Haemolytic anaemia is a condition where red blood cells are destroyed more quickly than the body can produce new ones. Red blood cells, responsible for carrying oxygen, normally live about 120 days. In haemolytic anaemia, their lifespan is shortened, leading to insufficient red blood cells and reduced oxygen delivery.
The Mechanism of Red Blood Cell Destruction
Red blood cell destruction in haemolytic anaemia can occur through two primary pathways: intravascular and extravascular hemolysis. Intravascular hemolysis breaks down red blood cells directly within the bloodstream, releasing hemoglobin into the plasma. This can be filtered by the kidneys, causing dark urine.
Extravascular hemolysis, more common, occurs outside blood vessels, mainly in the spleen, liver, and bone marrow. Macrophages, immune cells, remove damaged red blood cells. An enlarged spleen can also sequester healthy red blood cells, contributing to their destruction.
Identifying the Causes
Haemolytic anaemia has inherited and acquired causes. Inherited causes stem from genetic defects leading to red blood cell abnormalities. For example, conditions like G6PD deficiency, hereditary spherocytosis, hereditary elliptocytosis, and pyruvate kinase deficiency involve defects in red blood cell enzymes or membrane structure, making them fragile and prone to destruction.
Sickle cell disease and thalassemia are inherited conditions where genetic mutations affect hemoglobin production or structure. These abnormal red blood cells have a significantly reduced lifespan, often 10-20 days for sickle cells, leading to ongoing destruction.
Acquired causes develop later in life from external factors or the immune system. Autoimmune haemolytic anaemia (AIHA) is a common example, where the immune system mistakenly produces antibodies that attack red blood cells. Drug-induced haemolytic anaemia occurs when medications trigger an immune response or directly damage red blood cells.
Other acquired causes include mechanical damage (e.g., from artificial heart valves or hemodialysis), infections (e.g., malaria, babesiosis), exposure to toxins or chemicals, and an overactive spleen.
Recognizing the Symptoms
Symptoms of haemolytic anaemia result from reduced oxygen-carrying red blood cells and their breakdown products. Fatigue is common due to insufficient oxygen. Pallor, or pale skin, is another frequent sign, especially in mucous membranes.
Jaundice, a yellowing of the skin and eyes, occurs from bilirubin buildup, a pigment from red blood cell breakdown. Dark urine can also be a symptom, especially with intravascular hemolysis, as free hemoglobin is excreted. Other symptoms include shortness of breath, rapid heart rate (tachycardia), and an enlarged spleen or liver (splenomegaly or hepatomegaly). Symptom severity varies with the rate of red blood cell destruction and bone marrow compensation.
Diagnosis and Management
Diagnosis involves a physical examination and blood tests. A complete blood count (CBC) reveals a low red blood cell count. A reticulocyte count, measuring immature red blood cells, is often elevated as the bone marrow compensates. Levels of unconjugated bilirubin, lactate dehydrogenase (LDH), and haptoglobin are assessed; high bilirubin and LDH, and low haptoglobin, indicate increased red blood cell breakdown.
The direct antiglobulin test (Coombs test) determines if antibodies are attacking red blood cells, useful for diagnosing autoimmune haemolytic anaemia. A peripheral blood smear examines red blood cell size and shape for abnormalities. Further tests include hemoglobin electrophoresis for structure analysis and genetic tests for suspected inherited conditions.
Management focuses on treating the underlying cause and alleviating symptoms. For autoimmune causes, corticosteroids are often a first-line treatment to suppress the immune system and reduce red blood cell destruction. Immunosuppressants may also be used. Blood transfusions are administered for severe anaemia to quickly increase red blood cells and oxygen-carrying capacity.
If the spleen is overly active in destroying red blood cells, a splenectomy (surgical removal of the spleen) may be considered. Folic acid supplementation supports the bone marrow’s increased production of new red blood cells. If a medication is the cause, discontinuing it is a primary management step.