Iron deficiency anaemia — formative SAQs

SAQ 1 (10)

A 20-month-old boy is brought to the clinic with pallor and irritability over two months. His mother reports he drinks approximately 900 mL of cow's milk per day and eats very little solid food; cow's milk was introduced at 9 months. He was born at 36 weeks. On examination he is pale with a flow murmur, his weight is on the 10th centile, and he is haemodynamically stable. His haemoglobin is 72 g per litre with a mean cell volume of 64 fL, a mean cell haemoglobin of 20 pg, and a raised red cell distribution width. His ferritin is 4 micrograms per litre with a normal C-reactive protein. His mother mentions he constantly chews and swallows ice. ^[4][5]

1. Define iron deficiency anaemia using the WHO threshold for this child's age, and explain how the results confirm the diagnosis and the cause. (4) ^[1][3]
2. Explain the role of cow's milk and the ice-chewing behaviour in his presentation. (3) ^[4][5]
3. Outline the definitive management, including the dose, frequency, duration and expected response. (3) ^[3][8]

Model answer

Diagnosis and cause. Iron deficiency anaemia is the anaemia that results when iron stores fall too low to sustain haemoglobin synthesis, producing small pale red cells. The WHO threshold for a child aged 6 to 59 months is a haemoglobin below 110 g per litre, so this boy's haemoglobin of 72 g per litre is markedly below it. The low mean cell volume of 64 fL and mean cell haemoglobin of 20 pg confirm a microcytic hypochromic anaemia, the raised red cell distribution width supports iron deficiency over thalassaemia trait, and the ferritin of 4 micrograms per litre with a normal C-reactive protein confirms iron deficiency unambiguously. The Mentzer index would be expected to be over 13. The cause is dietary: the excessive cow's milk intake of 900 mL per day, the early introduction at 9 months, and the prematurity that left him with lower iron stores at birth. ^[1][3]

Cow's milk and pica. Cow's milk causes iron deficiency through three mechanisms: it is itself low in iron, its high calcium content blocks the absorption of iron from the rest of the diet, and the large volume displaces iron-rich solid foods so the child's overall iron intake collapses. In some children, cow's milk protein also induces a subtle enteropathy with occult gastrointestinal blood loss that compounds the deficiency. Prematurity contributes because premature infants are born with lower iron stores. The ice-chewing is pagophagia, a form of pica that is a specific and well-recognised feature of iron deficiency and resolves with iron replacement; families rarely volunteer it, so it must be asked for directly. ^[4][5]

Management. The definitive treatment is oral elemental iron at 3 to 6 mg per kg per day, given once daily or on alternate days, which absorbs better and causes fewer gastrointestinal side effects than traditional three-times-daily split dosing because it limits the post-dose hepcidin surge. Ferrous sulfate is the standard preparation and is roughly 20 percent elemental iron. Treatment continues for at least three months to rebuild the haemoglobin and replete the stores. The expected response is a reticulocyte rise within 7 to 10 days and a haemoglobin gain of about 10 g per litre per week, with a measurable rise by four weeks. Dietary advice accompanies the iron: cut the cow's milk to below 500 mL per day, introduce iron-rich solids, and avoid cow's milk before 12 months in future. ^[3][8]