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5 M Urea for Factor XIII

From Pam Owens: Hi George, good to see you at THSNA! (Thrombosis and Hemostasis Summit of North America). I am hearing more about how ineffective the 5M urea test is for factor XIII screening and am thinking we just need to stop doing the assay in our lab. I’ll need to convince our lab director. Are there any articles or published studies out there? I’m not having any luck looking on line.


Hi, Pam, and thank you for your question. The 5 M urea solubility assay is a “time-honored” means for measuring factor XIII but it is not particularly sensitive. I know that many lab directors have replaced it with a quantitative assay, but I’ve seen no validation studies or head-to-head comparisons. However, I’ve been able to turn up two  comprehensive review articles that describe the old and new assays. Here they are:

Iran J Ped Hematol Oncol 2013 FXIII

Factor XIII Def Hemophilia 2008

Comments (2)
Factor Assays
Alan Neal
May 2, 2014 9:02am

Older publication, but it highlights issues with screening t
Older publication, but it highlights issues with screening techniques: Problems relating to the laboratory diagnosis of factor XIII deficiency: a UK NEQAS study. Jennings I1, Kitchen S, Woods TA, Preston FE; UK NEQAS. J Thromb Haemost 2003;1:2603-8.

Apr 29, 2014 7:48am

Also, according to recent statement of SSC subcommittee of t
Also, according to recent statement of SSC subcommittee of the ISTH, this assay is not recommended as screening:
“Traditionally, the solubility of fibrin clot in concentrated urea, acetic acid or monochloroacetic acid solution was used to screen for FXIII deficiency. This is a qualitative method that detects only very severe FXIII deficiency. The method is not standardized; its sensitivity depends on the fibrinogen level, the clotting reagent (thrombin and/or Ca2+), and the solubilizing agent and its concentration. Depending on these variables, the detection limit of the clot solubility assay varies between <0.5% and 5% FXIII activity. The high number of undiagnosed or late-diagnosed FXIII deficiencies is partly attributable to the practice of using this test as the diagnostic criterion of FXIII deficiency. The use of this method as the screening test for FXIII deficiency is not recommended."
Diagnosis and classification of factor XIII deficiencies.

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