Hemophilia

A child bleeds into his joints after a minor bump — his platelet count is perfectly normal. The problem isn't the platelets; it's what happens after the initial plug forms.

Hemophilia is an X-linked recessive clotting factor deficiency that disrupts secondary hemostasis — the coagulation cascade — while leaving primary hemostasis (platelet plug formation) intact. Hemophilia A (factor VIII deficiency) accounts for ~80% of cases; Hemophilia B (factor IX deficiency, Christmas disease) accounts for most of the rest. Because it's X-linked, it overwhelmingly affects males, with females as carriers. The hallmark presentation is deep bleeding: hemarthrosis (bleeding into joints, especially knees, elbows, ankles), deep muscle hematomas, and prolonged bleeding after surgery or trauma. Superficial cuts and petechiae are NOT typical — those point to platelet disorders. The key lab finding is a prolonged aPTT with a normal PT, normal platelet count, and normal bleeding time. Severity correlates with factor activity level: severe (<1%), moderate (1–5%), mild (5–40%). Treatment centers on replacing the missing factor — factor VIII concentrate for hemophilia A, factor IX concentrate for hemophilia B. Desmopressin (DDAVP) can boost factor VIII levels in mild hemophilia A only. Nursing priorities include avoiding IM injections, aspirin, NSAIDs, and any activity that risks joint or internal trauma. Apply prolonged pressure to venipuncture sites. Teach families to recognize early hemarthrosis: joint warmth, swelling, decreased ROM, and pain with movement.

Key Distinctions

Don't confuse hemophilia (prolonged aPTT, normal PT, deep bleeding) with thrombocytopenia (low platelets, petechiae, mucosal bleeding) — hemophilia is a coagulation cascade problem, not a platelet problem. Students mix up DDAVP use: it works for mild hemophilia A only, not hemophilia B. A prolonged aPTT with normal PT points to the intrinsic pathway (factors VIII, IX) — a prolonged PT with normal aPTT points to the extrinsic pathway (factor VII, warfarin effect).

Clinical Pearl

Hemophilia bleeds deep, thrombocytopenia bleeds superficial. If you see hemarthrosis and a prolonged aPTT with normal platelets, think missing clotting factor, not missing platelets.