A clinician is evaluating five adult patients who present with generalized fatigue and are… — USMLE Step 3

A clinician is evaluating five adult patients who present with generalized fatigue and are found to have hemoglobin levels between $8.5$ and $10.2 \text{ g/dL}$ . Match each of the following detailed laboratory profiles to the most likely underlying hematologic diagnosis.

MCV $72 \text{ fL}$ , Serum Iron $30 \mu\text{g/dL}$ , TIBC $450 \mu\text{g/dL}$ , Ferritin $12 \text{ ng/mL}$ , Reticulocyte count $0.5\%$ Iron deficiency anemia
MCV $76 \text{ fL}$ , Serum Iron $40 \mu\text{g/dL}$ , TIBC $210 \mu\text{g/dL}$ , Ferritin $650 \text{ ng/mL}$ , Reticulocyte count $1.2\%$ Anemia of chronic disease
MCV $65 \text{ fL}$ , Serum Iron $110 \mu\text{g/dL}$ , TIBC $300 \mu\text{g/dL}$ , Ferritin $250 \text{ ng/mL}$ , RBC count $5.8 \times 10^6/\mu\text{L}$ Beta-thalassemia trait
MCV $108 \text{ fL}$ , Reticulocyte count $6\%$ , LDH $850 \text{ U/L}$ , Haptoglobin $< 10 \text{ mg/dL}$ , Indirect Bilirubin $3.2 \text{ mg/dL}$ Autoimmune hemolytic anemia
MCV $112 \text{ fL}$ , Reticulocyte count $0.4\%$ , LDH $180 \text{ U/L}$ , Methylmalonic acid elevated, Homocysteine elevatedVitamin B12 deficiency

Answer

Profile 1 matches Iron deficiency anemia, Profile 2 matches Anemia of chronic disease, Profile 3 matches Beta-thalassemia trait, Profile 4 matches Autoimmune hemolytic anemia, and Profile 5 matches Vitamin B12 deficiency.

Each specific diagnosis produces a distinct laboratory signature reflecting its underlying pathophysiology. Iron deficiency shows absolute iron depletion (low ferritin, high TIBC), while anemia of chronic disease features hepcidin-mediated iron sequestration (high ferritin, low TIBC). Thalassemia trait causes severe microcytosis with an elevated RBC count and normal iron stores. Hemolysis is defined by red cell destruction (high LDH, low haptoglobin, reticulocytosis), whereas Vitamin B12 deficiency causes defective DNA synthesis leading to macrocytosis with hypoproliferation and elevated specific metabolites (methylmalonic acid and homocysteine).

Step-by-Step Solution

Analyze MCV and iron indices to categorize microcytic anemias.

Profiles 1, 2, and 3 are microcytic. High TIBC and low ferritin identify iron deficiency (Profile 1). Low TIBC and high ferritin identify chronic disease (Profile 2). Normal iron stores with an elevated RBC count identify thalassemia trait (Profile 3).

Differentiating microcytic anemias requires evaluating total body iron stores and distribution via ferritin, TIBC, and serum iron.

Evaluate reticulocyte count and hemolysis markers to categorize macrocytic anemias.

Profiles 4 and 5 are macrocytic. High reticulocytes, high LDH, and low haptoglobin indicate active destruction or hemolysis (Profile 4). Low reticulocytes with elevated methylmalonic acid and homocysteine indicate defective DNA synthesis due to cobalamin deficiency (Profile 5).

Macrocytic anemias are broadly divided into hemolytic (hyperproliferative) and megaloblastic (hypoproliferative) categories.

Key Concept

Interpreting comprehensive hematologic panels to differentiate mechanisms of anemia.

Alternative Method

The Mentzer index (MCV divided by RBC count) can rapidly differentiate thalassemia trait from iron deficiency anemia in microcytic presentations. An index

< 13

strongly suggests thalassemia trait, whereas

> 13

suggests iron deficiency. For Profile 3, the index is

65 / 5.8 = 11.2

Estimated Time:1m 30s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Alternative Method

Topics

More questions from this topic