Coagulation laboratory tests

Factor XIII assay

Topic Completed: 1 June 2012

Minor changes: 22 September 2020

Copyright: 2002-2022,, Inc.

PubMed Search: Factor XIII assay [title]

Jeremy C. Parsons, M.D.
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Table of Contents
Definition / general
Cite this page: Parsons JC. Factor XIII assay. website. Accessed January 17th, 2022.
Definition / general
  • Indications:
    • Patients with familial bleeding disorder but normal PT and PTT and normal von Willebrand panel
    • Factor XIII deficiency causes delayed bleeding after clot formation due to deficient crosslinking of the fibrin clot

  • Screening assay:
    • Evaluates clot stability in 5M urea
    • Add calcium to patient plasma to make it clot, incubate for 30 minutes at 37C, then place clot in 5M urea for 24 hours at room temperature
    • Normal patients have stable cots, but patients with factor XIII deficiency of 1 - 2% of normal have clots that dissolve in urea
    • Screening assay does not detect heterozygotes
    • 2% acetic acid can also be used as a clot stability screening reagent, but will only detect patients down to 4% deficiency

  • Quantitative assay:
    • Reference range is 70 - 140% of normal
    • Detects values of 50% of normal (heterozygous deficiencies)
    • Expensive and not readily available, factor XIII is activated by thrombin, attaches glycine ethyl ester to a peptide substrate, releasing ammonia detected by photometer
    • High serum ammonia levels falsely decrease the result
    • Newborns may have lower levels than adults
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