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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)
Laboratory
- 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
Additional References
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