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PA20.1-2 | Hemostasis & Bleeding Disorders — Case Study
CLINICAL SCENARIO
You are a junior doctor in the haematology outpatient clinic. A 10-year-old boy is brought by his mother with recurrent, painful swelling of the right knee after minor falls. His maternal uncle reportedly had 'a blood problem'. This case-study assignment asks you to apply your knowledge of the coagulation cascade, coagulation tests, platelet function, and factor deficiencies to classify the bleeding pattern, interpret the laboratory panel, and arrive at a specific diagnosis with a defensible management plan.
Instructions
Work through all six sections in order. Each section builds on the previous one, mirroring the clinical reasoning process. Cite specific mechanisms from your SDL modules (SDL1: coagulation cascade and tests; SDL2: platelet disorders; SDL3: factor deficiencies; SDL4: DIC and vitamin K disorders) when directed. Aim for precision — avoid vague statements like 'there is a clotting problem'. Your submission will be peer-reviewed by a classmate before faculty marking; write with enough clarity for another Year-2 student to follow your reasoning.
Length: Total 900–1200 words across all six sections. Suggested allocation: Section 1 — 150 words; Section 2 — 150 words (including table); Section 3 — 100 words; Section 4 — 150 words; Section 5 — 200 words; Section 6 — 200 words. Tables and diagrams do not count toward the word limit.
What to Submit
Section 1 — Bleeding Pattern Classification
Classify this patient's bleeding pattern as primary (platelet/vascular) or secondary (coagulation factor) haemostasis defect, with justification. List at least THREE clinical features in this presentation that distinguish one pattern from the other, and explain the pathophysiological basis for each.
Guidance: Think about WHERE and WHEN bleeding occurs, and how it relates to primary plug formation versus fibrin clot stabilisation. Refer to the haemostasis cascade overview from SDL1. Deep tissue bleeding (muscles, joints) versus mucocutaneous bleeding (petechiae, gum bleeding) is the key discriminator. Haemarthrosis is almost never caused by platelet defects alone.
Section 2 — Coagulation Panel Interpretation
The following panel is available: Platelets 240 × 10⁹/L (normal), PT 13 s (normal, INR 1.0), aPTT 72 s (reference 25–35 s), Fibrinogen 3.1 g/L (normal), D-dimer 0.3 mg/L FEU (normal). Interpret each result systematically, then state which pathway(s) of the coagulation cascade are affected and which are intact. Draw a table with columns: Test | Result | Normal/Abnormal | Pathway tested.
Guidance: SDL1 covers the extrinsic (PT/INR), intrinsic (aPTT), and common (fibrinogen, thrombin time) pathways. An isolated prolonged aPTT with normal PT, normal platelets, and normal fibrinogen points exclusively to the intrinsic (contact activation / tenase) pathway. List the factors in this pathway. D-dimer and fibrinogen are normal — use this to explicitly exclude DIC and fibrinolysis.
Section 3 — The Mixing Study
A 1:1 mixing study is performed (patient plasma mixed with normal pooled plasma). The corrected aPTT is 34 s (normal). Explain: (a) what a mixing study tests and how to interpret correction vs. non-correction; (b) what the corrected result in this patient tells you about the mechanism of the aPTT prolongation; (c) which broad category of intrinsic-pathway defect this confirms.
Guidance: Mixing studies distinguish FACTOR DEFICIENCY (normal plasma supplies the missing factor → aPTT corrects into normal range) from INHIBITOR/ANTIBODY presence (antibody persists → aPTT remains prolonged even after mixing). Correction here confirms a deficiency, not an inhibitor. SDL3 discusses acquired inhibitors vs. congenital deficiencies.
Section 4 — Specific Diagnosis and Inheritance
Given all the above plus the family history (maternal uncle affected), state the most likely specific diagnosis. Identify the deficient factor, its gene locus, and the mode of inheritance. Explain why male children of carrier mothers are affected while their mothers are typically asymptomatic. If available laboratory assays confirmed the diagnosis, what would the Factor VIII activity level be expected to show?
Guidance: SDL3 covers haemophilia A (Factor VIII deficiency, X-linked recessive, F8 gene on Xq28) and haemophilia B (Factor IX deficiency). The sex-linked pedigree (maternal uncle → boy, mother unaffected) is the canonical X-linked recessive pattern. Severity classification: severe <1%, moderate 1–5%, mild 5–40% activity. A boy presenting with spontaneous haemarthrosis typically has severe disease (<1% FVIII).
Section 5 — Differential Diagnosis & SDL Integration
List THREE differential diagnoses you considered before arriving at Haemophilia A and explain why each was excluded using specific test results from this panel. For each differential, state which SDL module (SDL1–4) contains the distinguishing mechanism. Differentials to consider: von Willebrand Disease (Type 3), Haemophilia B, DIC, Vitamin K deficiency.
