Coagulation
Coagulation laboratory tests
Factor assays
Author: Jeremy C. Parsons, M.D.
Last author update: 1 June 2012
Last staff update: 16 September 2020
Copyright: 2002-2023, PathologyOutlines.com, Inc.
PubMed Search: Factor assays [title]
Cite this page: Parsons JC. Factor assays. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/coagulationfactorassays.html. Accessed November 29th, 2023.
Definition / general
- PT (factors II, V, VII, X) or PTT (factors V, VIII, IX, XI, XII) based reactions, performed by mixing patient plasma with plasma that is deficient in the factor being measured
- The rate limiting reactant is the deficient factor which must be supplied by the patient
- PT or PTT is compared to standard curve, to determine amount of factor present in patients plasma
- Used to determine the etiology of a prolonged PT or PTT
- Factor levels are expressed as a percentage of normal plasma concentration, or units per mL of normal plasma
- Reference range is often 60 - 140% (should be determined based on the laboratorys patient population)
- Perform at multiple dilutions to rule out an inhibitor - at higher dilutions, inhibitor interference should decrease due to dilution of the inhibitor (this gives a nonlinear curve)
- Can also use chromogenic assays to quantitate
- Levels at birth of factors other than factor VIII are 10 - 100% of adult levels, but reach adult levels at 6 months
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