A 4-year-old boy has delayed umbilical stump bleeding and recurrent scalp hematomas. PT, aPTT, platelet count and bleeding time are all normal. The clot dissolves within hours in 5M urea. Deficiency of which factor explains this picture?

• A Factor XIII ✓
• B Factor XI
• C Factor VII
• D Factor X

Explanation

Factor XIII cross-links fibrin monomers via epsilon-gamma glutamyl lysine bonds, stabilizing the clot against plasmin. Its deficiency gives normal screening tests because PT and aPTT measure fibrin formation, not stabilization. Delayed bleeding after trauma or cord separation with clot solubility in 5M urea or monochloroacetic acid is diagnostic. Factors VII, X and XI deficiencies would prolong PT or aPTT.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.