Which tests are performed to screen for pediatric factor XIII (FXIII) deficiency?

Updated: Jun 28, 2021
  • Author: Helge Dirk Hartung, MD; Chief Editor: Cameron K Tebbi, MD  more...
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Results from standard hemostatic screening tests such as activated partial thromboplastin time (aPTT) and international normalized ratio (INR) assessments are normal in factor XIII (FXIII) deficiency.

Assessment of clot stability is the most common screening test for factor XIII deficiency, even though sensitivity and specificity are low.

The patient's plasma is incubated with thrombin with or without calcium for a sufficient period to allow formation of a stable clot; the formed clot is suspended in 5 mol/L urea, 2% acetic acid, or 1% monochloroacetic acid. Thrombin (without calcium) and acetic acid may provide the most sensitive combination.

In the presence of factor XIII, the clot is stable for more than 24 hours; in its absence, the clot dissolves in minutes to hours.

The qualitative test findings are positive in the absence of factor XIII; however, factor XIII levels as low as 1-3% may be sufficient to crosslink the fibrin, stabilizing the clot. Therefore, in patients with milder deficiencies or in patients who have recently received a transfusion, results of the clot stability assay may be normal.

A quantitative assay is required to confirm the diagnosis of factor XIII deficiency.

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