Source / episode info

• **Episode:**83
• **Title:**Divine Intervention Episode 83 – USMLE Step 1 Hematology Review (Part 5)
• **Published:**2019-03-09
• Source:Episode page

One-liner

This episode provides a comprehensive review of key metabolic deficiencies (B12/Folate), iron handling (ID vs. ACD), and enzyme defects (G6PD, Pyruvate Kinase) that cause hemolytic anemia, while also covering the spectrum of microcytic anemias from thalassemia to lead poisoning.

High-yield summary

• B12 Absorption: B12 must be protected by R factor in the stomach, then cleaved by pancreatic enzymes in the duodenum, and finally absorbed via the intrinsic factor complex at the terminal ileum.
• Iron Deficiency vs. ACD: ID -> Low Ferritin, High TIBC; ACD -> High Ferritin, Low TIBC (due to inflammation sequestering iron).
• G6PD Testing: Must be performed weeks after the acute hemolytic episode has resolved, not during the crisis.
• Pyruvate Kinase Deficiency: Leads to increased 2,3-DPG production via BPG Mutase, causing a characteristic right shift of the oxyhemoglobin dissociation curve and hemolysis due to ATP depletion in RBCs.
• Lead Poisoning: Causes microcytosis, abdominal pain, and high ferritin/low TIBC (mimicking iron overload) because lead inhibits ferrochelatase and ALA dehydratase, leading to functional iron trapping.

Learning objectives

• Differentiate between macrocytic and microcytic anemia etiologies based on lab values (MCV, ferritin, TIBC).
• Trace the metabolic pathways for Vitamin B12 absorption and deficiency causes.
• Explain the biochemical basis of iron sequestration in chronic inflammation (ACD).
• Identify enzyme deficiencies causing hemolytic anemia (G6PD, Pyruvate Kinase) and their associated laboratory findings.
• Recognize classic clinical presentations and lab patterns for lead poisoning and thalassemia syndromes.

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