31st July 2023

Anaemia

Iron Deficiency Anaemia

Anaemia is not a disease in its own right, and an underlying cause should always be sought. Further information regarding anaemia more generally can be found in the ‘Haematology’ section.

Patients may have clinical features of anaemia in general, such as fatigue, dyspnoea, pallor and tachycardia. Those with chronic iron deficiency may develop atrophic glossitis, angular stomatitis and/or koilonychia.

Iron deficiency is the most common cause of anaemia, and patients will have a microcytosis along with their low haemoglobin levels. MCV, MCH and MCHC are all reduced. The exception is when patients have coexistent folate and/or B12 deficiency, as this will lead to a dimorphic red cell population with both microcytes and macrocytes circulating. In these instances, the red cell distribution width (RCDW) would be high.

The differential for a microcytic anaemia includes thalassaemia, sideroblastic anaemia and lead poisoning. These can be distinguished from iron deficiency anaemia with haematinics (serum ferritin, iron and transferrin saturation) and a blood film. The film in iron deficiency anaemia reveals hypochromic, microcytic cells, and there may also be target cells and pencil poikilocytes.

Patients with chronic bleeding typically present with iron deficiency anaemia, and as such, 1 in 6 menstruating women have the condition. New onset iron deficiency anaemia in all men, and all women after the menopause, should be assumed to be from a GI tract lesion until proven otherwise, unless they have overt non-gastrointestinal bleeding. Other causes include malabsorption (e.g., coeliac disease), dietary deficiency and hookworm infection.

NICE guidelines state that all men and postmenopausal women with iron deficiency anaemia should be referred to gastroenterology, where they will undergo both upper and lower GI endoscopy. A coeliac screen should also be sent. If patients are over 60, or over 50 and have rectal bleeding, the referral should be under a 2-week wait pathway. Premenopausal women may also be referred to the gastroenterology team if they have bowel symptoms, a strong family history of GI malignancy or resistant disease.

If the above investigations do not reveal pathology and a cause is yet to be found, the small bowel should be imaged if the anaemia is transfusion dependent (otherwise, the diagnostic yield is very low). This can be done with video capsule endoscopy. Finally, angiography of the coeliac and mesenteric vessels may be required.

Along with managing the underlying cause, the iron deficiency itself can be treated with iron supplementation. Oral iron is adequate for most patients, e.g., ferrous sulphate or ferrous fumarate. This should be continued until haemoglobin returns to normal range, and for at least 3 months after this to allow stores to be replenished. Intravenous iron is required in a small proportion, such as those with chronic kidney disease. These patients should be iron replete prior to a trial of erythropoiesis stimulating agents.

The most common reason that patients fail to respond to iron replacement is compliance. Side effects include constipation and GI irritation; advise that these typically settle down with time. Troublesome adverse effects can be minimised if iron supplements are taken with or after food, or if dose frequency is reduced to alternate days.

Monitoring is important, and haemoglobin levels should be rechecked within 4 weeks of commencing iron supplementation, and periodically after this.

Algorithm for the management of iron deficiency anaemia, as suggested by the British Society of Gastroenterology. IDA is iron deficiency anaemia; IRT is iron replacement therapy; OGD is oesophago-gastroduodenoscopy.

Pernicious Anaemia

Describes autoimmune destruction of gastric parietal cells that secrete intrinsic factor, reducing vitamin B12 absorption. B12 is key in the erythropoiesis and in myelination of neurons, leading to the clinical features. Pernicious anaemia is the most common cause of B12 deficiency; the differential includes dietary deficiency (especially seen in vegans), disease of the terminal ileum (e.g., Crohn’s disease) or previous gastrectomy.

Pernicious anaemia is strongly associated with other autoimmune conditions; thus, a thorough past medical history and family history is required. The associations, clinical features and investigations are summarised in Table 1. The condition is rare in those <40 years old. Diagnosis is usually made with positive autoantibodies following clinical suspicion.

Table 1: Associations, clinical features and investigations for pernicious anaemia.

Management involves B12 replacement in the form of intramuscular hydroxocobalamin. If there are no neurological features, 3 injections per week are given for the first 2 weeks, followed by injections once every 3 months. The 1mg doses are given more frequently if neurological features are present; contact the haematology team for an appropriate regimen.

Schematic showing normal absorption of vitamin B12 from the diet. In pernicious anaemia, there is reduced or absent intrinsic factor secretion; therefore, much less vitamin B12 is absorbed at the terminal ileum.