Questions: Anemia: Classification and Pathophysiology

Question 1

A patient has hemoglobin 9.2 g/dL, MCV 68 fL, elevated serum ferritin, low-normal serum iron, and normal TIBC. Which diagnosis is most consistent with this pattern?

• A. Iron deficiency anemia — all microcytic anemia is caused by iron deficiency
• B. Anemia of chronic disease — elevated ferritin with low serum iron suggests iron is sequestered, not depleted
• C. Megaloblastic anemia — the MCV indicates a DNA synthesis defect
• D. Hemolytic anemia — the low hemoglobin indicates accelerated destruction

Answer: (B)

Microcytic anemia (low MCV) reflects impaired hemoglobin synthesis, but the cause must be specified. Classic iron deficiency produces low ferritin and high TIBC. Here, ferritin is elevated and TIBC is normal — the pattern of anemia of chronic disease, in which iron is sequestered in stores and unavailable for erythropoiesis. Option A is the classic misconception: microcytosis is not synonymous with iron deficiency. Thalassemia trait and chronic disease are equally important causes. Megaloblastic anemia has a high MCV, not low. Hemolytic anemia is typically normocytic with an elevated reticulocyte count.

Question 2

In chronic anemia, 2,3-DPG accumulates within red blood cells. What is the primary functional consequence?

• A. It increases hemoglobin synthesis to compensate for reduced red cell mass
• B. It shifts the oxygen-dissociation curve rightward, making it easier to unload oxygen to tissues
• C. It signals the kidneys to increase erythropoietin production
• D. It shifts the oxygen-dissociation curve leftward, allowing hemoglobin to bind oxygen more tightly

Answer: (B)

2,3-DPG binds to deoxyhemoglobin and stabilizes the T (tense, low-affinity) state, shifting the oxygen-dissociation curve rightward — hemoglobin releases oxygen more readily at any given partial pressure. When total hemoglobin is low, the body extracts more oxygen from each red cell by reducing hemoglobin's affinity. Option D inverts the effect: a leftward shift would increase affinity and impair delivery. 2,3-DPG does not stimulate erythropoietin (that is a kidney/hypoxia response) or hemoglobin synthesis directly.

Question 3

A patient with hemoglobin of 9.0 g/dL will invariably experience significant dyspnea and fatigue, because this level is below the normal range.

• T. True
• F. False

Answer: False

Tolerance of anemia depends critically on whether it developed acutely or chronically. Chronic anemia allows time for compensatory mechanisms — increased 2,3-DPG, rightward shift in the oxygen-dissociation curve, increased cardiac output, and upregulated erythropoietin — to develop. A patient who has gradually reached 9.0 g/dL may be largely asymptomatic. Acute anemia at the same level (e.g., from hemorrhage) can be dangerous because compensations haven't had time to develop. The hemoglobin value alone does not determine symptoms.

Question 4

In hemolytic anemia, the reticulocyte count is typically elevated because the bone marrow is responding to accelerated red cell destruction by increasing production.

• T. True
• F. False

Answer: True

Reticulocytes are immature red cells released from the bone marrow. In hemolytic anemia, red cells are destroyed faster than normal, causing hypoxic signaling that drives increased erythropoietin release and accelerated marrow output. The elevated reticulocyte count confirms that the marrow is functional and responding appropriately — distinguishing hemolytic anemia from aplastic processes where the marrow fails to respond. Normocytic anemia with high reticulocyte count is the hallmark pattern of hemolysis or acute blood loss.

Question 5

Why does classifying anemia by MCV (microcytic, normocytic, or macrocytic) help identify the underlying cause, rather than simply confirming that hemoglobin is low?

Model answer: MCV reflects the size of red blood cells, which is determined by where in the production pathway the defect lies. Microcytic cells (low MCV) indicate impaired hemoglobin synthesis — cells divide more than normal before reaching a critical hemoglobin concentration, producing smaller cells. This points toward iron deficiency, anemia of chronic disease, or thalassemia. Macrocytic cells (high MCV) indicate impaired DNA synthesis — the cell grows in cytoplasm but cannot divide normally, producing large cells. This points toward B12 or folate deficiency. Normocytic anemia with low reticulocyte count points toward marrow failure; with high reticulocyte count it points toward hemolysis or acute blood loss. MCV is the first branch in a diagnostic algorithm that routes the workup toward the specific underlying cause, each requiring its own treatment.

Anemia is a sign, not a diagnosis. The underlying cause determines the treatment. MCV provides the first crucial branching point by revealing which step in red cell production has failed, directing targeted testing and avoiding unnecessary workup.