GPAtlas🧭 When to suspect
Anaemia is not a diagnosis – it is a sign that something else is wrong, and the central task in primary care is to find and treat the underlying cause rather than simply hand out iron. It presents with non-specific symptoms such as fatigue, pallor, breathlessness on exertion, headache, tinnitus, and dizziness; when severe or rapid in onset it can cause tachycardia, angina, syncope, or overt haemodynamic compromise. Occasionally the cause declares itself on examination – for example koilonychia in long-standing iron deficiency.
In adults, anaemia is defined as a haemoglobin below 130 g/L in men, below 120 g/L in non-pregnant women, and below 110 g/L in the first trimester of pregnancy. The most useful first step in working out the cause is the mean cell volume (MCV), which sorts anaemia into three patterns and points you straight at the likely mechanism. Pair the MCV with the ferritin and you have answered most of the diagnostic question before any specialist is involved.
| Red cell size (MCV) | Pattern | Common causes to consider |
|---|---|---|
| < 80 fL | Microcytic | Iron deficiency (commonest), thalassaemia trait, anaemia of chronic disease, sideroblastic anaemia |
| 80–100 fL | Normocytic | Acute blood loss, anaemia of chronic disease, CKD, mixed haematinic deficiency, haemolysis, early marrow failure |
| > 100 fL | Macrocytic | B12 or folate deficiency, alcohol excess, liver disease, hypothyroidism, myelodysplasia, certain drugs |
The two clinical skills that matter are therefore: characterise the anaemia (MCV plus ferritin) to find the cause, and never miss the red flags – pancytopenia, haemodynamic compromise, neurological signs of B12 deficiency, and features pointing to gastrointestinal or haematological malignancy.
Source: BSG · NICE NG239
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