Anaemia
Low haemoglobin reducing oxygen delivery — most often from iron deficiency.
Overview
Anaemia is defined by haemoglobin below age- and sex-specific thresholds. Iron-deficiency anaemia is the commonest cause worldwide. The underlying cause (diet, bleeding, malabsorption) must be identified, not just the haemoglobin corrected.
Symptoms
- • Fatigue
- • Breathlessness on exertion
- • Pallor
- • Palpitations
- • Dizziness
- • Pica (craving non-food items)
Risk factors
- • Menstrual blood loss
- • Pregnancy
- • Vegetarian/vegan diet
- • GI conditions (coeliac, IBD)
- • Chronic kidney disease
Causes
- • Iron deficiency
- • B12 or folate deficiency
- • Chronic disease
- • Haemolysis
- • Bone marrow disorders
🚨 Red flags — seek urgent care
- • Chest pain or syncope with anaemia
- • Black or bloody stools
- • Heavy menstrual bleeding causing collapse
When to seek care
- • Persistent fatigue with pallor
- • Any visible bleeding
- • Symptoms during pregnancy
Diagnosis
- • Hb <130 g/L (men), <120 g/L (non-pregnant women), <110 g/L (pregnancy)
- • Classify by MCV: microcytic (iron deficiency, thalassaemia), normocytic (chronic disease, acute loss), macrocytic (B12/folate, hypothyroid)
- • Iron studies, B12, folate, reticulocyte count, blood film; ferritin <30 µg/L confirms iron deficiency
- • Investigate cause — endoscopy for unexplained iron deficiency in men or post-menopausal women
Treatment
- • Iron-deficiency: oral ferrous sulfate or alternate-day dosing for tolerance; IV iron for malabsorption or intolerance
- • B12 deficiency: hydroxocobalamin IM loading then maintenance (oral if dietary cause only)
- • Folate deficiency: oral folic acid 5 mg daily; ensure B12 not co-deficient first
- • Treat underlying cause (GI bleeding, menorrhagia, coeliac, chronic kidney disease)
- • Blood transfusion for symptomatic severe anaemia or acute haemorrhage
Prevention
- • Iron-rich diet, vitamin C with meals for absorption
- • Vegan/vegetarian B12 supplementation
- • Antenatal iron and folate as advised
- • Manage heavy menstrual bleeding
Complications
- • Cardiovascular strain (high-output failure, angina)
- • Cognitive impairment, fatigue, falls
- • Pregnancy complications (preterm birth, low birth weight)
- • Subacute combined cord degeneration (B12 deficiency)
Education & self-care
This guidance is reviewed by Dr. Handel Emery, MD, FRCP (UK) and last updated 2026-06-08. It is educational and not a substitute for professional medical advice.
Frequently asked questions
Why am I still tired on iron tablets?
It can take 2–3 months for haemoglobin to normalise and 6 months to fully replete iron stores. Persistent symptoms warrant rechecking.
What are the most common causes?
Iron deficiency is the leading cause worldwide, usually from blood loss (menstrual or gastrointestinal) or poor intake. Vitamin B12, folate deficiency, chronic disease and inherited haemoglobin disorders are also frequent.
How long until iron tablets work?
Haemoglobin typically rises by about 10 g/L every 2 weeks once iron is replaced. Most people are restored to normal within 2–3 months, but iron stores (ferritin) take longer to refill.
When are intravenous iron or transfusion needed?
IV iron is used when oral iron is not tolerated, not absorbed, or replacement is needed quickly. Transfusion is reserved for severe symptomatic anaemia or active bleeding.