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PA16.1-3 | Hemolytic Anemias — Case Study

CLINICAL SCENARIO

A 19-year-old male student presents to the emergency department with sudden-onset fatigue, scleral icterus, and left-sided abdominal discomfort after a three-day course of co-trimoxazole for a urinary tract infection. Examination reveals pallor, jaundice, and a spleen palpable 4 cm below the costal margin. Hb 6.8 g/dL, MCV 88 fL, reticulocyte count 11%, total bilirubin 4.2 mg/dL (indirect 3.6), LDH 890 U/L, haptoglobin undetectable. Peripheral smear shows bite cells, blister cells, and rare Heinz bodies on methyl-violet stain. DAT (Coombs) is negative. You are the junior doctor on call.

Instructions

Work through this haemolytic crisis systematically using the five-section scaffold below. Use clinical reasoning, not only pattern-matching. In Section 1, confirm and quantify haemolysis using the laboratory markers presented. In Section 2, classify whether haemolysis is intravascular or extravascular — and explain why both patterns are present here. In Section 3, apply the peripheral smear findings and DAT result to reach a specific diagnosis. In Section 4, integrate the SDL knowledge (SDL1 classification, SDL2 hereditary defects, SDL3 acquired triggers) to explain the pathophysiology at a cellular level. In Section 5, outline the immediate management and long-term counselling you would provide. Cite evidence or textbook references where appropriate. Target approximately 1,400–1,700 words across all sections.

Length: Target 1,400–1,700 words total. Suggested distribution: Section 1 ~250 w, Section 2 ~250 w, Section 3 ~250 w, Section 4 ~350 w, Section 5 ~300 w, Section 6 ~150–200 w. Do not exceed 1,800 words — reviewers are instructed to flag verbosity as a quality issue.

What to Submit

Section 1 — Confirm Haemolysis: Interpreting the Laboratory Markers

Using the laboratory values given in the case, identify and interpret each marker of haemolysis. Explain what each marker tells you mechanistically, and state whether the overall picture confirms intravascular haemolysis, extravascular haemolysis, or both. Include: reticulocyte count, bilirubin fractions, LDH, and haptoglobin.

Guidance: Draw on SDL1 (classification and laboratory markers of haemolysis). A strong answer will correctly interpret undetectable haptoglobin and elevated indirect bilirubin as complementary evidence, explain why the bone marrow response (retics 11%) may lag by 2–3 days, and note that LDH elevation alone is non-specific but its pattern here is consistent with red-cell destruction.

Section 2 — Localise the Site: Intravascular vs Extravascular

Explain the distinction between intravascular and extravascular haemolysis. Based on the clinical and laboratory findings, determine which mechanism(s) are operative in this patient. Justify your reasoning with reference to the specific lab values and the smear morphology (bite cells, blister cells).

Guidance: SDL1 and SDL3 material. The key insight is that G6PD-deficiency haemolysis is predominantly intravascular (oxidant damage → Heinz body formation → pitting by spleen → bite/blister cells with intravascular leak). A strong answer will note the splenomegaly as evidence of ongoing extravascular clearance of damaged cells and explain the Heinz-body pitting mechanism.

Section 3 — Reach a Specific Diagnosis Using the Smear and DAT

Using the peripheral smear findings (bite cells, blister cells, Heinz bodies) and the negative DAT result, narrow the differential and arrive at the most likely diagnosis. Explain why AIHA and immune-mediated haemolysis have been effectively excluded. State the most probable diagnosis and identify the precipitating factor.

Guidance: SDL2 (hereditary haemolytic anaemias) and SDL3 (acquired haemolysis). The negative DAT excludes AIHA; the morphology with Heinz bodies after drug exposure (co-trimoxazole is an oxidant drug triggering haemolysis in G6PD deficiency) is classic. Students should name glucose-6-phosphate dehydrogenase deficiency explicitly and identify the drug as the trigger. Distinguish from sickle-cell crisis (no sickle cells, HbS negative, different morphology).

Section 4 — Pathophysiology at the Cellular Level (SDL Integration)

Explain how G6PD deficiency leads to vulnerability to oxidant stress. Trace the molecular chain from enzyme deficiency → reduced GSH → Heinz body formation → red-cell membrane damage → haemolysis. Briefly contrast the pathophysiology with that of hereditary spherocytosis (SDL2) and warm AIHA (SDL3) to show you understand how different mechanisms produce different smear appearances.

