Anemia

The exam rarely asks “what is anemia”; it tests whether you can match the anemia type to its lab and intervention. The classic tell is a microcytic, hypochromic (low MCV) picture pointing to iron deficiency, versus a macrocytic (high MCV) picture that splits into B12 versus folate — and the trap is that only B12 deficiency causes neurologic signs (paresthesias, ataxia), so giving folate alone can correct the anemia while nerve damage silently progresses. For oral iron teaching: take with vitamin C on an empty stomach, expect harmless dark stools, and use a straw for liquid forms (prevents tooth staining). Pernicious anemia (no intrinsic factor) classically needs lifelong IM B12, not pills.

Distinguish anemia from its siblings: anemia is a carrying-capacity problem (too little hemoglobin), hypoxia is low tissue oxygen, perfusion is delivery (cardiac output and flow), shock is failed perfusion. A severely anemic patient can show a normal SpO2 yet still be hypoxic, because pulse oximetry reads saturation percentage, not total oxygen content — hence the exertional dyspnea.