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]

SAQ 2 (10)

A 13-year-old girl presents with fatigue and pallor. She has heavy menstrual bleeding, a vegetarian diet, and no other medical history. Her haemoglobin is 84 g per litre with a mean cell volume of 70 fL. Her ferritin is 3 micrograms per litre. She is started on oral elemental iron at 5 mg per kg per day once daily. She returns at four weeks with no change in her haemoglobin. She reports she has been taking the iron daily. [1][4]

1. Outline the systematic approach to a refractory iron deficiency anaemia at four weeks of confirmed compliant therapy. (4) [1][3]
2. What specific tests should be sent in this girl to identify an underlying cause, and why? (3) [4][7]
3. Discuss the role of intravenous iron and the principles of transfusion in a child with iron deficiency anaemia. (3) [3][6]

Model answer

Refractory workup. A refractory iron deficiency anaemia — no haemoglobin rise at four weeks despite confirmed compliant oral iron at an appropriate dose — demands a structured search rather than more iron. The four questions are: is the adherence genuinely confirmed (here it is), is there ongoing blood loss, is there malabsorption, and is the diagnosis correct? Ongoing blood loss in this girl means quantifying the menorrhagia and looking for gastrointestinal loss. Malabsorption means coeliac disease, which is silent and common. The diagnosis should be re-confirmed — a normal ferritin with a high red cell count would point to thalassaemia trait, but her ferritin is genuinely low. Only after these are addressed is escalating treatment appropriate. [1][3]

Specific tests. Coeliac serology with a tissue transglutaminase IgA and a total IgA (to exclude IgA deficiency that would render the serology falsely negative) is essential, because coeliac disease is a common, silent and treatable cause of refractory iron deficiency. The heavy menstrual bleeding should be quantified and investigated, including a screen for bleeding disorders such as von Willebrand disease, which is common in adolescent menorrhagia. A faecal calprotectin screens for gut inflammation from inflammatory bowel disease. If these are unrevealing, referral for endoscopic evaluation of the gastrointestinal tract to look for a bleeding source such as a Meckel diverticulum, polyps or inflammatory bowel disease is the next step. In a child over three years or any boy this workup is mandatory, but it applies equally to an adolescent girl whose loss is not fully explained by menstruation. [4][7]

Intravenous iron and transfusion. Intravenous iron is reserved for the child who cannot tolerate or absorb oral iron, who has ongoing gut inflammation such as active inflammatory bowel disease, or who needs a rapid haemoglobin response before surgery. Modern preparations such as ferric carboxymaltose, ferric derisomaltose and iron polymaltose allow high single doses in children with a good safety profile, though a test dose and observation for hypersensitivity remain prudent and local protocols govern the choice. Transfusion is reserved for the child with severe symptomatic anaemia and cardiovascular compromise — tachycardia, a gallop, hepatomegaly or respiratory distress — and is given cautiously and slowly in small aliquots, because the hypoxic, anaemic myocardium is poorly tolerant of volume and at risk of pulmonary oedema. In the most severe cases an exchange transfusion raises the haemoglobin without the volume load. Transfusion is restrictive and clinical, never for a haemoglobin number alone. [3][6]