Prekallikrein (PK), also known as Fletcher factor, is a 85,000 Mr serine protease that complexes with HK. PK is the precursor of plasma kallikrein, which is a serine protease that activates kinins. PK is cleaved to produce kallikrein by Factor XII (Hageman factor). [1]
Hereditary deficiencies in PK are very rare resulting in little to no bleeding problems. However, PK deficiency can cause a prolonged APTT, which can be corrected by incubating the patient’s plasma.
Deficiencies in PK can also be required due to some disease states, such as angioedema, infection, DIC, and sickle cell disease.[1]
PK was initially described by Hathaway et. al. in 1965 after encountering a Kentucky family who exhibited strikingly abnormal APTT results, but showed no bleeding symptoms. The family appeared to have a hereditary deficiency in an unknown coagulation factor, dubbed “Fletcher factor” after the family. In 1973 Kirk Wuepper determined that Fletcher factor and prekallikrein were the same.[2]
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