What is a practical method to screen for factor XIII deficiency?

• A. Clot stability testing (e.g., urea clot dissolution).
• B. Prothrombin time.
• C. aPTT.
• D. Factor XIII activity assay.

Answer: (D)

Factor XIII deficiency affects clot stabilization rather than formation, so assays that measure the enzyme’s activity are the most direct way to screen for it. A Factor XIII activity assay quantifies how well the enzyme cross-links fibrin, providing a specific, functional readout of FXIII status. Routine tests like PT or aPTT look at clotting time formation and are usually normal in FXIII deficiency, so they’re poor screening tools for this problem. Clot stability tests such as urea clot dissolution can indicate a problem with stabilization, but they are less precise and more variable, making them less reliable as a primary screening method. Therefore, directly assessing Factor XIII activity offers the most straightforward and accurate screen for deficiency.