Autoimmune hemolytic anemia (AIHA) is a blood disorder in which your immune system mistakenly produces antibodies that attack and destroy your own red blood cells. This destruction happens faster than your body can replace them, leading to anemia. It affects roughly 1.4 to 6.6 people per 100,000 each year in the United States, occurs more often in women than men, and becomes more common with age.
How AIHA Destroys Red Blood Cells
Normally, antibodies target bacteria, viruses, and other foreign invaders. In AIHA, they latch onto the surface of your own red blood cells and mark them for destruction. Your spleen, which filters blood and removes damaged cells, is the primary site where this destruction takes place. The spleen’s immune cells recognize the antibody-tagged red blood cells and break them down far earlier than their normal 120-day lifespan.
When red blood cells are destroyed in large numbers, the breakdown products spill into your bloodstream. Bilirubin, a yellow pigment released from dying red cells, builds up and causes jaundice. Your bone marrow tries to compensate by producing new red blood cells at an accelerated rate, but in moderate to severe cases it simply can’t keep up.
Warm AIHA vs. Cold Agglutinin Disease
AIHA comes in two main forms, defined by the type of antibody involved and the temperature at which it becomes active.
Warm AIHA is the more common type. It involves IgG antibodies that attack red blood cells at normal body temperature (98.6°F or higher). Because your body is always at this temperature, the destruction is constant and tends to cause steady, progressive anemia. Most cases of warm AIHA are either idiopathic (no identifiable cause) or linked to another underlying condition.
Cold agglutinin disease involves IgM antibodies that activate when red blood cells cool below core body temperature. This happens in your extremities: fingertips, toes, ears, and nose. In cold environments, these antibodies clump red blood cells together and trigger their destruction. People with cold agglutinin disease often experience bluish discoloration (cyanosis) in their fingers and ears during cold exposure, on top of the anemia symptoms. The closer these cold-reactive antibodies can function to normal body temperature, the more severe the disease tends to be.
Common Symptoms
The symptoms of AIHA reflect two things happening at once: the anemia itself and the byproducts of red blood cell destruction. You may notice unusual weakness and fatigue that feels out of proportion to your activity level. A rapid heartbeat and shortness of breath, especially during exertion, are common because your blood carries less oxygen than it should.
Jaundice, a yellowing of the skin and whites of the eyes, develops as bilirubin accumulates. Your urine may turn dark brown or tea-colored from the breakdown products filtered through your kidneys. Some people develop an enlarged spleen, which a doctor can sometimes feel during a physical exam. In cold agglutinin disease, cold-induced color changes in the fingers and ears are an additional hallmark.
Symptoms can appear gradually over weeks or erupt suddenly in a hemolytic crisis, where red blood cell destruction accelerates rapidly. The severity varies widely. Some people have mild anemia they barely notice, while others become dangerously anemic and need urgent treatment.
What Causes It
In many cases, warm AIHA arises on its own with no identifiable trigger. This is called primary or idiopathic AIHA. But roughly half the time, AIHA develops alongside another medical condition or in response to a medication.
Autoimmune diseases like lupus are well-known triggers. Blood cancers, particularly lymphomas and chronic lymphocytic leukemia, can also provoke AIHA because they disrupt normal immune function. Certain medications are capable of triggering an immune response against red blood cells. The most commonly implicated drug classes include cephalosporin antibiotics, penicillin and its derivatives, some NSAIDs, and a handful of other medications including levodopa, nitrofurantoin, and methyldopa. When a drug is the cause, stopping the medication usually resolves the anemia.
How AIHA Is Diagnosed
The key diagnostic test is the direct antiglobulin test, often called the direct Coombs test. It detects antibodies or proteins stuck to the surface of your red blood cells. This single test establishes the diagnosis and helps determine whether you have warm or cold AIHA based on the pattern of antibodies found.
In warm AIHA, the test typically shows IgG antibodies on the red blood cell surface. In cold agglutinin disease, a complement protein called C3 is found instead, and doctors measure the cold agglutinin titer, which gauges how concentrated the cold-reactive antibodies are in your blood. A titer of 1:64 or higher supports the diagnosis, though most patients have much higher levels.
Other blood tests fill in the picture. Lactate dehydrogenase (an enzyme released from damaged cells) and indirect bilirubin are typically elevated. Haptoglobin, a protein that normally mops up free hemoglobin in your blood, drops to very low levels because it gets used up during red blood cell destruction. A blood smear under the microscope often reveals microspherocytes, small round red blood cells that form when the spleen partially chews away at antibody-coated cells without fully destroying them. The reticulocyte count, which measures immature red blood cells, is usually high, reflecting the bone marrow’s effort to replace what’s being lost.
Treatment for Warm AIHA
Corticosteroids are the standard first treatment for warm AIHA. They work by suppressing the immune response that’s driving the red blood cell destruction. Most people start on a dose calibrated to their body weight, which is maintained for one to three weeks until hemoglobin levels stabilize above 10 g/dL (a threshold where most people feel significantly better). The dose is then gradually tapered over weeks to months.
Many people respond well to steroids initially, but the challenge is staying in remission once the dose comes down. If the anemia returns during tapering, if you need more than a low maintenance dose to keep it controlled, or if steroids don’t work at all, second-line options come into play.
Spleen removal (splenectomy) has long been considered the most effective second-line treatment, since the spleen is the main site where tagged red blood cells are destroyed. Removing it can produce lasting remission in many patients. However, a targeted therapy called rituximab, which depletes the specific immune cells that produce the harmful antibodies, is increasingly used before splenectomy. It offers a way to avoid surgery entirely in some cases and is moving earlier in treatment algorithms as doctors gain more experience with it.
Managing Cold Agglutinin Disease
Cold agglutinin disease requires a different approach because corticosteroids and splenectomy are generally less effective for this subtype. The cornerstone of management is avoiding cold exposure. That means keeping your extremities warm, avoiding cold showers and cold beverages during flares, and being cautious in cold climates.
In hospital settings, rooms are kept warm and any blood transfusions are delivered through an in-line blood warmer. Without warming, transfused blood can trigger further hemolysis and even cause the transfusion line to clot. For people living in colder climates, symptoms tend to be seasonal and can range from mild discomfort to disabling anemia. When cold avoidance alone isn’t enough, targeted therapies that address the underlying immune dysfunction are used.
Blood Clot Risk
One underappreciated complication of AIHA is a significantly elevated risk of blood clots. In one retrospective study, 29% of AIHA patients developed a blood clot compared to 19% of matched patients without AIHA. The odds of clotting were roughly 2.4 times higher with AIHA. Deep vein thrombosis in the arms or legs was the most common type, followed by pulmonary embolism (a clot that travels to the lungs). The exact mechanism isn’t fully understood, but the process of red blood cell destruction releases substances that activate clotting pathways. This risk is something both patients and their doctors need to be aware of, particularly during active hemolysis.
Long-Term Outlook
The course of AIHA is unpredictable. Some people have a single episode that resolves with treatment and never returns. Others experience a relapsing pattern where the anemia comes back months or years later, sometimes requiring multiple rounds of therapy. When AIHA is secondary to another condition like lupus or lymphoma, treating the underlying disease often improves the anemia as well.
Drug-induced AIHA generally has the best prognosis. Once the offending medication is stopped, the immune attack on red blood cells typically winds down over days to weeks, and most people recover completely without lasting effects. For idiopathic warm AIHA, the majority of patients respond to first-line therapy, but a meaningful percentage will need second-line treatment at some point. Cold agglutinin disease tends to be chronic but manageable, especially when patients can minimize cold exposure and access targeted treatment when needed.