May 2010 Cheat Sheet
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.