OSCE STATION 9. Hemostasis Disorders — Coagulation Interpretation, Management & Thrombosis Prevention

Candidate instructions

Review the child’s history and investigation sheet. Interpret each bleeding parameter, identify the likely disorder, explain your diagnostic approach and immediate management, and calculate an initial factor VIII dose for the stated target level. Answer the examiner’s brief questions about other bleeding disorders and thrombosis prevention.

Clinical setting and requirements

You are in a pediatric emergency department. A 7-year-old child weighing 20 kg has a painful, swollen knee after a minor fall. Materials: the clinical history and investigation sheet below, and a calculator. No patient examination or simulated patient is required.

Expected student performance

1. Identify the bleeding pattern: joint bleeding after minor trauma suggests a coagulation-factor disorder. Ask about previous joint or muscle bleeds, bleeding after procedures, medicines, family history, and current head injury or other major bleeding.
2. Interpret platelet count, bleeding time (BT), clotting time (CT), prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, and fibrin degradation products (FDPs) together. Explain what each tests and the limitations of BT and CT.
3. State the likely diagnosis and confirmatory factor assays. Consider a mixing study or inhibitor assessment if the pattern or treatment response warrants it.
4. Arrange prompt intravenous factor VIII for the suspected joint bleed, calculate the initial dose, and seek pediatric hematology advice for assessment, monitoring, repeat dosing, and longer-term prophylaxis.
5. Explain how management changes for a significant accident, bleeding around a deciduous tooth, or planned surgery. Distinguish this pattern from von Willebrand disease (VWD), immune thrombocytopenia (ITP), and consumptive coagulopathy.
6. Classify inherited and acquired hypercoagulable states; outline risk-based thrombosis prevention and the response to suspected venous thromboembolism.

Station findings and investigation sheet

The child has had two previous episodes of swelling in the same knee. A maternal uncle has a history of excessive bleeding. The child is alert, with no reported head strike. The knee is warm, swollen, and painful on movement; there is no external wound.

BT and CT appear on this teaching sheet because they are assigned curriculum parameters. Modern assessment relies on the bleeding history and appropriate laboratory tests rather than these historical measurements.

Model interpretation and clinical conclusion

The recurrent hemarthroses, maternal family history, isolated prolonged aPTT, and factor VIII activity of 2 IU/dL indicate moderate hemophilia A with an acute knee bleed. Give factor VIII intravenously promptly and assess the joint and neurovascular status. One IU/kg of standard half-life factor VIII raises activity by approximately 2 IU/dL; therefore:

Initial dose = 20 kg × (50 − 2) IU/dL × 0.5 = 480 IU IV, approximately 500 IU according to available vial size and the treating team’s protocol. Check clinical response and factor activity; subsequent doses depend on recovery, product, and bleed severity.

For a significant accident, particularly possible head injury, arrange immediate factor replacement and urgent assessment without waiting for imaging. For uncomplicated natural shedding of a deciduous tooth, use local pressure if needed; persistent bleeding or planned extraction requires a hematology and dental plan, often including local measures and tranexamic acid, with factor cover when indicated. Surgery requires a preoperative factor plan, higher procedure-specific targets, and postoperative activity monitoring.

Diagnostic approach to other bleeding presentations: mucocutaneous bleeding suggests platelet or VWF dysfunction; joint or deep-muscle bleeding suggests a factor deficiency; prolonged PT and aPTT with low fibrinogen and raised FDPs suggests consumption such as disseminated intravascular coagulation. Take a focused bleeding and drug history, examine for severity, obtain a full blood count and coagulation screen, then order directed factor, VWF, or platelet testing.

Critical safety points

Treat suspected intracranial or other life-threatening bleeding immediately with appropriate factor replacement while arranging emergency care. Avoid intramuscular injections and medicines that impair platelet function when alternatives are available. If bleeding fails to respond as expected, urgently consider a factor VIII inhibitor.

Examiner viva

1. What does the coagulation screen assess?
   Platelet count assesses platelet number; PT assesses the extrinsic and common pathways; aPTT assesses the intrinsic and common pathways; fibrinogen measures available clotting substrate; raised FDPs indicate fibrin or fibrinogen breakdown. BT and CT have limited clinical reliability.
2. How would you manage VWD?
   Use local measures and tranexamic acid for appropriate mucosal bleeding; consider desmopressin only when the VWD type and documented response support it, with attention to fluid restriction and hyponatremia. Give VWF-containing concentrate for severe bleeding or major procedures when indicated.
3. How would you manage a child with ITP?
   Confirm isolated thrombocytopenia and assess bleeding severity. Observe a well child with no or minor bleeding; discuss treatment such as a short corticosteroid course or IVIG for more significant bleeding with hematology. Severe, life-threatening hemorrhage needs emergency specialist treatment.
4. How are hypercoagulable states classified?
   Inherited examples include factor V Leiden and antithrombin, protein C, or protein S deficiency. Acquired risks include surgery, immobility, cancer, estrogen exposure, and antiphospholipid syndrome.
5. How do you prevent and manage thrombosis?
   Assess clotting and bleeding risks, encourage appropriate early mobility, and use mechanical or pharmacological prophylaxis when indicated. Investigate suspected deep-vein thrombosis or pulmonary embolism promptly and start therapeutic anticoagulation when clinically appropriate.