sodium citrate.
  • When possible, use fresh venipuncture.
  • Avoid prolong tourniquet time (< 1 minute) and hemolysis during collection as this will alter results.
  • If indwelling catheter or butterfly collection device must be used, draw sample from a non-heparinized lumen or flush the line with 5 mL of saline and discard/use first 5-10 mL of blood for other purposes.
  • Tubes should be >90% filled.
  • Immediately mix gently after collection by inverting the tube end over end 5 to 6 times. Avoid vigorous mixing or additional inversion. Observe for the presence of clots or hemolysis and recollect if observed.


SPECIMEN PROCESSING
Processing instructions: 

Centrifuge as soon as possible (within 60 minutes) at designated speed and time to obtain platelet-poor plasma (< 10,000/uL). Remove plasma and re-spin the plasma for 10 minutes at 3000 rpm and submit platelet free plasma.

For a single NaCit blue top tube collection, create 1 aliquot NaCit and if additional plasma remains, create an additional aliquot NaCit. If multiple tubes collected, create 1 aliquot NaCit for each NaCIt blue top tube collected plus one additional aliquot NaCit. Aliquots should be 1.0-1.9 mL and all plasma-based coagulation tests must be moved to aliquot(s).


Transport temperature: 

Frozen on dry ice


Specimen stability: 

Room temperature (whole blood): 4 hours 
Frozen -20°C: 30 days 
Frozen -70°C: 6 months


Rejection criteria: 

Clotted, hemolyzed, grossly icteric, grossly lipemic, improperly filled tubes, improper anticoagulant ratio (HCT >55% and citrate not adjusted), refrigerated specimens, or stability exceeded.

Note: Specimen suspected of thawing in transport, indicated by slant in aliquot or specimen in lid of tube, will have testing performed, and the comment “interpret results with caution as thawing suspected” added to results.



TEST DETAILS
Reference interval: 

> 40%


CPT code(s):  85245
Note: The billing party has sole responsibility for CPT coding.  Any questions regarding coding should be directed to the payer being billed.
The CPT codes provided by GML are based on AMA guidelines and are for informational purposes only.

Test includes: 

von Willebrand Factor activity


Methodology: 
Aggregation
Synonyms: 

Von Willebrand Factor Activity Assay, RICO, Clotting, VIII, VW, Vonwillebrand, VWF activity


Clinical significance: 

Von Willebrand factor (VWF) is a glycoprotein synthesized in megakaryocytes and endothelial cells that is utilized in primary hemostasis (platelet aggregation) and as a carrier site for the clotting factor VIII. Decreased quantity and/or functionality of VWF leads to mucocutaneous bleeding and menorrhagia. Low VWF levels can be observed in acquired or congenital von Willebrand disease (VWD)

Ristocetin cofactor assay (VWF:RCo) is one type of test used to assess for VWD. It assesses the ability of the patients VWF to agglutinate reagent platelets. It is typically part of a panel of tests (including factor VIII activity and VWF antigen). Abnormalities could be suggestive of a VWD.


Doctoral Director(s): 
Michelle Grant DO
Review Date:  09/03/2026

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