Mixing Studies

LAC Profile: PTT Versus PTT-LA

From “Ari.” Hi George, I stumbled upon your amazing site when researching this question and was wondering if you could shed some light on this. I have a patient who had a DVT. His PCP noted a slightly prolonged aPTT and sent mixing studies. From what I can tell, the aPTT mostly corrected with mix, […]

Lupus Anticoagulant

PTT Mixing Studies

A message from Rose Markarian, Providence Health & Services: What is the purpose of incubating pooled normal plasma (NP) separately and the patient’s plasma separately for 60 minutes? Then after 60 minutes of incubation you mix them together and run to get a PTT and this is labeled as control tube. Please explain! Thank you […]

Rosner Index Case

Hi. I am Krishna. I would like to ask about the interpretation of an APTT (PTT) mixing study that we performed by calculating the Rosner index: Patient sample: 51.4 s Normal plasma (NP): 28.9 s Immediate 1:1 mix: 29.0 s Incubated 2 h, 37°C 1:1 mix: 86.6 s Rosner index formula: (Mix PTT – NP […]

Mixing Studies: 4:1?

From Dr. Deanna Franke, Carolinas HealthCare System: Thank you so much for all the valuable resource information on your website! My question relates to use of variations of mixing studies–specifically the use of dilutions during mixing studies: 1:1 vs 4:1 and saline mix. In what situations is it appropriate to use these variations? Hello, Dr. […]

Quick Question: Mixing Study Results

The stem of our June, 2017 Quick Question was, “In a PTT mixing study, the patient’s initial PTT is 67 s, RI 25–35. The PTT is repeated after mixing 1:1 with NP, and the new result is 63 s, NP 30 s. What do you do next?” This was a quiz question with a correct […]

Nijmegen Bethesda Assay

Dr. Ali Sadeghi-Khomami, Precision BioLogic Inc., provided these in-depth technical questions about the Nijmegen Bethesda Assay (NBA), which we use to quantitate specific factor inhibitors such as anti-factor VIII or anti-factor IX. George forwarded his questions to Connie Miller and Amanda Payne, US Centers for Disease Control and Prevention (CDC) who have been working on […]

Bleeding Disorders

Quick Question: Mixing Study

A comment revealing a weakness in our June, 2017 mixing study quiz from Susan Atkinson ART MLT, Moncton, NB: There is no indication that a thrombin time was performed and normal. This is essential before any investigations are performed so that heparin contamination can be ruled out. This is the usual explanation of an elevated aPTT.

Mixing Study Incubation Time

From Heather DeVries. Hi George! Do you know the reasoning behind using a 2-hour vs 1-hour incubation in mixing studies? We have always used 2 hours, and I wonder if it has to do with the heterogeneity of the antibodies we are trying to pick up. Our pathologist probably has a very good explanation, but […]

Chilling The NBA Reaction Mixture

From Dr. Mirta Arias: Dear George, Thank you for your answer in the blog. I have another question. Dr. Robinson in ISLH argued that it is good to chill the post 2 hour/37°C 37 incubation mixtures of patient + pool normal plasma, and control at 2–8°C for 10 minutes and then measure the factor VIII. In […]

Bleeding Disorders

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

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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