Warm autoimmune haemolytic anaemia is a rare disorder where the body’s own immune system turns against itself, mistakenly attacking healthy red blood cells at normal body temperature, leading to their premature destruction and a potentially life-threatening form of anaemia.
Understanding Warm Autoimmune Haemolytic Anaemia
Warm autoimmune haemolytic anaemia, often abbreviated as wAIHA, represents the most common form of autoimmune haemolytic anaemia. This condition occurs when the immune system produces autoantibodies, which are harmful antibodies that mistakenly target the body’s own tissues rather than foreign invaders like bacteria or viruses. In the case of wAIHA, these autoantibodies specifically attack red blood cells at warm temperatures, meaning at normal body temperature of around 37 degrees Celsius or higher.[1][2]
Red blood cells carry oxygen throughout the body to every organ and tissue. When these cells are destroyed faster than the body can replace them, anaemia develops, which is a condition characterised by having too few red blood cells in the bloodstream. The process of red blood cell destruction is called hemolysis. While healthy red blood cells normally survive for about 115 to 120 days, in wAIHA they may be destroyed within days or even hours.[3][5]
The condition is classified as “warm” because the autoantibodies involved are most active at body temperature, distinguishing it from cold autoimmune haemolytic anaemia where the destructive antibodies are active at cooler temperatures. The most common type of antibody involved in warm autoimmune haemolytic anaemia is immunoglobulin G (IgG), the most prevalent antibody type in the human body.[2][4]
How Common Is This Condition
Warm autoimmune haemolytic anaemia is considered a rare disorder. Overall, autoimmune haemolytic anaemia affects approximately 1 to 3 out of every 100,000 people each year. Warm autoimmune haemolytic anaemia represents the most common subtype, comprising roughly 70 to 80 percent of all adult cases of autoimmune haemolytic anaemia, and about 50 percent of cases in children.[1][3]
The condition can affect anyone, but certain demographic patterns have been observed. It occurs most frequently in females over the age of 40 years. However, cases have been documented across all age groups, including infants and children, though it is very rare in younger populations. In children, the condition occurs at an even lower rate of approximately 0.2 per 100,000 people each year.[1][6]
The mortality rate associated with autoimmune haemolytic anaemia has been reported at around 11 percent in adults. In children, the mortality rate is lower at approximately 4 percent, but this can increase to 10 percent when the condition occurs alongside other immune disorders, such as when it appears together with immune thrombocytopenia in what is known as Evans syndrome.[6]
What Causes Warm Autoimmune Haemolytic Anaemia
The fundamental cause of warm autoimmune haemolytic anaemia lies in a malfunction of the immune system. The body begins producing autoantibodies that target proteins on the surface of its own red blood cells. These antibodies mark the red blood cells as foreign substances, triggering their destruction by immune cells, particularly macrophages located in the spleen and liver.[2][5]
In approximately half of all cases, the exact reason why the immune system begins producing these harmful autoantibodies remains unknown. When no underlying cause can be identified, the condition is referred to as primary or idiopathic warm autoimmune haemolytic anaemia. Some people may spontaneously start producing excessive amounts of these autoantibodies without any obvious trigger, though in some individuals this has been associated with prior infections, transplants, or blood transfusions.[1][5]
In the other half of cases, warm autoimmune haemolytic anaemia develops secondary to other medical conditions or external factors. Secondary wAIHA can be linked to other autoimmune diseases, where the immune system is already attacking various body tissues. These associated conditions include systemic lupus erythematosus, rheumatoid arthritis, Sjogren’s syndrome, thyroid disease, ulcerative colitis, and Hashimoto’s disease.[1][4]
Blood cancers, particularly lymphoproliferative disorders such as chronic lymphocytic leukaemia and lymphoma, are associated with approximately 20 percent of autoimmune haemolytic anaemia cases. Viral infections can also trigger the development of wAIHA, though in these cases the anaemia typically resolves once the infection is successfully treated. Viruses that may be linked to the condition include Epstein-Barr virus, measles, mumps, rubella, atypical pneumonia, and varicella, the virus that causes chickenpox.[1][6]
