December 2010 Cheat Sheet
Bob Gosselin writes, “…the abbreviation PFP
is for platelet-free plasma–PFP
usually requires filtration. Kaolin clotting time requires platelet free plasma for testing. However lupus anticoagulant testing using DRVVT
requires platelet poor plasma, which is defined as being less than 10,000/mcL, and there is ample evidence to suggest that filtration is not recommended for non-KCT testing.”
George answers that he was the process of developing a new quick question on the subject of PPP/PFP to learn what PFP means to our participants. The Quick Question is now posted; look for a summary on January 14.
Carrie was working on a hemostasis project for school and asks, “What if a patient has an abnormal PT and PTT that are not corrected by mixing study?”George answers that the combination of a prolonged PT and PTT that do not correct when mixed with normal control plasma lead to the presumption of the presence of a lupus anticoagulant (LA ), sometimes called a non-specific inhibitor. To confirm, you would follow up with a standard LA profile. A far less common possibility is a specific coagulation factor inhibitor.
George provides a link to a Heartwire summary of 2010 clinical trial reports on dabigatran (Pradaxa, Boehringer-Ingelheim) and rivaroxaban (Xarelto, Bayer and Johnson & Johnson).
A case study sent in by a participant: PTT results pre-surgery were 41.4 sec (reference interval 25-32 sec) with PT at 9.6 sec (9.8-11.4), INR 0.9. Six weeks later, after postponement of surgery, the PTT was 46.0 sec, PT normal. The patient was not on blood thinners. He had an elevated erythrocyte sedimentation rate (ESR), 71 mm/hr and C-reactive protein (CRP) of 45. Should the patient have been tested for coagulation factors and LA when the results first came in? George answers that any time there is an unexplained prolonged PTT the laboratory should follow up with mixing studies, which are designed to detect and presumptively identify a coagulation factor deficiency or LA. The results will indicate whether the patient should be further tested using confirmatory tests for a factor deficiency or LA.
George had a communication through the ASCLS Consumer Forum in which a patient with severe chronic bleeding symptoms had been diagnosed as having both a factor VIII and a factor XIII deficiency. The odds of this combination are 1 in 10 billion; there are no published cases. George suggested the factor XIII deficiency conclusion could be false, based on a false positive urea solubility assay. This post generated an interesting response detailing the problem of factor VIII and factor XIII activity order mix-ups from Herb Crown at SLU.