Mixing Studies

Incubated Mixing Studies

From Ruth Spates: Hi George, our mixing study procedure requires the patient plasma and the pooled plasma to be incubated separately, and then mixed, and the PT or PTT performed. This is in addition to the 1:1 mix being incubated and retested, and the separately incubated patient plasma and NPP to be retested. I don’t […]

Prothrombin Time Mixing Studies

A colleague recently contacted George about prothrombin time mixing studies. Apparently, the College of American Pathologists provided a PT mixing study challenge in a recent survey. George discussed PT mixing studies with Fritsma Factor advisers Larry Brace, PhD and Dave McGlasson who helped list reasons for not doing them: Reasons for not performing a PT […]

Automated Bethesda Titre

From Jasmina, Department of Hematology, Postgraduate Institute of Medical Education and Research, Chandigarh India Hello George. This is regarding running the factor VIII assay for the Bethesda assay on automated analysers. When performing the Bethesda assay on the coagulation analysers like the ACL TOP (IL), we make the doubling dilutions of sample and add them […]

Bleeding Disorders

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.

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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.

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