A software engineer presents to the outpatient department with easy fatiguability. He gives a history of sitting in front of the computer for 12-14 hours. He consumes a lot of junk food with very less fruits and vegetables. Hb is 9gm/dl and MCV 80 gl. What is the most likely cause of this patient’s anemia?

Correct Answer: A. Iron deficiency

Iron deficiency anemia is the most likely diagnosis in this patient based on the clinical presentation and laboratory findings. The key discriminating feature is the microcytic anemia (MCV 80 fL, normal 80–100 fL) with hemoglobin 9 g/dL. The patient's lifestyle and dietary history are crucial: prolonged sedentary work, consumption of junk food with minimal fruits and vegetables indicates poor dietary iron intake. In India, iron deficiency anemia remains the most common cause of anemia, particularly in vegetarian populations with limited bioavailable iron sources. The microcytic, hypochromic pattern (low MCV) is pathognomonic for iron deficiency—iron is essential for heme synthesis, and its deficiency leads to reduced hemoglobin production and smaller RBCs. The absence of neurological symptoms (which would suggest B12 deficiency) and the absence of jaundice or splenomegaly (which would suggest hereditary spherocytosis) further support iron deficiency. According to Robbins and Harrison, iron deficiency presents with microcytic anemia, low serum ferritin, and elevated TIBC; the dietary history here is the clinical pearl pointing directly to iron deficiency as the etiology.

Why the other options are wrong

B. Folic acid deficiency — Folic acid deficiency causes macrocytic anemia (MCV >100 fL), not microcytic. While the patient's poor diet could theoretically lack folate, the MCV of 80 fL rules this out definitively. Folic acid deficiency also presents with megaloblastic changes on blood smear and elevated homocysteine, neither of which fit this presentation. NBE trap: students may assume 'poor diet' automatically means folate deficiency, ignoring the MCV. C. Hereditary spherocytosis — Hereditary spherocytosis is a hemolytic anemia, not a nutritional deficiency, and presents with normocytic anemia (MCV 80–100 fL). The clinical clue is the absence of jaundice, dark urine, splenomegaly, or family history. HS would show spherocytes on blood smear, elevated reticulocyte count, and elevated indirect bilirubin—none mentioned here. This is a genetic disorder unrelated to dietary intake. D. Cyanocobalamin deficiency — Vitamin B12 deficiency causes macrocytic anemia (MCV >100 fL) with megaloblastic changes, not microcytic anemia. The patient lacks neurological symptoms (paresthesia, ataxia, dementia) that typically accompany B12 deficiency. While vegetarians are at risk for B12 deficiency in India, the MCV of 80 fL is incompatible with this diagnosis. NBE trap: conflating 'poor diet' with B12 deficiency in vegetarians, ignoring the microcytic pattern.

High-Yield Facts

Mnemonics

MCV-Based Anemia Classification (IRON-MAC-NORM) IRON (Microcytic, <80): Iron deficiency, Thalassemia, Sideroblastic anemia. MAC (Macrocytic, >100): B12 deficiency, Folate deficiency, Alcohol. NORM (Normocytic, 80–100): Hemolysis, Acute bleed, Renal failure, Marrow aplasia. Use MCV as your first filter—it eliminates 2/3 of options immediately. Iron Deficiency Red Flags (DIET-BLEED-ABSORB) DIET: Poor intake (vegetarian, junk food). BLEED: GI bleed, menorrhagia, hookworm (India). ABSORB: Celiac, post-gastrectomy. This patient has DIET as the obvious culprit.

NBE Trap

NBE pairs "poor diet" with multiple nutritional deficiencies (B12, folate) to distract from the MCV—the single most discriminating lab value. Students who skip the MCV and jump to "vegetarian = B12 deficiency" fall into this trap. Always read the MCV first.

Clinical Pearl

In Indian outpatient practice, iron deficiency anemia is so common that it is often the default diagnosis in microcytic anemia until proven otherwise. A simple serum ferritin and TIBC confirm the diagnosis; iron supplementation (ferrous sulfate 200 mg BD with vitamin C for absorption) is the DOC and should show reticulocytosis within 3–5 days if iron deficiency is correct.

_Reference: Robbins Ch. 13 (Red Blood Cell Disorders); Harrison Ch. 97 (Anemia); KD Tripathi Ch. 8 (Hematopoiesis & Anemias)_