Platelet Function Testing

Ristocetin Cofactor

Laura Lum, Seattle Children’s Hospital, asks, What is the ristocetin cofactor assay for, how is it performed, and can it be done on an STA Compact? Hi, Laura, the ristocetin cofactor assay is a test for von Willebrand factor (VWF) activity. Low VWF is the cause of von Willebrand disease (VWD). The assay began as platelet aggregometry […]

Bleeding Disorders

New Ristocetin Lot and Storage Requirements

We’ve had two questions about Ristocetin since our 11.9.11 Problems with Ristocetin question from Kerri Klemm. Kerri’s question prompted me to contact Kathy Jacobs at Chrono-log Corp, a major distributor of ristocetin in the US and around the world. Here is a follow-up message from Kathy: Hello George, Nice to hear from you and a very happy New Year to you and your family. As […]

Bleeding Disorders

Adapting Ristocetin Cofactor Assay Reagent

Has anyone been able to adapt a third-party reagent for ristocetin onto a Stago STAR-E or Compact? If so, would you be willing to share your experience with the product, validation procedure, etc? Please feel free to reply off-line if you so desire, and thank you in advance, Dorothy Zdanowicz, Chemistry/Coagulation Supervisor Englewood Hospital & […]

Bleeding Disorders

Acceptable Interval for VWF:RCo

George, Our lab participates in both CAP CGE and NASCOLA ECAT proficiency challenges. One of those assays, von Willebrand factor ristocetin cofactor (VWF:RCo) activity by the agglutination method, is difficult to judge in terms of performance. When looking at results, what is acceptable for criteria? I usually look for ±2 SD for other tests. Sometimes […]

Bleeding Disorders

Any Problems with Ristocetin?

From Kerri Klemm: Has anyone had problems recently with ristocetin-induced platelet aggregation? We have used this reagent for years and just recently had problems. We run the ristocetin at 1.5 mg, which should react and does and 0.75 mg, which shouldn’t react but does. This is with our normal controls who we have used before. Until […]

Platelet Function Testing

Quick Question Summary: PFT Blood Collection

Here’s a summary of our October, 2011 Quick Question, “What specimen do you require for platelet function testing?” The answers: a. Two-syringe technique using a butterfly set: 1 (2%) b. Two-syringe technique using a Luer-slip needle: 1 (2%) c. 3.2% citrate (blue-closure) tubes by standard collection: 37 (74%) d. 3.2% citrate (blue-closure) tubes using a […]

Platelet Function Testing

Case: A 5-YO with Ecchymoses: Your Opinion?

Posted October 4, 2011, and still looking for an answer: Here is a recent case from the ASCLS Consumer Forum. A 5-YO female experiences chronic ecchymoses with minimal trauma, CBC results are normal, platelet count 343,000/uL with normal morphology, bleeding time is 4 minutes. PT, PTT, fibrinogen, and thrombin time are normal. Using light transmittance aggregometry, there […]

Platelet Function Testing

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George Fritsma is a medical laboratory scientist, educator, and author. George is a member of the International Society on Thrombosis and Hemostasis, the International Society for Laboratory Hematology, and the American Society for Clinical Laboratory Science.

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