Iron deficiency anaemia (IDA) is the most common nutritional deficiency worldwide and a frequent clinical condition encountered in both primary and secondary care. This article discusses the causes and risk factors for IDA, symptoms and diagnostic investigations, interpretation of iron studies, different types of anaemia, treatment strategies including oral and intravenous iron therapy, pharmacokinetics, adverse effects, and important drug interactions associated with iron supplementation. Iron Deficiency Anaemia Iron is a trace element essential for several cellular functions, including the activity of enzymes and proteins such as haemoglobin. Iron deficiency anaemia (IDA) is a reduction in the production of red blood cells (RBC) due to low iron stores in the body; iron is essential for the synthesis of new RBC (erythropoiesis) and particularly haemoglobin, which allows RBC to transport oxygen. Anaemia is defined as a low haemoglobin level. IDA is the most common cause of anaemia and the most common nutritional deficiency in the world, affecting 30% of the population. Women and children are more affected by IDA as they have increased requirements. Only 5-15% of dietary iron is absorbed. Daily requirements for iron are around 5mg for men and 15mg for women and children. The body can only absorb 10-20mg of iron per day. By TeachMeSeries Ltd (2026) Fig 1: Iron metabolism and recycling Risk Factors for IDA The following patient groups are at increased risk of developing IDA: Decreased Dietary Intake Elderly patients Vegan or vegetarian diets Restricted diets Poor nutritional intake Most dietary iron is derived from meat sources. Decreased Absorption Gastrointestinal resection Coeliac disease Inflammatory bowel disease Use of chelating drugs such as tetracyclines and quinolones Increased Blood Loss Gastrointestinal bleeding Menstruation Malignancy Increased Utilisation Pregnancy (2–10-fold increased requirements) Chronic Disease States Congestive cardiac failure Chronic kidney disease (CKD) Due to factors such as poor nutrition, antiplatelet or anticoagulant therapy Symptoms of IDA Symptoms of IDA are largely caused by reduced oxygen delivery to tissues and include: Shortness of breath Fatigue Palpitations Tachycardia Angina Headache Pallor Diagnosis Full Blood Count (FBC) Diagnosis of IDA requires blood testing, including a full blood count (FBC). In IDA, the FBC typically demonstrates: Low haemoglobin (Hb) Low mean corpuscular volume (MCV) IDA is a microcytic, hypochromic anaemia, meaning the red blood cells are smaller and paler than normal. Haemoglobin Anaemia can be diagnosed using the following haemoglobin thresholds (NICE, WHO): Patient group Haemoglobin level Men > 15 years age <130g/L Women > 15 years age <120g/L Children 12-14 years of age <120g/L Pregnancy 1st trimester <110g/L Pregnancy 2nd and 3rd trimester <105g/L Postpartum <100g/L Iron Studies Iron studies help differentiate IDA from other causes of microcytic anaemia. Ferritin Ferritin is the storage molecule for iron. In isolated iron deficiency, haemoglobin may remain normal initially and a ferritin level of <30ug/l confirms a diagnosis of IDA. Ferritin may be normal or raised in other anaemias such as: Anaemia of chronic disease Haemolytic anaemia Bone marrow disorders Iron supplementation is not indicated in anaemia other than those due to iron deficiency. Ferritin levels are raised in the presence of inflammation, therefore c-reactive protein (CRP) should be taken alongside ferritin levels. Furthermore, ferritin levels may be less reliable in pregnancy. In the presence of inflammation (CRP >20mg/L), a ferritin level of <100ug/L is indicative of IDA. Transferrin, TIBC and Serum Iron Transferrin transports iron around the body. In IDA: Serum iron is low Transferrin saturation is low Total iron-binding capacity (TIBC) is raised Vitamin B12 and Folate Testing B12 and folate should also be checked if Normocytic anaemia with low/normal ferritin Poor response to iron supplements B12 deficiency suspected i.e. malnourished, malabsorption, lack of folate supplements in pregnancy Elderly A combined iron and B12/folate deficiency may present as microcytic anaemia. Other Types of Anaemia Normocytic Anaemia Normocytic anaemia occurs when RBC are normal in size but insufficient in number, causes include: Chronic kidney disease Chronic inflammatory disease HIV infection MCV remains within the normal range Macrocytic Anaemia Macrocytic anaemia occurs when RBC are large, and MCV will be raised. An important example is megaloblastic anaemia (anaemia caused by impaired DNA synthesis) caused by: Vitamin B12 deficiency Folate deficiency Treatment of IDA Patients diagnosed with IDA should receive iron supplementation to restore haemoglobin levels and replenish iron stores. First-line treatment consists of oral ferrous iron salts, with ferrous sulfate most commonly prescribed. Oral Iron