Certain medications have also been associated with the development of warm autoimmune haemolytic anaemia. Several classes of drugs can trigger this condition, including the antibiotic penicillin and related antibiotics such as cephalosporins, including ceftriaxone and cefotetan, as well as ciprofloxacin. Other medications linked to wAIHA include quinidine, nonsteroidal anti-inflammatory drugs, and alpha methyldopa.[4]
Risk Factors for Developing the Condition
Several factors can increase an individual’s risk of developing warm autoimmune haemolytic anaemia. Being female represents one demographic risk factor, as the condition occurs more commonly in women than in men. Age is another consideration, with the highest incidence observed in individuals over 40 years of age.[1]
Having an existing autoimmune disease significantly elevates the risk of developing wAIHA. People with conditions such as lupus, rheumatoid arthritis, or other disorders where the immune system attacks the body’s own tissues are at increased risk. Similarly, individuals diagnosed with certain blood cancers, particularly chronic lymphocytic leukaemia or lymphoma, face an elevated risk of developing secondary warm autoimmune haemolytic anaemia.[1][4]
Recent viral infections may increase susceptibility to developing wAIHA, particularly infections with viruses such as Epstein-Barr virus or other common viral illnesses. Additionally, individuals who have recently undergone organ transplantation or received blood transfusions may have an increased risk. Taking certain medications, especially those known to be associated with drug-induced wAIHA, also represents a risk factor.[1][5]
People with genetically defined immune dysregulation disorders or primary immunodeficiency syndromes also have a heightened risk. These conditions affect the normal functioning of the immune system and can predispose individuals to developing autoimmune complications, including warm autoimmune haemolytic anaemia.[3]
Signs and Symptoms
The symptoms of warm autoimmune haemolytic anaemia can range from mild to severe, and they reflect both the reduction in red blood cells and the body’s response to the destruction of these cells. Generally, symptoms develop gradually over the course of several weeks, although in some cases they can appear within just a few days.[1][5]
Profound fatigue is one of the most common and debilitating symptoms of wAIHA. This exhaustion occurs because the reduced number of red blood cells means less oxygen is being delivered to the body’s organs and tissues. The fatigue can be so severe that it significantly limits daily activities and quality of life. Alongside tiredness, people often experience weakness and dizziness, particularly when standing up or exerting themselves physically.[1][2]
Cardiovascular symptoms frequently occur as the heart attempts to compensate for the reduced oxygen-carrying capacity of the blood. These can include a rapid heartbeat or tachycardia, heart palpitations where the person becomes aware of their heartbeat, and shortness of breath or dyspnoea, especially during physical activity. Some individuals may experience chest pain or difficulty breathing even at rest.[1][5]
Jaundice, which is a yellowing of the skin and the whites of the eyes, commonly develops in people with wAIHA. This occurs because the breakdown of red blood cells releases a substance called bilirubin, which accumulates in the body faster than the liver can process it. The jaundice is often exacerbated in individuals who also have Gilbert’s syndrome, a common benign condition that affects bilirubin processing.[5][14]
Additional symptoms can include pale skin or pallor, which reflects the reduced number of red blood cells. Many people notice that their urine becomes darker in colour, sometimes described as tea-coloured or brown, due to the breakdown products of destroyed red blood cells being excreted through the kidneys. Headaches, muscle pain, and backache are also frequently reported.[1][5]
Some individuals experience gastrointestinal symptoms such as nausea, vomiting, or diarrhoea. A sore tongue may develop, and fever can occur. In more severe cases, confusion may be present, and the spleen may become enlarged, a condition called splenomegaly. People with wAIHA may also have an increased risk of developing blood clots, strokes, and other cardiovascular complications, as well as signs of heart failure in severe cases.[1][5]
Prevention Strategies
Preventing warm autoimmune haemolytic anaemia can be challenging, particularly for primary wAIHA where the cause is unknown. However, certain measures may help reduce the risk of developing secondary wAIHA or experiencing disease flares in those already diagnosed with the condition.
