Autoimmune hemolytic anemia (AIHA) is a condition in which the immune system makes antibodies against the body’s own red blood cells, so they are destroyed faster than the bone marrow can replace them. It is diagnosed by finding anemia, laboratory signs of red cell breakdown, and a positive direct antiglobulin test (the Coombs test). Treatment depends mainly on whether the antibodies are “warm” or “cold”, and on whether another disease is driving them.
As a clinical pathologist with a focus on hematology, I see AIHA as a disorder with complex dynamics: the pace of destruction, the marrow’s ability to compensate, and the antibody type all shape how a patient looks and how they are treated. This guide untangles those moving parts.
What Happens in AIHA?
A healthy red blood cell survives about 120 days before it is recycled. In AIHA, autoantibodies coat the red cell surface. Coated cells are either removed by macrophages in the spleen and liver (extravascular hemolysis) or, when complement is strongly activated, burst inside the blood vessels (intravascular hemolysis).
The marrow responds by increasing production, releasing young red cells called reticulocytes. If production keeps pace, the anemia may be mild. If destruction outruns production, hemoglobin falls, sometimes quickly. This balance between destruction and compensation is why two patients with the same diagnosis can feel very different. For a broader view of red cell loss, see our anemia guide.
Types of AIHA
AIHA is classified by the temperature at which the antibody binds best, which also reflects the antibody class and the main site of destruction.
| Type | Usual antibody | Typical DAT result | Main features |
|---|---|---|---|
| Warm AIHA | IgG, binds at body temperature | IgG positive, with or without C3 | Most common form; spherocytes on smear; destruction mainly in the spleen |
| Cold agglutinin disease | IgM, binds in cooler parts of the body | C3 positive, IgG negative | Red cell clumping; symptoms worse in cold, such as blue or numb fingers |
| Mixed AIHA | Both warm and cold antibodies | IgG and C3 positive | Uncommon; often more severe |
| Paroxysmal cold hemoglobinuria | IgG Donath-Landsteiner antibody | C3 positive | Rare; classically follows viral infection in children |
Causes and Risk Factors
AIHA is called primary (idiopathic) when no underlying cause is found, and secondary when it is linked to another condition. Common secondary causes include:
- Lymphoproliferative disorders, especially chronic lymphocytic leukemia and some lymphomas
- Autoimmune diseases such as systemic lupus erythematosus
- Infections, including Mycoplasma pneumoniae and Epstein-Barr virus (often causing transient cold antibodies)
- Immune deficiency states
- Certain medications, and some cancer immunotherapies
- Previous stem cell or organ transplantation
Drug-induced immune hemolysis is usually treated simply by stopping the drug, which is why a careful medication history is part of every workup.
Symptoms and Clinical Presentation
Symptoms come from two sources: the anemia itself and the breakdown products of red cells.
- From anemia: fatigue, weakness, pallor, breathlessness on exertion, and a racing heart
- From hemolysis: jaundice (yellow eyes or skin), dark urine, and sometimes an enlarged spleen
- In cold disease: color changes and numbness in the fingers, toes, ears, or nose in cold weather
Onset can be gradual over weeks or sudden over days. A rapid fall in hemoglobin, with chest pain or confusion, is a medical emergency.
Diagnosis and Testing
The workup confirms that red cells are being destroyed, shows that the destruction is immune-mediated, and then looks for a cause.
| Test | Typical finding in AIHA | What it shows |
|---|---|---|
| Hemoglobin | Low | Degree of anemia |
| Reticulocyte count | Usually raised | Marrow is trying to compensate |
| Lactate dehydrogenase (LDH) | Raised | Released from broken red cells |
| Indirect (unconjugated) bilirubin | Raised | Breakdown of hemoglobin |
| Haptoglobin | Low | Consumed by binding free hemoglobin |
| Direct antiglobulin test (Coombs) | Positive | Antibody or complement on red cells |
| Blood smear | Spherocytes (warm) or agglutination (cold) | Pattern of damage |
A normal or low reticulocyte count despite hemolysis is a warning sign. It can mean the antibodies are also targeting young cells or that the marrow is affected, and it often prompts a closer look. Further tests may include a cold agglutinin titer, immunoglobulin studies, and imaging or marrow examination to exclude an underlying lymphoma.
Treatment Options
Warm AIHA
- Corticosteroids such as prednisone are first-line and control hemolysis in most patients, followed by a slow taper.
- Rituximab, an antibody that depletes B-cells, is used for disease that relapses or does not respond, and increasingly earlier.
- Other immunosuppressants, such as azathioprine or mycophenolate, may be used as steroid-sparing agents.
- Splenectomy is considered when drug treatment fails, since the spleen is the main site of destruction.
Cold Agglutinin Disease
- Keeping warm is the foundation: warm clothing, gloves, and avoiding cold drinks and exposure.
- Steroids work poorly in cold disease and are generally not used as main therapy.
- Rituximab-based treatment and complement inhibitors are options for symptomatic disease.
Supportive Care
Folic acid supports the increased red cell production. Blood transfusion is given for severe or symptomatic anemia; matching is harder because the antibodies react with most donor cells, but transfusion should not be withheld when it is needed. In cold disease, blood is given through a warmer. Patients on long-term steroids also need attention to bone health, blood sugar, and infection risk.
When to See a Doctor
Seek urgent care if you develop yellow eyes, dark or cola-colored urine, marked breathlessness, chest pain, or dizziness, especially with a known diagnosis of AIHA. People already on treatment should report fever and new fatigue promptly, as relapse can occur when steroids are reduced.
Frequently Asked Questions
Is AIHA curable?
Many patients reach long remissions with treatment, and secondary AIHA often improves when the underlying cause is treated. Relapses are common, however, so ongoing follow-up with blood counts is part of care.
Can a positive Coombs test occur without AIHA?
Yes. A positive direct antiglobulin test can be seen in some healthy people and in some hospitalized patients without hemolysis. AIHA is diagnosed only when a positive test is combined with anemia and laboratory evidence of red cell destruction.
Why does cold weather make some people’s AIHA worse?
In cold agglutinin disease, the IgM antibodies bind red cells in cooler parts of the body such as fingers and ears. Cold exposure increases binding, clumping, and complement activation, which worsens both circulation symptoms and hemolysis.
Is AIHA hereditary?
AIHA is an acquired immune disorder rather than an inherited one. A family history of autoimmune disease may add some susceptibility, but it is not passed on in a predictable way.
Key Takeaways
- AIHA is immune destruction of red cells, confirmed by hemolysis labs and a positive Coombs test.
- Warm and cold types differ in antibody, symptoms, and treatment.
- Secondary causes such as lymphoma, lupus, and drugs must always be looked for.
- Steroids are first-line for warm AIHA; warmth and targeted therapy are central in cold disease.
