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Coagulation laboratory tests

Factor assays

Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 20 June 2012, last major update June 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.


● 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 patient’s plasma
● Used to determine the etiology of a prolonged PT or PTT
● Factor levels are expressed as % of normal plasma concentration, or units per mL of normal plasma
● Reference range is often 60-140% (should be determined based on the laboratory’s 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

Additional references

Kolde, Hans-Jurgen. (2004). Haemostasis. Basel, Switzerland: Pentapharm Ltd.

End of Coagulation > Coagulation laboratory tests > Factor assays

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