Mixing Study with Shortened Incubated PTT

Here is a paraphrase of a recent question: “What accounts for a shortened post-incubation PTT compared to the immediate mix result?”

Example:

• Patient PTT: 50 s
• Commercial PNP PTT: 30 s
• Immediate mix result PTT: 40 s
• 2-h Incubated result PTT: 37 s
  

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Frequent expert contributor Dave McGlasson suggests the patient’s plasma should be checked to ensure it is platelet-poor, as platelets secrete several procoagulants. Do you have any suggestions besides Mr. McGlasson? If so, please answer below.