GPAtlas🧭 When to suspect
Suspect iron deficiency anaemia (IDA) – the commonest cause of a microcytic, hypochromic anaemia – in anyone presenting with fatigue, reduced exercise tolerance, or exertional breathlessness. It is defined by a low haemoglobin together with a low serum ferritin, with red cells that are typically microcytic (low mean cell volume, MCV) and hypochromic.
Raise suspicion where there is a plausible mechanism: dietary insufficiency, a source of blood loss (menorrhagia or gastrointestinal (GI) loss), malabsorption, or increased physiological demand such as pregnancy. Classic clinical signs – pallor, koilonychia, angular stomatitis – support the diagnosis but their absence does not exclude it.
The key caveat in primary care is that chronic, slow blood loss is often well tolerated: symptoms and signs may be entirely absent even at a very low haemoglobin, so the diagnosis is frequently made on bloods alone. The clinical priority is then twofold: confirm and treat the iron deficiency, and identify the underlying cause.
| Group | Haemoglobin threshold for anaemia |
|---|---|
| Men (over 15 years) | < 130 g/L |
| Non-pregnant women (over 15 years) and children 12–14 years | < 120 g/L |
| Pregnancy – first trimester | < 110 g/L |
| Pregnancy – second and third trimester | < 105 g/L |
| Postpartum | < 100 g/L |
|
⚠️ Common pitfall A normal MCV does not exclude iron deficiency. Microcytosis is a late feature, and a coexisting cause of macrocytosis (B12 or folate deficiency, alcohol, chronic disease) can pull the MCV back into range. If iron deficiency is plausible, check ferritin rather than waiting for the red cells to turn microcytic. |
Source: BSG · World Health Organization
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