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Vitamin B12 deficiency — DCH MCQ

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HardGrowth and nutritionVitamin B12 deficiencyDCH

A 3-year-old child has followed a strictly vegan diet since weaning and has not received vitamin B12 supplementation. They have fatigue, poor growth, glossitis and recent developmental regression. The full blood count shows macrocytic anaemia with mild neutropenia and thrombocytopenia; the blood film shows macro-ovalocytes and hypersegmented neutrophils. Serum folate is normal. Before starting replacement, which is the most appropriate initial biochemical investigation?

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Correct answer: D — Serum total vitamin B12

The correct answer is D, serum total vitamin B12. An unsupplemented vegan diet, glossitis, developmental regression and megaloblastic blood-film changes strongly suggest nutritional vitamin B12 deficiency. The initial biochemical investigation is measurement of total vitamin B12, ideally on a sample taken before replacement. Serum methylmalonic acid is most useful when the initial vitamin B12 result is indeterminate or conflicts with strong clinical suspicion; homocysteine is less specific because folate deficiency and other conditions can also increase it. Anti-intrinsic factor antibody investigates autoimmune malabsorption after deficiency is identified and is not the first test in a young child with an evident dietary risk. Bone marrow examination is unnecessarily invasive when the clinical and haematological pattern supports a nutritional megaloblastic anaemia. Treatment should not be delayed if neurological deterioration is clinically significant.

Reference: NHS. Vitamin B12 or folate deficiency anaemia – Diagnosis. Reviewed 20 February 2023. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/diagnosis/