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PTT Mix Prolonged Beyond Patient PTT

From “Danagah” (originally posted February 23, 2012):
Hi, George, have you seen the situation when, in the 1:1 immediate mix of a partial thromboplastin time (PTT) mixing study, the PTT is longer than the patient’s initial PTT? The patient does not appear to be on heparin (data to follow):

Patient PTT: 39.0 sec
Normal pool: 30.9 sec
1:1 immediate mix: 41.0 sec

Patient PT: 18.0 sec
Normal pool: 13.8 sec
1:1 immediate mix: 15.1 sec
Your expertise is greatly welcomed! Thank you.

Thank you for your question, and yes, there is an anecdotal phenomenon called “lupus anticoagulant cofactor” that is sometimes associated with a PTT mix that is actually prolonged beyond the prolongation of the patient plasma alone. I’ve found one publication documenting the LA cofactor, McGlasson DL, Higgs J. Presence of a lupus anticoagulant without the usual associated clinical conditions. Clin Lab Sci 1992;5:141–2.  In this article the prolongation was evident when using a kaolin-based PTT reagent but disappeared when using an elagic acid-based reagent. I’ve not heard about this happening in a PT-based mixing study, however, so I’d like to hear from others if they have seen this. Geo.

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