Iron Deficiency Anaemia

Iron deficiency anaemia (IDA) is characterized by a reduction in red cell indices (MCV <80fL) due to inadequate iron for haemoglobin synthesis. In the UK, IDA affects approximately 2-5% of adult men and post-menopausal women, but up to 10% of menstruating women. The primary concern in non-menstruating patients is occult malignancy, specifically colorectal cancer. Iron is absorbed in its ferrous (Fe2+) form in the duodenum and proximal jejunum, a process regulated by the hormone hepcidin. A normal diet contains 10-15mg of iron daily, of which only 1-2mg is absorbed. When demand exceeds intake or blood loss occurs, iron stores (ferritin) are exhausted first, followed by a drop in serum iron and an increase in total iron-binding capacity (TIBC), eventually leading to a reduction in haemoglobin. Patients typically present with non-specific symptoms of fatigue and dyspnoea, but physical signs such as koilonychia and glossitis may be present in severe chronic cases. NICE guidelines emphasize the 2-week wait referral for suspected gastrointestinal cancer in patients over 60 with IDA or those over 50 with unexplained rectal bleeding and IDA.

Iron is essential for the production of haemoglobin, myoglobin, and several enzyme systems. Total body iron is approximately 3-4g, with two-thirds found in haemoglobin. Absorption occurs via divalent metal transporter 1 (DMT1) on duodenal enterocytes. Once inside the cell, iron is either stored as ferritin or transported into the plasma via ferroportin. Ferroportin activity is inhibited by hepcidin, which is produced by the liver in response to high iron levels or inflammation. This explains why chronic inflammation leads to 'anaemia of chronic disease' where iron is trapped in stores. Aetiology of IDA includes: 1) Increased demand (pregnancy, rapid growth), 2) Chronic blood loss (menorrhagia, GI bleeding, hookworm in developing nations), 3) Malabsorption (Coeliac disease, post-gastrectomy), and 4) Dietary deficiency (common in vegan diets or poverty). Pathophysiologically, the absence of iron prevents the final step of haem synthesis (insertion of Fe into protoporphyrin IX), leading to small, pale red blood cells.

Presenting symptoms are frequently non-specific: tiredness, lethargy, exertional dyspnoea, and palpitations. More specific manifestations of chronic deficiency include pica (craving non-food items), atrophic glossitis (smooth tongue), angular cheilitis (cracks at mouth corners), and koilonychia (spoon-shaped nails). Severe cases may lead to high-output heart failure. In children, IDA is associated with cognitive and behavioural impairments. Diagnostic red flags for UK practice center on gastrointestinal malignancy; any male or post-menopausal female with iron deficiency (low ferritin) without an obvious cause should undergo gastroscopy and colonoscopy. Furthermore, patients may present with the Plummer-Vinson syndrome (triad of IDA, oesophageal webs, and glossitis). Failure to respond to oral iron should prompt investigation into compliance, ongoing bleeding, or co-existing conditions like Coeliac disease or H. pylori infection which impairs absorption.

Bedside: Urine dipstick (haematuria as a cause of blood loss). Bloods: Full Blood Count (low Hb, low MCV/MCH, high RDW), Blood Film (hypochromic microcytic cells, pencil cells), Serum Ferritin (Low <15-30μg/L is diagnostic; note: ferritin can be raised in infection/inflammation), Serum Iron, TIBC (High), and Transferrin Saturation (<15%). Special Tests: Coeliac serology (anti-TTG) is mandatory in all adults. Imaging: Upper GI endoscopy (OGD) and Colonoscopy (or CT Colonography if unfit) to exclude malignancy as per NICE NG12. H. pylori stool antigen if refractory to treatment.

Conservative: Dietary advice focusing on iron-rich foods (red meat, dark green leafy vegetables, lentils). Medical: Oral iron supplementation is first-line. Common preparations include Ferrous Fumarate (210mg BD/TDS) or Ferrous Sulfate (200mg BD/TDS). Recent evidence suggests alternate-day dosing may improve absorption and reduce side effects (nausea, abdominal pain, constipation, black stools). Treatment should continue for 3 months after Hb normalization to replenish stores. Intravenous iron (e.g., Ferric Carboxymaltose) is indicated if oral iron is not tolerated, in severe malabsorption (e.g., IBD), or if rapid correction is required (pre-operatively). Surgical: Address the underlying cause (e.g., resection of GI malignancy, management of uterine fibroids).