A child with hemophilia needs an extraction. Which laboratory test is most relevant?

Correct answer: A. Partial thromboplastin time (PTT/aPTT)

• A. CORRECT. Hemophilia A (factor VIII deficiency) and hemophilia B (factor IX deficiency) are disorders of the INTRINSIC coagulation pathway, which is assessed by the PARTIAL THROMBOPLASTIN TIME. The aPTT is PROLONGED in hemophilia while PT, bleeding time and platelet count are all NORMAL — a pattern that by itself points to the intrinsic pathway. Specific factor assay levels then determine severity and the required replacement dose.
• B. Platelet count is normal in hemophilia. It is the relevant test in thrombocytopenia and ITP.
• C. Bleeding time assesses PLATELET function and vessel integrity. It is normal in hemophilia, where primary haemostasis is intact — which is why these patients form a clot initially and then rebleed hours later as the unstable clot breaks down.
• D. PT assesses the EXTRINSIC pathway (factor VII) and is used to monitor warfarin. It is normal in hemophilia.

Note: Extraction management is coordinated with haematology: factor replacement or DDAVP for mild hemophilia A, plus local measures — antifibrinolytics (tranexamic acid), oxidised cellulose, sutures — and strict avoidance of NSAIDs and aspirin.