A 55-year-old woman presents with fatigue, numbness in her hands and feet, and difficulty maintaining balance. Blood tests show macrocytic anaemia with low haemoglobin and an elevated MCV. Which deficiency is indicated?

• A. Vitamin B6 deficiency
• B. Folate deficiency
• C. Vitamin B12 (cobalamin) deficiency
• D. Iron deficiency

Answer: (C)

Macrocytic anemia with neurological symptoms most strongly points to vitamin B12 (cobalamin) deficiency. Vitamin B12 is essential for proper DNA synthesis in rapidly dividing cells and for myelin formation in the nervous system. When B12 is lacking, red blood cell precursors can’t mature normally, leading to enlarged red blood cells and an elevated MCV (macrocytosis). At the same time, insufficient B12 disrupts myelin, causing numbness or tingling and balance or gait difficulties from dorsal column and corticospinal tract involvement.

Folate deficiency can also cause macrocytosis because it similarly impairs DNA synthesis, but it does not typically cause the neurological symptoms seen here. Iron deficiency causes microcytic anemia (low MCV), not macrocytosis. Vitamin B6 deficiency can cause neuropathy but usually presents with microcytic or normocytic anemia rather than macrocytosis.

So the pattern of macrocytosis plus neuro symptoms fits B12 deficiency best, with consideration for causes like pernicious anemia or malabsorption.