April 2010 Cheat Sheet
Kim Kinney at
Clarian asked about screening for suspected prekallikrein (PK
, Fletcher factor) when the PTT
is prolonged. George suggests you can incubate the plasma with PTT
reagent for 10–20 minutes and repeat the PTT. If the PTT
result corrects to normal, it probably means PK
deficiency caused the initial prolongation. This works when the PTT
reagent uses kaolin or Celite, but not ellagic acid as its activator. George speculates that the kaolin or Celite activates factor XII upon prolonged incubation and bypasses the need for PK.
Kim also noticed that people with high molecular weight kininogen (HMWK , Fitzgerald factor) deficiency seem to have PK deficiency. This discussion was left open. April 7
Subscriber Dkaguni asks, “Historical ranges are often used to determine the range for coagulation assays. Are there general guidelines as to how large these ranges can be?” George assumes the question addresses internal assay precision, expressed as coefficient of variation (CV%). Per Dr. John Olson, there is no historical range for an acceptable CV%. Some may be as small as 4%, other assays are clinically effective at > ;10%. The key issue, as recommended by Dr. Olson, is that the laboratory perform and record local (in-house) precision studies to confirm manufacturer’s claims. Methods for in-house precision studies are presented in audio modules 3 and 4. For preparation of reference intervals (normal ranges), the standard approach is to assay aliquots from a well-defined cohort of normal subjects and compute the mean and standard deviation. The typical reference interval is ± 2 SDs. Methods for computing reference intervals are provided in audio modules 5 and 6. April 13
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.