SN4 SHORT NOTE 5M ★ High-yield

Define anaemia. Classify it morphologically and aetiologically.

Physiology · 1st Professional — Pre-Clinical

Definition

Anaemia = a reduction in haemoglobin concentration, red cell count or packed cell volume below the normal for age and sex, leading to reduced oxygen-carrying capacity.

Morphological Classification

Type	MCV	MCHC	Examples
Microcytic hypochromic	< 80 fL	< 32%	Iron deficiency, thalassaemia, sideroblastic, chronic disease
Normocytic normochromic	80–100 fL	32–36%	Acute haemorrhage, haemolysis, chronic renal failure, aplastic
Macrocytic	> 100 fL	Normal	Vitamin B12 and folate deficiency, liver disease, hypothyroidism

Aetiological Classification

1. Blood loss — acute (trauma) or chronic (hookworm, menorrhagia, piles, peptic ulcer)

2. Impaired production

– Deficiency — iron, B12, folate, protein

– Marrow failure — aplastic anaemia, leukaemia, marrow infiltration

– ↓ Erythropoietin — chronic renal failure

3. Increased destruction (haemolytic)

– Intracorpuscular — membrane (spherocytosis), enzyme (G6PD), haemoglobin (thalassaemia, sickle cell)

– Extracorpuscular — autoimmune, malaria, incompatible transfusion, snake venom, drugs

Red Cell Indices

Index	Formula	Normal
MCV	PCV × 10 ÷ RBC count	80–100 fL
MCH	Hb × 10 ÷ RBC count	27–32 pg
MCHC	Hb × 100 ÷ PCV	32–36%

Clinical Features

Pallor, easy fatigue, exertional dyspnoea, palpitations
Tachycardia, wide pulse pressure, haemic murmur
Angina and cardiac failure in severe cases
Specific — koilonychia and glossitis in iron deficiency; subacute combined degeneration in B12 deficiency; jaundice in haemolysis

Applied Aspects

Iron deficiency is the commonest anaemia in India, especially in women and children; hookworm is a major cause
Always find the cause — iron deficiency in an adult male means occult GI blood loss until proved otherwise
Reticulocyte count distinguishes hypoproliferative (low) from haemolytic or post-haemorrhagic (high) anaemia

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