Anaemia Classification
Direct answer
Anaemia is a haemoglobin concentration below the normal range for age and sex — by World Health Organization criteria, below 13 g/dL in adult men, 12 g/dL in non-pregnant women and 11 g/dL in pregnant women. It is classified morphologically, from red cell indices, into microcytic hypochromic, normocytic and macrocytic anaemias, and kinetically (by mechanism) into anaemias of decreased production, increased destruction (haemolysis) and blood loss. The morphological type, with the reticulocyte count and smear, directs further tests.
What you must remember
- Morphology by mean corpuscular volume: microcytic below 80 femtolitres, normocytic 80–100, macrocytic above 100; hypochromia means low mean corpuscular haemoglobin with widened central pallor.
- Microcytic hypochromic group: iron deficiency anaemia — the most common anaemia worldwide and in India — thalassaemia, sideroblastic anaemia, lead poisoning, and anaemia of chronic disease when microcytic.
- Separating the microcytoses: iron deficiency — low ferritin, raised iron-binding capacity; chronic disease — normal or high ferritin, low binding capacity; thalassaemia trait — normal ferritin, Mentzer index (MCV/red cell count) below 13, raised haemoglobin A2.
- Macrocytic group: megaloblastic — vitamin B12 deficiency (pernicious anaemia, vegetarian diets, ileal disease) and folate deficiency, with macro-ovalocytes and hypersegmented neutrophils; non-megaloblastic — alcohol, hypothyroidism, liver disease, myelodysplasia.
- Normocytic group: acute blood loss, haemolysis, aplastic anaemia, chronic kidney disease, and typical anaemia of chronic disease.
- Haemolysis markers: reticulocytosis, indirect hyperbilirubinaemia, raised lactate dehydrogenase, low haptoglobin; intravascular haemolysis adds haemoglobinaemia, haemoglobinuria and haemosiderinuria; the Coombs test detects immune haemolysis.
- Smear clues: pencil cells in iron deficiency; target cells in thalassaemia and liver disease; basophilic stippling in lead poisoning; spherocytes in hereditary spherocytosis; sickle cells; schistocytes in microangiopathic haemolysis.
Common confusion
The frequent error is calling every microcytic anaemia iron deficiency and giving iron without iron studies — useless in thalassaemia trait, which it also masks. Students forget that anaemia of chronic disease is typically normocytic and only later microcytic, and mistake treatment reticulocytosis (which raises the MCV) for a primary macrocytosis.
Exam-focused takeaway
In theory, write the definition with cut-offs, both classifications, and the approach — indices, reticulocyte count and smear, then targeted tests such as iron studies, B12 and folate, or Coombs test. In viva, classify a presented blood report in one sentence each for morphology and mechanism. In practicals, perform haemoglobin estimation and indices, count reticulocytes, and identify microcytic, macrocytic and haemolytic smears.
Practise MCQs and previous-year questions on anaemias and haemolysis in the PrepElephant app. Free notes continue on this website.
Frequently asked questions
What are the World Health Organization cut-offs for anaemia?
Below 13 g/dL in adult men, below 12 g/dL in non-pregnant women and below 11 g/dL in pregnant women; children have separate cut-offs.
What is the most common cause of anaemia in India?
Iron deficiency anaemia — inadequate dietary intake, chronic blood loss including hookworm, and increased demand in pregnancy and adolescence.
How is iron deficiency differentiated from thalassaemia trait?
Iron deficiency shows a high red cell distribution width, low ferritin and raised iron-binding capacity; thalassaemia trait shows a Mentzer index below 13 with normal or high ferritin and raised haemoglobin A2.
Which tests suggest haemolysis?
Reticulocytosis, indirect hyperbilirubinaemia, elevated lactate dehydrogenase and low haptoglobin; a positive direct Coombs test points to immune destruction.
Why is the reticulocyte count important?
It separates hypoproliferative anaemias (low or normal counts) from those with an appropriate marrow response (high counts — haemolysis, bleeding).
Is anaemia of chronic disease microcytic or normocytic?
Typically normocytic normochromic; it may turn microcytic when longstanding, and its normal or high ferritin distinguishes it from iron deficiency.
Practise this in the PrepElephant app
Question banks, previous-year questions, mock tests and revision tools — for Anaemia Classification and Pathology. Free to start.