Contact system

Author: Jeremy Parsons, M.D. (see Authors page)

Revised: 29 February 2016, last major update June 2012

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Contact system [title] coagulation
Cite this page: Contact system. website. Accessed October 24th, 2016.
Definition / General
  • Consists of coagulation factors unknown in the 1950s
  • Includes factor XII (Hageman factor), prekallikrein (PK; Fletcher factor), high molecular weight kininogen (Williams, Flaujeac or Fitzgerald factor)
    • Some authors include factor XI
  • Made in the liver
  • Decreased activity is associated with liver disease, hepatic immaturity in newborns, antiphospholipid syndrome, Asian descent (for factor XII)
  • Homozygous deficiencies are rare, autosomal recessive
    • Cause very long PTT but no bleeding disorders and no definite association with hypercoagulability
  • Contact pathway may play a large role in inflammation, as patients with factor XI deficiency often have repeated infections
  • Recommended to not measure their activity in routine evaluation of patients with arterial or venous thromboembolism or acute coronary syndromes (Arch Pathol Lab Med 2002;126:1382)
  • Homozygous deficiencies cause prolonged PTT
  • Heterozygous deficiencies have near normal PTT
  • The test for a particular contact factor is based on the ability of the patient's plasma to correct a prolonged PTT in plasma that is deficient in the factor being tested
  • Even though the PTT may be decreased by deficiencies of contact factors, this does not necessarily correlate with increased bleeding risk