How Common Is Autoimmune Haemolytic Anaemia?

Autoimmune haemolytic anaemia is a rare condition that affects only a small number of people each year. Studies show that approximately 1 to 3 people out of every 100,000 develop this disorder annually^[1][6]. While the condition can occur at any age, it most commonly affects women over the age of 40^[1]. The disorder appears to have a higher prevalence rate of about 17 cases per 100,000 people in the general population^[10].

AIHA is classified into different types based on when and how the immune system attacks red blood cells. The most common form is warm autoimmune haemolytic anaemia, which accounts for the majority of cases. Cold autoimmune haemolytic anaemia, also known as cold agglutinin disease (a condition where antibodies attack red blood cells at cooler temperatures), is much rarer, affecting only about 1 person per million each year^[2][6]. This cold antibody type typically develops in people between 40 and 80 years of age.

In children, AIHA is extremely uncommon, with an estimated incidence of only 0.2 cases per 100,000 children per year^[10]. When the condition does occur in young people, it is often associated with immune system disorders. Children diagnosed with AIHA generally have a better outlook than adults, with a mortality rate of about 4%, although this increases to 10% when the anaemia occurs alongside a reduction in blood platelets, a combination known as Evans syndrome^[10].

What Causes This Condition?

The exact reasons why the immune system begins attacking its own red blood cells remain poorly understood. In about half of all cases, doctors cannot identify a clear cause, and the condition is described as idiopathic or primary AIHA^[1][2]. This means the disorder appears without any obvious underlying illness or trigger. These cases account for more than 60% of unselected patients with AIHA^[2].

In the remaining cases, AIHA develops as a secondary condition linked to another health problem. The most common underlying causes are blood-related cancers, particularly chronic lymphocytic leukaemia and lymphoma, which are responsible for about 20% of secondary cases^[10]. Autoimmune diseases such as systemic lupus erythematosus (a condition where the immune system attacks many parts of the body), rheumatoid arthritis, ulcerative colitis, and thyroid disorders are also frequently associated with AIHA^[1][2].

Infections can trigger the development of AIHA as well, although the anaemia often resolves once the infection is treated. Viral infections are particularly common culprits. Epstein-Barr virus, which causes infectious mononucleosis, cytomegalovirus, hepatitis viruses, HIV, and the varicella virus that causes chickenpox have all been linked to AIHA^[1][6]. Bacterial infections such as atypical pneumonia caused by Mycoplasma bacteria can also lead to this condition.

Certain medications are known to occasionally cause AIHA. Antibiotics such as penicillin, drugs used to treat high blood pressure like methyldopa, antimalarial medications including quinine, and sulfonamide antibiotics have been reported to trigger red blood cell destruction^[6]. Additionally, some anti-inflammatory drugs and anticancer medications may be associated with the development of AIHA. In very rare instances, the condition has been observed following blood and bone marrow stem cell transplants^[2][3].

Who Is Most at Risk?

While autoimmune haemolytic anaemia can develop in anyone, certain groups face higher risks. Women are more likely to develop AIHA than men, and the condition most frequently appears after the age of 40^[1]. However, no one is immune, as cases have been documented across all age groups, from infants to the elderly.

People with existing autoimmune conditions carry an elevated risk of developing AIHA. Those diagnosed with lupus, rheumatoid arthritis, Sjogren’s syndrome, Hashimoto’s disease, or inflammatory bowel diseases such as Crohn’s disease or ulcerative colitis should be aware of this potential complication^[1][2]. Similarly, individuals with immune system disorders such as common variable immunodeficiency or autoimmune lymphoproliferative syndrome are at increased risk.

Patients with blood cancers face a particularly high risk of developing secondary AIHA. Chronic lymphocytic leukaemia and both Hodgkin and non-Hodgkin lymphoma are strongly associated with the condition^[6]. Anyone undergoing treatment for these cancers should be monitored for signs of anaemia.

Infection with certain viruses temporarily increases the risk of AIHA. People who contract Epstein-Barr virus, measles, mumps, rubella, or viral pneumonia may develop haemolytic anaemia during the course of their illness^[1]. Those with chronic viral infections such as HIV or hepatitis also face ongoing risk.

Medication use represents another risk factor. Patients taking antibiotics, particularly penicillin, or those on long-term treatment with certain blood pressure medications, antimalarials, or anti-inflammatory drugs should be aware of the potential for drug-induced AIHA^[6]. While genetic factors may play a role in a very small number of families, AIHA is not generally considered a hereditary condition^[3].

Recognising the Symptoms

The symptoms of autoimmune haemolytic anaemia can vary widely depending on how quickly red blood cells are being destroyed and how severe the anaemia becomes. Some people experience no symptoms at all, especially when red blood cell destruction happens gradually and the body has time to adjust^[5]. Others develop symptoms suddenly and experience severe, life-threatening complications within days.

The most common symptoms relate directly to the lack of oxygen-carrying red blood cells in the bloodstream. Persistent tiredness and weakness are often the first signs people notice. Many patients report feeling exhausted even after adequate rest. Shortness of breath may develop, initially during physical activity but potentially progressing to occur even at rest^[1][2]. The heart may beat faster than normal or feel like it’s pounding, as it works harder to deliver oxygen to tissues with fewer red blood cells available.

