Micronutrient deficiencies — formative SAQs

SAQ 1 — The iron-deficient toddler (20 marks, ~15 minutes)

A two-year-old boy is referred with pallor, tiredness and irritability over three months. His mother reports that he eats little solid food, drinks around eight hundred millilitres of cow's milk a day, and has recently begun eating handfuls of garden soil. His weight has fallen from the fiftieth to the fifteenth centile. A full blood count shows a haemoglobin of eighty-two grams per litre with a mean cell volume of sixty-two femtolitres. ^[1]

Questions

1. Give the most likely diagnosis and the three features of the history and blood film that support it. (5 marks) ^[1]
2. Outline the confirmatory iron studies and explain why a C-reactive protein must accompany the ferritin. (5 marks) ^[1]
3. Outline the management, including the oral iron dose, the expected timeline of response and the dietary advice. (5 marks) ^[2]
4. Give the differential diagnosis of microcytic anaemia and the single feature that best separates iron deficiency from thalassaemia trait. (3 marks) ^[1]
5. Explain the rationale for universal iron screening at around twelve months. (2 marks) ^[1]

Model answer (must-hit)

1. The most likely diagnosis is iron-deficiency anaemia. The supporting features are the microcytic anaemia on the blood film with a low mean cell volume, the pallor and fallen growth centile, and the dietary history of excessive cow's milk intake with pica, the eating of soil, which is a classic clue. ^[1]
2. The confirmatory tests are a low serum ferritin, a low transferrin saturation, a raised transferrin and a low reticulocyte count. The C-reactive protein is required because ferritin is an acute-phase reactant that rises with inflammation and can mask iron deficiency, so a normal ferritin in a sick or inflamed child does not exclude it. ^[1]
3. The management is oral elemental iron at around three milligrams per kilogram per day, with dietary advice to limit cow's milk to around five hundred millilitres a day and introduce iron-rich solids. The reticulocyte count should rise within one to two weeks, the haemoglobin should normalise within two to three months, and the iron should be continued for about three months after the haemoglobin normalises to replete the stores. ^[2]
4. The differential of microcytic anaemia is iron deficiency, thalassaemia trait, anaemia of chronic disease, lead poisoning and sideroblastic anaemia. The feature that best separates iron deficiency from thalassaemia trait is the serum ferritin, which is low in iron deficiency and normal or raised in thalassaemia trait, alongside a normal or near-normal haemoglobin and a positive family history in thalassaemia. ^[1]
5. Universal iron screening at around twelve months is recommended because iron deficiency harms the developing brain, through dopamine and myelination, before the anaemia appears, so waiting for pallor is waiting too long. The neurodevelopmental argument, not the anaemia alone, is the case for screening. ^[1]