For individuals with existing autoimmune diseases, maintaining good control of the underlying condition through appropriate medical treatment may help reduce the risk of developing secondary wAIHA. Regular monitoring and compliance with prescribed treatments for conditions such as lupus or rheumatoid arthritis are important preventive measures.[1]
When medications are known to potentially trigger warm autoimmune haemolytic anaemia, healthcare providers can consider alternative treatments when possible. If someone has previously experienced drug-induced wAIHA, avoiding the causative medication and related drugs becomes essential. Always inform healthcare providers about any history of autoimmune haemolytic anaemia before starting new medications.[4]
Prompt treatment of infections may help prevent virus-triggered wAIHA in susceptible individuals. Maintaining overall immune system health through adequate nutrition, including supplementation with folic acid as recommended by healthcare providers, can support red blood cell production. Prophylactic folic acid is particularly important for those already diagnosed with wAIHA, as active hemolysis can consume folate and potentially worsen the condition.[8]
For people with known wAIHA, avoiding exposure to extreme temperatures and managing stress levels may help prevent flares. Regular medical follow-up allows for early detection of disease recurrence or worsening, enabling timely intervention. Individuals who have undergone splenectomy as treatment for wAIHA should take extra precautions against infections, as the spleen plays an important role in the immune system.[6]
How the Disease Affects the Body
The pathophysiology of warm autoimmune haemolytic anaemia involves a complex series of immune system malfunctions and physical changes to red blood cells that ultimately lead to their premature destruction. Understanding these mechanisms helps explain both the symptoms experienced and the rationale behind various treatments.[3]
The process begins when the immune system produces IgG autoantibodies that attach to proteins on the surface of red blood cells. These antibodies bind most effectively at body temperature of 37 degrees Celsius, which is why the condition is classified as “warm.” Once the antibodies attach to the red blood cells, they leave a portion called the FC region exposed on the cell surface.[2][4]
Macrophages, which are large immune cells found primarily in the spleen and liver, have receptors that recognize and bind to these FC regions. These macrophages essentially grab onto the antibody-coated red blood cells and remove portions of the cell membrane, similar to taking small bites out of the cells. This process occurs mainly in the reticuloendothelial system, particularly in the spleen.[4]
As red blood cells lose portions of their membrane, they become smaller and more spherical, transforming into cells called spherocytes. Unlike normal flexible red blood cells that can easily squeeze through small blood vessels, spherocytes are rigid and less deformable. This lack of flexibility causes them to become trapped in the narrow passages of the spleen, where they are singled out for complete destruction.[4]
The accumulation of trapped and destroyed red blood cells in the spleen causes the organ to enlarge, resulting in splenomegaly. This enlargement can be felt during physical examination and may cause discomfort in the left upper abdomen. The spleen becomes a major site of red blood cell destruction in this condition.[4]
When red blood cells are destroyed, they release their contents into the bloodstream. This includes haemoglobin, the oxygen-carrying protein inside red blood cells, which breaks down into several components. One breakdown product is bilirubin, which gives bile its yellow colour. When bilirubin accumulates faster than the liver can process it, it causes jaundice. Another protein called haptoglobin normally binds free haemoglobin in the blood, but it becomes depleted in wAIHA, and low haptoglobin levels become a useful diagnostic marker.[14]
The destruction of red blood cells also releases an enzyme called lactate dehydrogenase (LDH) from inside the cells, and levels of this enzyme become elevated in the blood. These biochemical changes, along with elevated unconjugated bilirubin and decreased haptoglobin levels, provide laboratory evidence of active hemolysis.[3][14]
The reduced oxygen delivery to tissues and organs caused by anaemia triggers multiple physiological responses. The heart increases its rate and force of contraction to circulate the oxygen-poor blood more rapidly, which explains the rapid heartbeat and palpitations. Breathing rate increases in an attempt to bring more oxygen into the lungs. Despite these compensations, tissues remain oxygen-deprived, leading to fatigue, weakness, and potential organ dysfunction if the anaemia becomes severe.[2]
In some cases, particularly when the antibody levels are very high or the antibodies have certain characteristics, red blood cell destruction can occur directly in the bloodstream rather than only in the spleen and liver. This intravascular hemolysis can be more dangerous and may lead to kidney damage if the breakdown products accumulate in the kidneys.[3]
The ongoing immune system activation in wAIHA can also increase the risk of blood clot formation, even though the condition primarily involves red blood cell destruction. The mechanisms behind this increased thrombotic risk are complex and involve inflammation, changes in blood vessel lining cells, and alterations in blood flow patterns caused by anaemia and splenomegaly.[5]
