A 51-year-old woman who is 10 years after gastric bypass presents with numbness and tingling in the distal lower extremities and significant anemia with neutropenia, but normal vitamin B12, iron, ferritin, and transferrin. Which nutritional deficiency is the most likely cause of these findings?

• A. Thiamin
• B. Zinc
• C. Folate
• D. Copper

Answer: (D)

Copper deficiency is the best fit because copper is essential for both iron metabolism and nervous system integrity. After gastric bypass, malabsorption can reduce copper absorption, leading to low copper stores over time. Copper is a cofactor for enzymes like ceruloplasmin and hephaestin that oxidize iron so it can be loaded onto transferrin and used by the bone marrow. When copper is deficient, iron mobilization is impaired, causing anemia, and myeloid cell maturation is affected, producing neutropenia. Neurologic symptoms such as numbness and tingling in the distal limbs reflect demyelination and neuropathy from copper’s role in myelin maintenance.

The normal vitamin B12 level and normal iron/ferritin/transferrin help distinguish this from B12 or iron-deficiency anemias; copper deficiency can present with anemia and neutropenia despite these values being normal. Folate deficiency would more predict macrocytic anemia with different neurologic features, and thiamin deficiency would typically show different systemic clues. In the context of bariatric surgery, copper deficiency is a classic cause of this combination of neuropathy and hematologic abnormalities.