2010 Cheat Sheet
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.