What is iron deficiency anaemia?
Iron deficiency anaemia (IDA) occurs when there is not enough iron in the body to produce adequate haemoglobin. Iron is essential for haemoglobin synthesis in red blood cells. Without it, red cells become small (microcytic) and pale (hypochromic) and carry less oxygen. IDA is the most common cause of anaemia worldwide and the most common nutritional deficiency. It develops in stages: first iron stores (ferritin) deplete, then transport iron (serum iron) falls, then finally haemoglobin falls and anaemia develops.
Iron deficiency blood test results
| Test | Normal Range | Iron Deficiency Pattern |
|---|---|---|
| Haemoglobin (men) | 13.5–17.5 g/dL | Low (anaemia) |
| Haemoglobin (women) | 12.0–15.5 g/dL | Low (anaemia) |
| Ferritin | Men: 24–336 ng/mL; Women: 11–307 ng/mL | LOW (<30 ng/mL suggests deficiency) |
| Serum Iron | 60–170 mcg/dL | Low |
| TIBC | 250–370 mcg/dL | High (body makes more transferrin to scavenge iron) |
| Transferrin Saturation | 20–50% | Low (<16% = iron deficiency) |
| MCV (mean cell volume) | 80–100 fL | Low <80 fL (microcytic) |
Causes of iron deficiency
Blood loss (most important cause)
Gastrointestinal bleeding is the most common cause in men and postmenopausal women: peptic ulcer, gastritis, colorectal cancer, colon polyps, inflammatory bowel disease, coeliac disease, hookworm. Heavy menstrual periods (menorrhagia) is the most common cause in premenopausal women. Regular blood donation, surgical blood loss and haematuria (blood in urine) are other sources.
Inadequate intake or absorption
Vegetarian/vegan diets (plant iron is less well absorbed than haem iron from meat), pregnancy and infancy (high demand), coeliac disease and Crohn's disease (malabsorption), gastric bypass surgery, long-term PPI use (reduces stomach acid needed for iron absorption).
Why is ferritin the first test to fall?
Ferritin is the iron storage protein — it is the body's iron reserve. When dietary iron or absorption is inadequate, the body first draws on these reserves. Ferritin falls BEFORE haemoglobin, serum iron, or MCV changes. This is why ferritin is the earliest and most sensitive marker of iron deficiency, detectable weeks to months before anaemia develops. A low ferritin even with normal haemoglobin still warrants investigation and treatment.
Treatment of iron deficiency
| Treatment | When used | Notes |
|---|---|---|
| Oral iron (ferrous sulfate, ferrous gluconate) | Mild–moderate deficiency | Take on empty stomach if tolerated; vitamin C improves absorption; can cause GI side effects |
| IV iron infusion (ferric carboxymaltose, iron sucrose) | Severe deficiency, malabsorption, intolerance to oral | Single infusion replenishes stores rapidly |
| Dietary iron | Alongside supplements | Red meat, liver, dark leafy greens, lentils, fortified cereals |
Crucially: always find and treat the CAUSE of iron deficiency. In men and postmenopausal women, unexplained IDA should prompt investigation for GI bleeding — a colonoscopy and upper GI endoscopy are usually arranged.
Questions to ask your doctor
- Why am I iron deficient — is there a source of blood loss?
- Do I need an endoscopy?
- Should I take oral iron or IV iron?
- How long before I feel better?
- What foods will help my iron levels?