Therapy Once daily administration of ferrous salts is recommended, reducing to every other day administration if the patient experiences adverse effects. Treatment should be continued for 3 months after the haemoglobin returns within range, and haemoglobin levels should be checked after 2-4 weeks to assess response. After starting iron supplementation, haemoglobin should be expected to rise by 20g/L per month. Iron salts are not bioequivalent, the content of ferrous iron is described below: By TeachMeSeries Ltd (2026) Fig 2: Iron Content of Oral Iron Salts Intravenous Iron Therapy For intravenous iron supplementation, haemoglobin should be re-assessed no earlier than 4 weeks after completion of treatment. Intravenous iron may be advantageous in: Severe IDA Malabsorption Non-functional or inaccessible gastrointestinal tract Need for rapid correction Chronic kidney disease patients requiring regular replacement Malignancies Pharmacokinetics Oral Iron Oral iron is absorbed primarily in the duodenum and proximal jejunum, however they demonstrate poor bioavailability. Ferrous salts are absorbed most effectively, with absorption increasing in iron deficiency and on an empty stomach, however incidence of side effects may be higher with the latter. After absorption, iron is bound to transferrin and transported to bone marrow and incorporated into haemoglobin, or stored within ferritin. Both dietary and oral iron salts are excreted through loss of cells in urine, faeces, hair, skin, nails and via blood loss. Intravenous Iron Common intravenous preparations include: Ferric derisomaltose (Monofer®, Diafer®) Ferric carboxymaltose (Ferinject®) These formulations contain iron complexes providing a slow release of bioavailable iron to iron transport (transferrin) and storage (ferritin) proteins. Therapeutic response can be seen within a few days, and ferritin will peak within a few days then slowly return to baseline after weeks. Adverse Effects Oral Iron Oral iron salts are renowned for causing gastrointestinal side effects such as constipation, diarrhoea and nausea. Taking iron salts with food can reduce gastrointestinal side effects. Patients should be counselled not to suck or chew oral iron supplements as this may cause mouth ulceration and tooth discolouration. Furthermore, oral iron may turn patients stools black and sticky, and patients should be informed of this prior to starting treatment. For this reason, oral iron should be withheld 7 days prior to endoscopy to avoid interference with visualising the colon Intravenous Iron Intravenous iron is less likely to cause gastrointestinal side effects but may cause: Iron tattooing from paravenous leakage Hypophosphataemia Anaphylactic reactions Patients should be counselled regarding the risk of permanent brown skin discolouration before treatment. Parenteral iron should also be used cautiously in patients with acute or chronic infection because iron may promote microbial growth. Interactions Iron binds to drugs such as levothyroxine, quinolones and bisphosphonates, reducing their absorption. Other drugs and food sources bind to iron, reducing its absorption, including cholestyramine, antacids, zinc, calcium, tea, coffee, milk, eggs and wholegrains; iron should generally be taken 1 hour before or 2 hours after these products. Tetracycline forms an insoluble iron complex, leading to reduced absorption of both agents. If a patient requires intravenous iron, and still needs oral iron supplementation after this, treatment with oral iron should be held for 2 weeks after IV administration, as oral absorption of iron will be reduced if administered concomitantly. References Anaemia, iron deficiency | Treatment summaries | BNF | NICE Accessed 3/5/26 Anaemia – iron deficiency | Health topics A to Z | CKS | NICE Accessed 7/5/26 Kumar A, et al. BMJ Open Gastro 2022;9:e000759. doi:10.1136/bmjgast-2021-000759 Ritter JM, Flower RJ, Henderson G, Loke YK, MacEwan DJ. Rang & Dale’s Pharmacology. 9th ed. London: Elsevier; 2019. Hitchings BSc, M., Lonsdale, D., Burrage, D., Baker, E. (2022). The Top 100 Drugs – E-Book. Netherlands: Elsevier. Ferrous Sulfate Tablets 200mg – Summary of Product Characteristics (SmPC) – (emc) | 4231 Accessed 10/5/26 Ferrous fumarate 210mg Tablets – Summary of Product Characteristics (SmPC) – (emc) | 2821 Accessed 10/5/26 Monofer 100mg/ml solution for injection/infusion – Summary of Product Characteristics (SmPC) – (emc) | 5676 Accessed 10/5/26 Ferinject 50 mg iron/mL dispersion for injection/infusion. – Summary of Product Characteristics (SmPC) – (emc) | 5910 Accessed 10/5/26 Do you think you’re ready? Take the quiz below Pro Feature - Quiz Iron Deficiency Anaemia Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 More Questions Available Upgrade to TeachMePharmacy Pro Challenge yourself with over 200 multiple-choice questions to reinforce learning. Learn More Rate This Article