Pathology
Introduction to Haematology
Introduction to haematology for MBBS and NEET-PG: haematopoiesis, anticoagulants, anaemia definition and classification, and the investigation of anaemia, mapped to NMC codes PA13.1 to PA13.5.
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Introduction to Haematology
Introduction to haematology for MBBS and NEET-PG: haematopoiesis, anticoagulants, anaemia definition and classification, and the investigation of anaemia, mapped to NMC codes PA13.1 to PA13.5.
This chapter lays the groundwork for haematology. It covers normal haematopoiesis and its sites, the anticoagulants used in blood collection, the definition and morphological classification of anaemia, and the laboratory investigations, including the blood count, film, iron studies and marrow examination.
High-yield: Introduction to Haematology
- Haematopoiesis in the adult occurs in the red bone marrow of the axial skeleton and the proximal ends of long bones.
- All blood cells arise from a common pluripotent haematopoietic stem cell.
- Erythropoietin, produced by the kidney, drives red cell production in response to hypoxia.
- Anaemia is defined as a reduction in haemoglobin below the reference range for age and sex.
- The morphological classification of anaemia uses the mean corpuscular volume to divide it into microcytic, normocytic and macrocytic types.
- Microcytic hypochromic anaemia is typified by iron deficiency and thalassaemia.
- Macrocytic anaemia is typified by vitamin B12 and folate deficiency.
- The reticulocyte count distinguishes anaemia due to reduced production (low count) from increased loss or destruction (high count).
- EDTA is the anticoagulant of choice for a complete blood count because it preserves cell morphology.
- Trisodium citrate is used for coagulation studies, and heparin for certain special tests and osmotic fragility.
- A peripheral blood smear allows assessment of red cell, white cell and platelet morphology.
- Iron studies include serum iron, total iron-binding capacity, transferrin saturation and ferritin.
- Bone marrow examination, by aspiration and trephine biopsy, is used to assess cellularity and infiltration.
- The normal adult haemoglobin range is roughly 13 to 17 g/dL in men and 12 to 15 g/dL in women.
- A blood film should be examined in the thin, well-spread tail where red cells lie in a single layer.
Morphological classification of anaemia
- **Microcytic (low MCV):** Iron deficiency, thalassaemia, anaemia of chronic disease, sideroblastic anaemia.
- **Normocytic (normal MCV):** Acute blood loss, haemolysis, chronic disease, marrow failure.
- **Macrocytic (high MCV):** Vitamin B12 and folate deficiency, liver disease, hypothyroidism.
- **Reticulocyte count:** Low in production defects; high in haemolysis or blood loss.
NMC competencies in this chapter
- **PA13.1:** Normal haematopoiesis, including sites and stages of development
- **PA13.2:** Role of anticoagulants in haematology specimen collection
- **PA13.3:** Definition and classification of anaemia by morphology and pathophysiology
- **PA13.4:** Investigation of anaemia: CBC, reticulocyte count, smear, iron studies, marrow
- **PA13.5:** Preparation, staining and examination of the peripheral blood smear
Frequently Asked Questions
How is anaemia classified morphologically?
By mean corpuscular volume into microcytic, normocytic and macrocytic types, which points towards likely causes such as iron deficiency or vitamin B12 deficiency.
Which anticoagulant is used for a complete blood count?
EDTA, because it preserves cell morphology; trisodium citrate is used for coagulation studies instead.
What does the reticulocyte count tell us?
It distinguishes anaemia from reduced marrow production, where the count is low, from anaemia due to haemolysis or blood loss, where the count is raised.
Where does haematopoiesis occur in adults?
In the red bone marrow of the axial skeleton and the proximal ends of the long bones, from a common pluripotent stem cell.
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