A message from Kim Kinney at Clarian:
Hi George, I am giving a case study presentation and one of the studies is about a woman who had a homozygous HMWK (Fitzgerald factor) deficiency. While we were working her up we read in a reference about the Fletcher factor (PK) screening test where you incubate patient plasma with PTT reagent that contains either kaolin or silica as the activator. If after a 10-minute vs the usual 3- or 5-minute activation the time corrects, it could be a PK deficiency. Do you know why this happens?
Also, I read that moderately low PK levels are found in most homozygous HK deficient patients. Do you know why that is other then they bind together? Thanks, Kim
Hi, Kim. Love your questions, they gave me another two hours in the books! There are several articles from the 70s and 80s documenting the 10-minute incubation with kaolin or Celite to detect PK deficiency. This does not work with PTT reagents that use ellagic acid as the activator. However, none of the articles even speculate on the mechanism.
I’ve had the notion that the prolonged incubation activates XII and HMWK, subsequently activating XI while bypassing PK, but have no proof. The prolonged incubation does not correct the PTT prolongation associated with XII or HMWK deficiency. See Hattersley PG, Hayse D. The effect of increased contact activation time on the activated partial thromboplastin time. Am J Clin Pathol 1976; 66: 479.
I’ve not seen an association of PK deficiency with HK deficiency, and couldn’t find it in my two favorite references, Colman or Kitchens. Please send me your reference, as I am curious. Meanwhile, maybe one of our participants has the answer. Geo.