Guidance: This is the conceptual integration section. A distinguished answer will explain the role of the hexose monophosphate shunt, NADPH generation, glutathione reduction, and oxidant damage in sequence. The contrast with spherocytosis (spectrin/ankyrin defect → loss of membrane → spherical shape → splenic trapping) and warm AIHA (IgG opsonisation → macrophage Fc-receptor clearance) reinforces SDL cross-linking and demonstrates classification fluency.

Section 5 — Management and Long-Term Counselling

Outline the immediate management for this patient and the long-term counselling you would provide. Address: (a) immediate supportive care and indications for transfusion; (b) when to test for G6PD enzyme activity and how to interpret the result during an acute crisis; (c) the drugs, foods, and clinical situations the patient must avoid for life; (d) genetic implications and family screening.

Guidance: SDL3 (acquired triggers, management). Key teaching points: G6PD enzyme assay during crisis may be falsely normal (young reticulocytes have higher activity) — retest after 3 months. Folic acid supplementation if recurrent. Drugs to avoid: primaquine, dapsone, high-dose aspirin, nitrofurantoin, co-trimoxazole. Foods: fava beans. X-linked inheritance — counsel about maternal carrier status and male siblings. Transfusion threshold ~7 g/dL with symptoms or cardiorespiratory compromise.

Section 6 — Reflection: What Would Change If the DAT Were Positive?

Briefly reflect on how your diagnostic reasoning would have changed if the DAT had been positive rather than negative. What diagnosis would you have prioritised? How would the management differ? What does this case teach you about the systematic approach to haemolytic anaemia?

Guidance: Open-ended reflection on diagnostic reasoning under uncertainty. A warm AIHA would have been the priority with a positive DAT — management would then include corticosteroids, not just stopping the offending drug. Assessing whether students can reason counterfactually tests higher-order thinking (Bloom's analysis/evaluation). Keep this section concise (150–200 words).

Grading Rubric — Hemolytic Anaemias Case-Study Rubric (30 points)

Criterion	Points	Full-marks descriptor
Section 1 — Laboratory Interpretation of Haemolysis Markers	5 pts	All four markers (retics, bilirubin fractions, LDH, haptoglobin) correctly interpreted with mechanistic reasoning; bone-marrow lag and non-specificity of LDH acknowledged; clear conclusion on haemolysis pattern.
Section 2 — Localisation: Intravascular vs Extravascular Haemolysis	5 pts	Distinction between intra- and extravascular haemolysis is precisely defined; both mechanisms correctly identified as operative; Heinz-body pitting mechanism and splenomegaly explained with integration of smear morphology.
Section 3 — Specific Diagnosis via Smear and DAT Interpretation	5 pts	G6PD deficiency named explicitly as the diagnosis; negative DAT used to exclude AIHA with correct reasoning; co-trimoxazole correctly identified as the oxidant trigger; sickle-cell excluded with morphological evidence.
Section 4 — Cellular Pathophysiology and SDL Cross-Integration	7 pts	Complete mechanistic chain (HMP shunt → NADPH → GSH → oxidant damage → Heinz bodies → haemolysis) explained accurately; contrast with spherocytosis and warm AIHA is precise and demonstrates SDL cross-integration; Year-2-appropriate depth throughout.
Section 5 — Management and Long-Term Counselling	5 pts	Immediate management correct including transfusion threshold; timing caveat for G6PD assay during crisis explicitly stated; comprehensive list of avoidance triggers; X-linked inheritance and family screening addressed.
Section 6 — Counterfactual Reflection and Diagnostic Reasoning	3 pts	Warm AIHA correctly prioritised for positive-DAT scenario; management difference (corticosteroids vs drug withdrawal) clearly articulated; genuine reflection on systematic approach to haemolysis differential.

PEER REVIEW

You will review a peer's response to the same haemolytic anaemia case. Your review should be constructive, specific, and evidence-based. Use the rubric to guide your assessment, but your written feedback must go beyond a score — identify at least two strengths and two areas for improvement. For each area for improvement, suggest a specific correction or addition the student could make. Keep your review between 250–400 words. Do not comment on grammar or presentation unless it impedes comprehension. Focus on scientific accuracy, mechanistic reasoning, and clinical applicability. Submit your review within 48 hours of receiving the assignment.