Skin changes are another hallmark of AIHA. Paleness, particularly noticeable in the face, palms, and nail beds, results from reduced red blood cells in the skin’s tiny blood vessels. Jaundice, or yellowing of the skin and the whites of the eyes, occurs when broken-down red blood cells release a yellow pigment called bilirubin^[1][2]. This same bilirubin causes urine to appear dark brown or tea-coloured, which can be alarming to patients.

Additional symptoms may include fever, headaches, muscle pain, nausea, vomiting, and diarrhoea^[1]. Some patients notice that their tongue becomes sore. An enlarged spleen, located in the upper left part of the abdomen, can create a sensation of fullness or discomfort in the belly^[5]. This happens because the spleen works overtime to filter out damaged red blood cells.

People with the cold antibody type of AIHA experience unique symptoms related to cold exposure. Their hands and feet may feel cold and appear blue, grey, or reddish when exposed to cool temperatures^[1][6]. Some develop chest pain or pain in the backs of their legs. In severe cases, inadequate blood flow to the extremities can cause complications similar to Raynaud’s phenomenon. The symptoms may be triggered by drinking cold water or washing hands in cold water, as even limited cold exposure can activate antibodies that destroy red blood cells^[5].

Prevention Strategies

Because the exact causes of primary autoimmune haemolytic anaemia remain unknown, there are no guaranteed methods to prevent the condition from developing initially. However, certain strategies may help reduce risk or prevent disease flares, particularly in cases of secondary AIHA.

For individuals with underlying autoimmune diseases or blood cancers, careful management of these primary conditions represents the most important preventive measure. Keeping conditions like lupus, rheumatoid arthritis, or chronic lymphocytic leukaemia under good control with appropriate medical treatment may reduce the likelihood of developing AIHA as a complication^[1].

Medication awareness is crucial. Patients should inform all their healthcare providers about any personal or family history of blood disorders or autoimmune conditions. When starting new medications, especially antibiotics or anti-inflammatory drugs, it’s important to be alert for signs of anaemia and report them promptly^[6]. If drug-induced AIHA is caught early and the offending medication is stopped quickly, the condition often resolves.

For people with cold antibody haemolytic anaemia, avoiding cold exposure is an important preventive measure. Staying warm in cold weather, wearing gloves and warm socks, avoiding cold water, and even being cautious about consuming cold foods or drinks can help prevent symptom flares^[5]. Some patients find they need to relocate to warmer climates or make significant lifestyle adjustments to manage their condition.

Prompt treatment of infections, particularly viral illnesses known to trigger AIHA, may help prevent the development of secondary anaemia. Individuals at high risk should seek medical care early when they develop symptoms of infection, and those with chronic viral infections like HIV should maintain consistent antiviral treatment.

Regular medical monitoring is essential for people at increased risk. Those with autoimmune diseases, blood cancers, or immune deficiency disorders should undergo periodic blood tests to check for early signs of anaemia, allowing for intervention before severe symptoms develop^[3]. This proactive approach doesn’t prevent AIHA but enables early detection and treatment.

How the Body Is Affected

Understanding what happens inside the body during autoimmune haemolytic anaemia helps explain the symptoms patients experience. Normally, red blood cells circulate in the bloodstream for about 100 to 120 days, carrying oxygen from the lungs to every tissue and organ^[3][6]. In AIHA, this lifespan is drastically shortened, sometimes to just a few days or even hours in severe cases.

The destruction process begins when the immune system produces antibodies (specialised proteins designed to fight foreign invaders) that mistakenly recognise red blood cells as threats. These antibodies attach to the surface of red blood cells, marking them for destruction. The type of antibody involved determines the classification of AIHA^[1][2].

In warm autoimmune haemolytic anaemia, IgG antibodies bind to red blood cells at normal body temperature. Once marked, these cells are primarily destroyed in the spleen, liver, and other organs by specialised immune cells called macrophages. This process, known as extravascular haemolysis (destruction outside blood vessels), happens gradually, which is why symptoms often develop over several weeks^[1].

Cold autoimmune haemolytic anaemia involves IgM antibodies that become active at temperatures below normal body temperature. These antibodies trigger a different destruction mechanism involving complement proteins, which are part of the immune system’s attack machinery. When complement proteins are activated, they can destroy red blood cells directly in the bloodstream, a process called intravascular haemolysis^[1][2]. This more violent destruction releases haemoglobin directly into the blood and can cause more severe symptoms.

As red blood cells break down, their contents are released into the bloodstream. Haemoglobin, the oxygen-carrying protein inside red blood cells, is broken down into bilirubin, causing jaundice. When destruction occurs in the bloodstream, free haemoglobin passes through the kidneys and appears in the urine, turning it dark. A protein called haptoglobin, which normally binds and clears haemoglobin, becomes depleted, and another enzyme called lactate dehydrogenase rises to high levels^[4].

The bone marrow attempts to compensate for the rapid red blood cell loss by dramatically increasing production. Young, immature red blood cells called reticulocytes are released into the bloodstream in higher numbers than normal^[2][4]. However, in many cases, the bone marrow cannot keep pace with the destruction, and anaemia worsens. In some patients, the immune attack extends to immature red blood cells in the bone marrow itself, further impairing the body’s ability to respond.

The spleen often enlarges in AIHA because it works overtime to filter out antibody-coated red blood cells. This enlargement can cause abdominal discomfort and contributes to the ongoing destruction of red blood cells^[5]. The reduced oxygen-carrying capacity of the blood forces the heart to work harder, leading to rapid heart rate and potentially causing strain on the cardiovascular system, especially in people with pre-existing heart conditions.