Mixing Studies on Minimally Prolonged PTs and PTTs

I pose this question to see what others are doing in this scenario and what literature there is to support your practice. We commonly get mixing study requests in which the PT or PTT are just minimally out of our normal range, such as 0.1 seconds outside for PT. Is this 0.1 second enough to do the mixing study or is there a buffer such as one second for PT and slightly more for PTTs in which although it is outside the normal range, that a mixing study could be not done? I don’t recall ever seeing one of these minimally prolonged PT/PTT turn out to be an inhibitor on followup. I would appreciate your feedback. Thanks. Bruce King, M.D.

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Using the PTT After Cardiac Catheterization

This question was forwarded by an American Society for Clinical Laboratory Science Consumer Web Forum volunteer: Our hospital currently uses activated clotting time (ACT) results during heart catheterizations to monitor heparin dosage. The ACT is also used as a guide for pulling the sheath. The nurse confirms that the ACT is less than a certain value before removing the sheath. Would it be possible/advisable to use the partial thromboplastin time (PTT) result instead of ACT as a guide to pulling the sheath if the patient has been transferred to a room and the ACT device is not available for testing?

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Please join our sponsor Precision BioLogic Inc at Booth 106 in the Thrombosis and Hemostasis Summit of North America Biennial meeting this week, Thursday, April 10–Saturday, April 12, 2014 at the Chicago Sheraton. While there, please plan to visit our posters, McGlasson DL, Fritsma GA, #53: Do We Need To Normalize the Dilute Russell Viper Venom Time Screen/Confirm Ratio?, Thursday, April 10, 4–5:30; and McGlasson DL, Fritsma GA, Ezzell E, Anderson N: #139: Comparison of Four Dabigatran Assays in an Anticoagulation Clinic Population, Friday, April 11, 5–6:30. We look forward to seeing you there.


Hyperglycemia and Prolonged PTT

From “BJ:” I recently cared for a 60 yr old type 2 diabetic in hyperglycemic hyperosmolar state. Initial serum glucose 960. The partial thromboplastin time (PTT) was initially 78 seconds without clear reason. The international normalized ratio (INR) was 1.4. The prothrombin time (PT) was not initially checked. I felt that the value was likely spurious and I repeated the test a few hours later, with normal result. At that time blood glucose had improved to within the 300s with fluids and insulin. Are you aware of a mechanism whereby severe hyperglycemia can cause the PT/PTT to result artifactually high?
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Specimen Management

From Joanna Carroll: I was recently told that samples should be double spun prior to long term freezing. Except in the case of heparin testing, I cannot find any evidence to support this. Also can you tell me if there are recommendations on how to handle samples for fibrinogen, D-dimer and unfractionated heparin anti-Xa assays? Our fibrinogen package insert only mentions how long the sample is good for at room temperature, and our D-dimer insert only mentions how to handle the sample after freezing. The CLSI document does not cover these tests. Thanks for your help.
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Inpatient Thrombophilia Testing

Another message from colleague and friend Kelly Townsend, Tricore Reference Laboratories, Albuquerque. Hi George, at one of our large teaching hospitals, we are working with the Internal Medicine department to establish “best practices” for ordering thrombophilia testing on inpatients. Has anyone out there successfully implemented guidelines they are willing to share? Any recent references would also be greatly appreciated. Thanks!
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Revalidating Sta-Clot LA

From Rose Markarian, Supervisor Hematology,  Saint John’s Health Center, Santa Monica, CA: Hi George, We perform Stago’s confirmatory hexagonal phase Sta-Clot LA test for lupus inhibitor testing. We validated Stago’s recommended cut off value of ≤ 8.0 seconds several years ago when the test was implemented. Do we have to validate the cut off value with each new lot of reagent? Please advise.
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Platelet Clumping

From Kelly Townsend at Tricore Labs: We have a patient whose platelets clump in every anticoagulant we’ve tried. He has normal prothrombin time, partial thromboplastin time, fibrinogen, and von Willebrand disease panel results, but oozes after even minor procedures. The clinicians want to evaluate platelet function, but we are hesitant because of his platelet clumping. Any suggestions for obtaining accurate platelet function analyzer (PFA-100)  and/or platelet aggregation results in a platelet clumper? We use the Chrono-log Lumiaggregometer (whole blood).

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