Mixing Studies

Nijmegen-Bethesda Assay Method

Sarah Payne and Kerri Klemm request information on how to perform the CDC modification of the Nijmegen-Bethesda Assay for coagulation factor inhibitors. Thank both of you for your request, which provides George the opportunity for self-promotion. Please tap or click Coagulation Factor Inhibitors and the Nijmegen Bethesda Assay, a recording of my June 2 digital […]

Bleeding Disorders

Coagulation Assay Protocol

Hello Mr. Fritsma, First of all thank you for taking the time to put together such an informative resource. I have found it very helpful in carryout coagulation tests as part of my master’s thesis in Biomedical Science. I based some of my assays on the procedure found on page https://fritsmafactor.com/post/teaching-mixing-studies and I would like to […]

More on Mixing Studies

Here is additional information on mixing studies provided by John Olson, MD, who is a “seasoned” CAP inspector. Dr. Olson cautions that he is not speaking for CAP, but providing his expert opinion. He cites CAP HEM.37991, Mixing Studies Procedure: When plasma-mixing studies are performed, an appropriate pooled plasma is utilized. NOTE: It is not […]

Mixing Study Correction Limits

Dr. Tony Tang asks, In a mixing study, how many seconds difference between the APTT of the test plasma+normal plasma (NP) incubated after mixing together, and the APTT of the test plasma and NP incubated separately before mixing, can suggest a positive result for factor VIII inhibitor? Are there any references? Thank you! Hello, Dr. […]

Mixing Study Dilution

From Mahnaz Sairi, Hello, George. We use pooled normal control plasma (PNP) from George King and lately found out that mixing buffer with PNP and using that as a control is confusing our physicians. Because they are asking why the control results are increasing? I really do not know why we are diluting the plasma […]

DRVVT Divisor

Maria Cordova, Mayo Labs, asks, How would calculate your DRVVT screen divisor? Hello, Maria, and thank you. You’ve opened a provocative topic and inspired me to relive fun we had with our provocative September 25, 2015 post on this subject, “Don’t Normalize the DRVVT.” This attracted perhaps the most attention of any 2015 topic. I’ll […]

Lupus Anticoagulant

Mixing Studies and the Rosner Index

Here is another excellent question from Sheila Minor: We use the Rosner index for both interpretation of a PT or PTT mixing study and for LA testing, in which we follow up the DRVVT confirm and ratio with a 50:50 DRVVT mix to resolve discrepancies. Most references state that a Rosner index value of 15 or […]

Lupus Anticoagulant

What Result Triggers a PTT Mix? QQ Summary

Here is the summary of our October-November, 2015 Quick Question, “What PTT value initiates a PTT mixing study in your laboratory?” The question drew 157 responses. Any PTT result longer than the upper limit of the reference interval: 25% PTT result longer than the upper limit of the reference interval pending physician consult: 18% PTT […]

What Result Triggers a PTT Mix?

From Heather DeVries, Indiana University Health, “I answered the current Quick Question saying that we use another decision limit for doing a PTT mixing study. We require that the PTT be >3.0 seconds prolonged beyond the upper limit of our reference range, which is is 38.0 seconds. Thank you, Heather, there seems to be great […]

PTT Mixing Studies

From Alan Neal, Pathlab, New Zealand: We don’t reflex mixing studies unless clinically directed as they need a responsible clinician to discuss with haematologists. I strongly believe mixing studies can be misleading and numerous studies have identified lupus-like anticoagulants (LLACs, LACs) that correct with APTT mix study; approx. 40% abnormal APTTs do not have an […]

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George Fritsma is a medical laboratory scientist, educator, and author. George holds faculty appointments with Rutgers University and Michigan State University, and is a member of the International Society on Thrombosis and Hemostasis, American Association of Clinical Chemists, and American Society for Clinical Laboratory Science.

Cheat Sheets from George

Quick Question