Iron Deficiency Anaemia

What Is Anaemia?

Anaemia means your blood does not have enough haemoglobin — the protein in red blood cells that carries oxygen around your body. The World Health Organization defines anaemia as:

• Haemoglobin below 130 g/L in adult men
• Haemoglobin below 120 g/L in non-pregnant adult women
• Haemoglobin below 110 g/L in pregnant women

Anaemia is not a diagnosis in itself — it is a sign that something is going on underneath. There are many possible causes, and iron deficiency is the most common worldwide. Other causes include vitamin B12 or folate deficiency, anaemia of chronic disease (linked to ongoing inflammation or illness), thalassaemia (a genetic condition affecting red blood cells), and others. Getting the cause right is important because the treatments are completely different.

Iron deficiency anaemia (IDA) is anaemia caused specifically by your iron stores being too depleted to make healthy red blood cells. It is the final stage of a progressive process — first your stored iron falls, then your red cell production becomes abnormal, and eventually your haemoglobin drops low enough to cause symptoms.

Symptoms of Iron Deficiency Anaemia

How you feel depends on how low your iron has dropped and how quickly it happened. Anaemia that develops slowly is often surprisingly well tolerated — your body adapts gradually. Rapid blood loss tends to feel much worse. Common symptoms include:

• Fatigue and tiredness — the most common symptom, and one that is often brushed off as "just stress" or "getting older"
• Pallor — paleness of the skin, the inside of the lower eyelid, and the nail beds
• Breathlessness on exertion — getting short of breath with activities that previously did not bother you
• Palpitations — noticing your heart racing or beating irregularly as it works harder to compensate
• Poor concentration and brain fog — iron is important for how the brain functions, so low levels can genuinely affect thinking and focus
• Headaches
• Restless legs syndrome — an uncomfortable urge to move your legs, especially at night; this is strongly linked to iron deficiency
• Pica — craving non-food items, most commonly ice but sometimes dirt or starch; this is a well-recognised sign of iron deficiency
• Spoon-shaped nails (koilonychia) — nails that curve inward rather than outward; a sign of longstanding iron deficiency
• Cracking at the corners of the mouth (angular cheilitis)
• A smooth, sore tongue (glossitis)
• Hair thinning — a generalised shedding rather than patchy hair loss

Some people — particularly older adults — can have surprisingly few symptoms even when their haemoglobin is quite low, simply because it has fallen so gradually that the body has adapted. A blood test is the only reliable way to know.

How Severe Is Iron Deficiency Anaemia?

Anaemia is broadly grouped by how low the haemoglobin has dropped:

• Mild anaemia — haemoglobin 100–129 g/L (men) / 100–119 g/L (women): often no symptoms or only mild tiredness
• Moderate anaemia — haemoglobin 70–99 g/L: clearly symptomatic; significant fatigue and breathlessness with activity
• Severe anaemia — haemoglobin below 70 g/L: places real stress on the heart and other organs; may need urgent treatment including a blood transfusion

How severe your anaemia is helps determine how urgently you need treatment — but no matter how mild or severe, the underlying cause still needs to be found.

How Is Iron Deficiency Anaemia Diagnosed?

Diagnosis is made through blood tests. Your doctor will look at two main sets of results:

Full blood examination (FBE)

This shows whether your haemoglobin is low, and what your red blood cells look like. In iron deficiency anaemia, the cells are typically smaller than normal (microcytosis) and paler (hypochromia) — both signs that your body does not have enough iron to make healthy red cells. The results also show whether your red cell sizes vary a lot (which they do in iron deficiency) and whether your platelet count is elevated (a common reaction to iron deficiency).

Iron studies

• Ferritin — your iron store level; low in iron deficiency (typically below 30, often below 15 µg/L)
• Serum iron — the iron currently circulating in your blood; low
• Total iron-binding capacity (TIBC) — how much iron your blood proteins could carry; elevated in iron deficiency because the body is reaching for more iron
• Transferrin saturation — how full those carriers are; low in iron deficiency (typically below 16%)

This pattern of results separates iron deficiency from other types of anaemia that can look similar on a blood count.

How the Cause Is Investigated

Finding out why your iron is low is just as important as treating the iron deficiency itself. Here is how that process typically works:

Treatment Options

Iron tablets

Iron tablets (usually ferrous sulphate or ferrous gluconate) are the standard first treatment when your gut can absorb iron normally and you can tolerate them. Taking iron with a glass of orange juice (vitamin C) improves absorption. Iron is best absorbed on an empty stomach, and away from other medications — particularly calcium tablets, antacids, and heartburn medications (PPIs).

Side effects are common and include constipation, nausea, stomach cramps, and very dark or black stools. If side effects are a problem, it can help to take iron with food (this reduces absorption a little but improves comfort), use a lower-dose tablet, or take it every second day rather than daily. The dark stools are expected and harmless — do not be alarmed.

Your haemoglobin should start rising within 2–4 weeks, and usually reaches a normal level within 2–3 months. But here is the important part: you should keep taking iron for at least 3–6 months after your haemoglobin normalises, to rebuild your iron stores. Stopping too early is the most common reason people's anaemia comes back.

Intravenous iron infusion

An IV iron infusion delivers iron directly into your bloodstream, bypassing the gut entirely. It is used when tablets cause intolerable side effects, when your gut cannot absorb iron properly (for example, after certain weight-loss operations or with coeliac disease), or when your iron needs to be restored quickly — before surgery, or in pregnancy with severe anaemia. For people who are also having a colonoscopy or gastroscopy to investigate their iron deficiency, Mr Nguyen will often arrange an iron infusion on the same day as the procedure if it is clinically appropriate — saving you a separate admission. See our article on iron infusions for more detail.

Blood transfusion

A blood transfusion is reserved for severe symptomatic anaemia (typically a haemoglobin below 70–80 g/L) or when urgent correction is needed — for example, if your heart is under strain from the anaemia or if you need surgery very soon. A transfusion corrects anaemia quickly, but it does not build up your iron stores, and it carries a small risk of reactions. It is used when the situation is urgent rather than as a routine treatment.

Iron Deficiency Anaemia and Bowel Cancer

Iron deficiency anaemia is one of the most common ways bowel cancer first comes to attention. Tumours in the colon — particularly in the right side — tend to bleed slowly and intermittently. Because the bleeding mixes with waste material deep inside the bowel, you usually cannot see it. Over months or years, this hidden blood loss quietly depletes your iron stores until anaemia eventually develops. By the time a blood test picks up the anaemia, the cancer may have been present for a long time without any other symptoms at all.

This is why unexplained iron deficiency anaemia in a man or postmenopausal woman is taken seriously and investigated with a colonoscopy — without exception. Right-sided colon cancers in particular often cause nothing except anaemia. There may be no change in bowel habit, no visible bleeding, no pain.

The genuinely reassuring news is that finding bowel cancer early — even through an anaemia investigation — makes a real difference to outcomes. When caught at an early stage, the five-year survival rate exceeds 90%. Investigating your iron deficiency anaemia properly is not just important — in some cases, it saves lives.

Frequently Asked Questions