2010 Cheat Sheet
An article in the April, 2010 Archives of Internal Medicine identifies the sulfonamide antibiotic cotrimoxazole (Bactrim® and several generics) as conferring a 3.84 odds ratio of upper GI bleeding when co-prescribed with warfarin in patients > ; 66 years. Likewise ciprofloxacin (Ciprol®) co-therapy generated an odds ratio of 1.94, also significant. Co-therapy with amoxicillin, ampicillin, nitrofurantoin or norfloxacin did not significantly raise patient bleeding risk. April 15
Prof. Michele Brown at UAB works with an athletic graduate student who is researching thrombosis in athletes and is looking for publications or anecdotes. George asked for responses from participants who may have some insight or experience. April 16.
Our April, 2010 Quick Question was “Do you collect a discard tube prior to collecting a tube for coagulation testing?” Answers revealed that at least half of us are still doing this. Citing several sources, George states this is unnecessary for routine or special coagulation testing. We can save resources, time, and reduce complexity by eliminating the discard tube. April 20.
Jojie Acosta asks, “After a lab inspection we are required to perform normal whole blood controls each day of testing for our PFA-100. Any suggestions on how to address the required daily QC? Normal donors are hard to find.” George comments the assessor may have been working from a missed or obsolete communication. The package insert for the PFA-100 specifies “wet QC” on new lots only. Dr. Emanuel Favaloro provided the comment that the current CLSI standard recommends but does not require fresh whole blood QC, and that it is inappropriate for the assessor to require this. His preference is to run whole blood QC when the PFA-100 has generated borderline results. A comment from Joe Lamb also supports George and Dr. Favaloro’s positions. May 13
“How do you test for heparin-induced thrombocytopenia (HIT )?” The majority use platelet count plus immunoassay or platelet count plus heparin-induced platelet aggregation. George claims platelet aggregometry is insensitive and likely to miss a significant number of HIT antibodies. The washed platelet suspension aggregometry assay may be more sensitive, though it is technically demanding. Serotonin release is the reference method, but is available from relatively few reference labs, owing to the radioactive isotope. Our current best laboratory/clinical approach is Dr. Warkentin’s “4T” system: Thrombocytopenia (acute); Timing of platelet count fall; Thrombosis or other sequelae and oTher causes for thrombocytopenia. May 13
At the Midwest meeting, Dr Ravi Sarode asked whether every prolonged PTT should be followed with a mixing study. He mentioned first that the PT and PTT were never meant to assess bleeding risk in a non-bleeding patient, although they are routinely misused as admission screens. This was confirmed by data presented later by Dr. Steve Kitchen. Dr. Sarode made the point that the clinical situation may indicate the need to bypass mixing studies and move right into patient treatment. For instance, he presented a case of a PTT of 38 seconds (reference interval 25-35) that corrects to 33 seconds on immediate mixing. Surgery was delayed a week while the laboratory tracked down a transient lupus anticoagulant. Dr. Dorothy Adcock-Funk commented later that there is little to be gained by performing mixing studies on a specimen with a PTT just a few seconds beyond normal. Dr. Sarode emphasized that mixing study techniques are not standardized from lab to lab, use no controls, use no consistent definition for normal pooled plasma and place insufficient emphasis on platelet free plasma. This topic is picked up in a June 3 thread begun by Herb Crown at St. Louis University, May 21
Most transfusion services adopt a policy recommending Novo Nordisk’s recombinant activated factor VIIa (rFVIIa, NovoSeven) in acute hemorrhage when conventional therapy; RBCs, frozen plasma, platelet concentrate, and cryoprecipitate fail to stop bleeding. NovoSeven is FDA-cleared for prophylaxis or therapy in hemophilia A or B patients with inhibitors or people with congenital factor VII deficiency. Several studies have implied that NovoSeven may trigger arterial or venous thrombosis when used off-label in high-risk patients such as those with previous thrombotic disorders. George asks for your institution’s policy regarding the use of NovoSeven, how successful is it, and have you personally witnessed clinical “rescues?” This topic is picked up in a June 1 thread, “New NovoSeven?” May 21
“Dchrist” asks, “What is the clinical rationale for offering both a qualitative and quantitative D-dimer assay? George speculates the laboratory director retains the qualitative assay for a quick turn-around to help diagnose disseminated intravascular coagulation (DIC ), in which D-dimer levels become markedly elevated. The quantitative assay, which is also speedy and could be used for both applications, is primarily used to rule out venous thromboembolism in symptomatic patients who have a low pre-assay clinical score for thrombosis. May 22.
“Mirnaibarra” in El Paso asks, “Do you recommend the 4:1 mix to be used routinely? Also, what is the most common and preferred way of interpreting mixing studies correction; percent correction, a percent of PNP
or the Rosner Index?
George answers that most labs use the 1:1 mix of patient plasma and NP for initial mixing studies, occasionally using a 3:1 or 4:1 mix when a thrombotic picture suggests LA but the 1:1 mix corrects. Dr. Larry Brace also advocates for the 1:1 mix on the grounds that a lupus anticoagulant-sensitive PTT reagent is at least as likely to detect lupus anticoagulant as is a 4:1 mix.
George posted a Quick Question in June polling our participants on their criteria for mixing study correction. The majority of people use correction to within 5 seconds of the normal control plasma. George advocates for correction within 10%, using the Rosner index, whereas Dr. Dorothy Adcock of Esoterix Coagulation requires correction to within the upper limit of the normal range.
Steve Duff of Precision BioLogic alerts us to a new recall of unfractionated heparin posted by the US FDA on October 27, 2010. The supplier, Scientific Protein Laboratories, in testing retained crude heparin lots revealed traces of oversulfated chondroitin sulfate. This is the same problem that created a public health risk in 2008.