Pathology
Microcytic Anaemia
Microcytic anaemia for MBBS and NEET-PG: iron deficiency metabolism, blood picture, iron studies, and differentiation from thalassaemia, chronic disease and sideroblastic anaemia, mapped to NMC codes PA14.1 to PA14.3.
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Microcytic Anaemia
Microcytic anaemia for MBBS and NEET-PG: iron deficiency metabolism, blood picture, iron studies, and differentiation from thalassaemia, chronic disease and sideroblastic anaemia, mapped to NMC codes PA14.1 to PA14.3.
This chapter focuses on the microcytic hypochromic anaemias, chiefly iron deficiency, and the way iron studies distinguish them. It covers iron metabolism, the causes, blood picture and investigations of iron deficiency, and the differentiation from thalassaemia, anaemia of chronic disease and sideroblastic anaemia.
High-yield: Microcytic Anaemia
- Iron deficiency anaemia is the most common cause of anaemia worldwide and the classic microcytic hypochromic anaemia.
- The blood film in iron deficiency shows small pale red cells with anisocytosis, poikilocytosis and pencil cells.
- In iron deficiency the serum ferritin is low, serum iron is low, total iron-binding capacity is high and transferrin saturation is low.
- Ferritin is the most useful single test of body iron stores and falls early in deficiency.
- Common causes of iron deficiency are chronic blood loss, poor dietary intake, malabsorption and increased demand in pregnancy.
- In an adult man or postmenopausal woman, occult gastrointestinal blood loss must be excluded as a cause of iron deficiency.
- Anaemia of chronic disease is usually normocytic but can become microcytic, with low serum iron, low total iron-binding capacity and normal or raised ferritin.
- Hepcidin, raised in chronic disease, blocks iron release from stores and reduces intestinal absorption.
- Thalassaemia produces microcytosis out of proportion to the degree of anaemia, with a normal or raised red cell count.
- Sideroblastic anaemia shows ring sideroblasts in the marrow, a dimorphic film and raised serum iron and ferritin.
- The Mentzer index (MCV divided by red cell count) helps distinguish iron deficiency (above 13) from thalassaemia trait (below 13).
- Koilonychia, glossitis and angular stomatitis are clinical signs of chronic iron deficiency.
- The treatment response to oral iron is confirmed by a reticulocyte rise within a week.
- Plummer-Vinson syndrome links iron deficiency anaemia with an oesophageal web and dysphagia.
Iron studies in microcytic anaemia
- **Iron deficiency:** Low ferritin, low serum iron, high TIBC, low transferrin saturation.
- **Chronic disease:** Low serum iron, low TIBC, normal or raised ferritin (raised hepcidin).
- **Thalassaemia:** Normal or raised iron and ferritin; microcytosis with normal or high red cell count.
- **Sideroblastic:** Raised iron and ferritin; ring sideroblasts in marrow; dimorphic film.
NMC competencies in this chapter
- **PA14.1:** Iron metabolism, aetiology, investigations and smear findings in iron deficiency anaemia
- **PA14.2:** Differentiate microcytic anaemias using iron studies and other investigations
- **PA14.3:** Describe the blood picture of iron deficiency anaemia
Frequently Asked Questions
What is the earliest change in iron deficiency?
A fall in serum ferritin, which reflects depletion of iron stores before the haemoglobin drops.
How do iron deficiency and thalassaemia differ on iron studies?
Iron deficiency shows low ferritin and low iron with a high iron-binding capacity, while thalassaemia has normal or raised iron and ferritin.
What is the blood picture in iron deficiency?
Microcytic hypochromic red cells with anisocytosis, poikilocytosis and pencil cells.
Why must occult blood loss be excluded in men with iron deficiency?
Because in adult men and postmenopausal women, gastrointestinal blood loss, including from cancer, is the leading cause and needs investigation.
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