Guidance: A structured differential requires: the disease, its expected panel finding, and why this patient's panel rules it out. For example — VWD Type 3 would also prolong aPTT and may prolong bleeding time/PFA-100, but VWF antigen and activity would be near-zero (SDL2 covers VWD); Haemophilia B affects FIX (same pathway, same panel pattern) — only factor assay discriminates; DIC would show low platelets, prolonged PT, low fibrinogen, high D-dimer (SDL4); Vitamin K deficiency would prolong both PT and aPTT (SDL4).
Section 6 — Management Principles & Competency Integration
Outline the acute and long-term management of this patient. Address: (a) acute haemarthrosis management; (b) factor replacement therapy (type, dosing principle, target level); (c) prophylaxis rationale; (d) one complication of long-term factor replacement and how it is detected. Then write a single paragraph reflecting on how the coagulation cascade knowledge from SDL1 directly guided your laboratory interpretation and management choice in this case.
Guidance: Management integrates pathophysiology: the deficient factor must be replaced to reconstitute the intrinsic tenase complex and generate sufficient thrombin. RICE + joint protection for haemarthrosis. FVIII concentrates (recombinant preferred) target 50–100% activity for joint bleeds. Prophylaxis prevents joint arthropathy (haemophilic arthropathy, SDL3 complication). Inhibitor development (alloantibody to FVIII) occurs in ~30% of severe patients — detected by Bethesda assay. Your reflection should name the pathway, the test, the inference, and the therapeutic target.
Grading Rubric — H10 Case-Study Rubric — Haemostasis & Bleeding Disorders (30 points)
| Criterion | Points | Full-marks descriptor |
|---|---|---|
| Bleeding Pattern Classification (Sections 1): Accuracy and mechanistic depth of primary vs. secondary haemostasis distinction | 5 pts | Correctly classifies as secondary haemostasis defect. Provides three or more clinical features (haemarthrosis, deep muscle haematoma, absence of petechiae/purpura) each linked to a specific mechanism (platelet plug intact; fibrin clot deficient). SDL1 cascade language used precisely. |
| Coagulation Panel Interpretation (Section 2): Systematic interpretation of all five tests with pathway mapping | 6 pts | All five tests interpreted correctly (normal/abnormal) with accurate pathway assignment. Table is well-structured with four columns completed for every test. Correctly identifies isolated intrinsic pathway defect. Explicitly uses normal D-dimer and fibrinogen to exclude DIC/fibrinolysis. |
| Mixing Study Interpretation (Section 3): Correct explanation of the principle, correct interpretation of correction, correct category conclusion | 4 pts | Accurately explains mixing study principle (normal plasma dilutes or supplies missing factor). Correctly interprets correction as evidence of factor deficiency (not inhibitor). Names both possible outcomes (correction vs. non-correction) with examples of each clinical entity. Correctly concludes intrinsic pathway factor deficiency. |
| Specific Diagnosis and Genetics (Section 4): Precision of diagnosis, correct gene/inheritance, and expected assay result | 5 pts | Names Haemophilia A specifically. Identifies FVIII, F8 gene on Xq28, X-linked recessive. Accurately explains carrier mother / affected son mechanism using Lyonisation or allele logic. States expected FVIII activity <1% for severe disease. Family history correctly used as supporting evidence. |
| Differential Diagnosis with SDL Integration (Section 5): Quality and precision of three differentials with panel-based exclusion | 5 pts | Three correct differentials named. Each excluded with a specific panel result and mechanistic reason. Correct SDL module cited for each (e.g., VWD → SDL2; Haemophilia B → SDL3; DIC → SDL4; VitK → SDL4). Demonstrates understanding that Haemophilia B cannot be distinguished from A without factor assay. |
| Management and Reflection (Section 6): Clinical accuracy of management, depth of reflection on SDL-to-reasoning pathway | 5 pts | Addresses all four management elements: RICE + joint protection; recombinant FVIII concentrate with target 50–100% for acute haemarthrosis; prophylaxis rationale linked to preventing arthropathy; inhibitor complication named and Bethesda assay cited. Reflection paragraph explicitly connects cascade pathway → test → inference → therapeutic target. Shows integration across all four SDL modules. |
PEER REVIEW
You will receive a classmate's submission. Read their response to all six sections before scoring anything. Then:
1. Section 2 table check: Verify their five test interpretations and pathway assignments against your own. Note any discrepancy in comments.
2. Mixing study: Check if they correctly differentiated correction (deficiency) from non-correction (inhibitor). If confused, write one sentence explaining the distinction.
3. Diagnosis: Does their diagnosis match the panel evidence? If they named Haemophilia B instead of A, note that factor assay is required to distinguish — this is acceptable reasoning, not an error.
4. Strongest section: Identify the section where their clinical reasoning was clearest and say why (one sentence).
5. One constructive suggestion: Identify ONE place where adding a specific mechanism or SDL module reference would strengthen the submission.
Peer review score (5 marks separate from the main rubric): Award 5 if feedback is specific, evidence-based, and actionable; 4 if specific but one comment is vague; 3 if comments are mostly descriptive; 2 if feedback is a single sentence per section; 1 if feedback is only positive with no constructive critique.