Approach to Anaemia in Children
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Direct answer
Anaemia in children is evaluated first by the mean corpuscular volume, which sorts cases into microcytic, normocytic and macrocytic groups, then by the reticulocyte count, which shows marrow response. Iron deficiency is the commonest cause globally and is confirmed by low serum ferritin. Thalassaemia trait is suspected when microcytosis is out of proportion to the anaemia, such as a Mentzer index below 13 (MCV divided by red cell count).
What you must remember
- Age-specific threshold: WHO cut-offs are about 11 g/dL under five years and 11.5 g/dL for five to eleven years, so haemoglobin must be read against age.
- Microcytic group: MCV below the age-adjusted normal; causes include iron deficiency, thalassaemia trait, anaemia of chronic inflammation and lead poisoning.
- Iron deficiency: low ferritin, low serum iron, high total iron binding capacity and high RDW; ferritin is the most useful single test, though inflammation raises it.
- Thalassaemia trait: microcytosis with a normal or raised red cell count, normal ferritin, and raised HbA2 on haemoglobin electrophoresis in beta trait.
- Reticulocyte count: a low count means a hypoproliferative marrow, while a high count means a regenerative response to haemorrhage or haemolysis.
- Haemolysis clues: raised indirect bilirubin and LDH, abnormal red cell morphology on smear, and a positive direct Coombs test in autoimmune haemolysis.
A stepwise algorithm from pattern to proof
Work-up moves from a complete blood count to a specific test, and each step narrows the list of causes. Stop at the first step that explains the picture.
- Confirm and grade: check haemoglobin against age-specific cut-offs and record severity, since moderate or severe anaemia changes urgency.
- Classify by MCV: divide cases into microcytic, normocytic and macrocytic groups, using the age-adjusted limit for microcytosis.
- Add reticulocytes and smear: a low count points to marrow failure or early deficiency; a high count points to blood loss or haemolysis.
- Test the likely group: ferritin and iron studies for microcytosis; electrophoresis for thalassaemia; bilirubin, LDH and direct Coombs for haemolysis; vitamin B12, folate and thyroid tests for macrocytosis.
- Look for blood loss: check stool for occult blood and screen for hookworm, since chronic loss is a common cause of iron deficiency in older children.
- Escalate when unexplained: marrow examination for persistent cytopenias, and referral when more than one cell line is affected.
Where the exam tries to catch you
Anaemia questions reward the habit of testing before treating.
- Trap: diagnosing iron deficiency from haemoglobin alone Correct: low MCV, low ferritin and high TIBC are needed, because thalassaemia and chronic disease also cause anaemia.
- Trap: starting iron empirically for microcytosis Correct: iron-treated thalassaemia trait stays anaemic, so check ferritin and the Mentzer index first.
- Trap: calling a high reticulocyte count iron deficiency Correct: regeneration points to blood loss or haemolysis, whereas iron deficiency is hypoproliferative.
- Trap: attributing macrocytosis to folate deficiency only Correct: check vitamin B12, anticonvulsants, liver disease and hypothyroidism as well.
Frequently asked questions
What is the Mentzer index and how is it used?
The Mentzer index is the MCV divided by the red blood cell count, and values below 13 suggest thalassaemia trait rather than iron deficiency. It is a cheap screen that supports, but never replaces, haemoglobin electrophoresis.
Which test best confirms iron deficiency anaemia in children?
Serum ferritin is the most useful single test for iron deficiency anaemia in children, since it falls before anaemia develops. Ferritin can be normal or raised in inflammation, so a raised C-reactive protein weakens its interpretation.
What reticulocyte pattern suggests haemolysis?
Haemolysis produces a raised reticulocyte count, often with raised indirect bilirubin and LDH and abnormal red cell forms on smear. A positive direct Coombs test points to autoimmune haemolysis.
Why is a low reticulocyte count significant in anaemia?
A low reticulocyte count means the marrow is not responding, which suggests aplastic anaemia, early iron deficiency or chronic disease. It should prompt review of the other cell lines and a smear for blasts or abnormal cells.
When should a child with anaemia be referred to a haematologist?
Referral is needed for severe or unexplained anaemia, multi-lineage cytopenias, abnormal cells on smear, or a haemolytic picture without a clear cause. Early referral also applies when transfusion dependence or a family history of inherited anaemia is present.