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PubMed This is a summary of 18 peer-reviewed journal articles Updated
Hematology

The Types of AIHA: Warm, Cold, Mixed, and PCH

At a Glance

Autoimmune Hemolytic Anemia (AIHA) is divided into four main subtypes based on the temperature at which antibodies attack red blood cells: warm, cold, mixed, and PCH. Identifying your exact subtype is critical because each type uses different biological mechanisms and requires a different treatment approach.

Identifying the exact subtype of Autoimmune Hemolytic Anemia (AIHA) is perhaps the most critical step in your care. While all forms of AIHA involve the immune system attacking red blood cells, the “how,” “when,” and “where” of that attack change depending on the subtype. Because the biological mechanisms are different, a treatment that works for one type may be completely ineffective for another [1][2].

The Role of Antibodies and Temperature

The immune system uses different types of proteins called antibodies to mark cells. In AIHA, these antibodies are classified by the temperature at which they are most active—their “thermal reactivity.”

  • Warm Antibodies (IgG): These are most active at normal body temperature (37°C or 98.6°F) [3].
  • Cold Antibodies (IgM): These are most active at temperatures below normal body temperature [4][5].

The Four Main Subtypes

The following table breaks down the key differences between the four primary types of AIHA.

Subtype Primary Antibody Optimal Temperature Key Feature
Warm AIHA (wAIHA) IgG Body Temp (37°C) Most common type; cells are usually destroyed in the spleen [3][6].
Cold Agglutinin Disease (CAD) IgM Cold (<30°C) Causes cells to agglutinate (clump together) in cold extremities (fingers, toes) [4][7].
Mixed AIHA IgG & IgM Both Combines features of both warm and cold types; often more severe [8][9].
Paroxysmal Cold Hemoglobinuria (PCH) IgG (Donath-Landsteiner) Cold then Warm A rare “biphasic” antibody binds in the cold and destroys cells when they rewarm [10][11].

1. Warm AIHA (wAIHA)

This is the most frequent form of the disease. The IgG antibodies coat the red blood cells, which are then recognized as “foreign” by the spleen and removed from circulation [6]. Because it reacts at body temperature, the destruction happens continuously [3].

2. Cold Agglutinin Disease (CAD)

In CAD, IgM antibodies attach to red blood cells when you are exposed to cold. This triggers the complement system—a group of proteins in the blood that help the immune system destroy targets [7][5]. Patients may notice symptoms like pain or a bluish tint in their fingers or toes when it is cold.

3. Mixed-Type AIHA

Mixed AIHA is rare and involves both warm (IgG) and cold (IgM or C3d) reactivity [8]. Because two different mechanisms are attacking the red blood cells at once, this type can sometimes be harder to treat and may require more intensive management [9].

4. Paroxysmal Cold Hemoglobinuria (PCH)

PCH is caused by the unique Donath-Landsteiner antibody. This antibody is “biphasic,” meaning it requires two steps to work: it first attaches to cells in the cold, and then causes them to burst (hemolysis) once the body warms back up [10][12]. While PCH is more common in children following a virus, it can occur in adults [13][11].

Evans Syndrome: A Double Challenge

Sometimes, the immune system doesn’t stop at red blood cells. Evans Syndrome occurs when a patient has AIHA plus Immune Thrombocytopenia (ITP), a condition where the body also destroys platelets (the cells that help your blood clot) [14][15]. Managing Evans Syndrome is often more complex because the doctor must protect two different types of blood cells simultaneously [16].

Why Subtyping Is Mandatory

Your subtype dictates your treatment “roadmap.” For example, corticosteroids (like prednisone) are the standard first-line treatment for warm AIHA, but they are generally ineffective for Cold Agglutinin Disease [1][2]. Conversely, new complement inhibitors specifically target the mechanisms found in cold types but may not help with warm types [17][18]. Knowing your subtype ensures you are receiving the right medicine for your specific biological “lock and key.”

Return to Overview | Next: Diagnosis & Lab Reports

Common questions in this guide

What is the difference between warm and cold AIHA?
Warm AIHA involves antibodies that are most active at normal body temperature, often destroying red blood cells in the spleen. Cold AIHA, or Cold Agglutinin Disease, involves antibodies that attack red blood cells when the body is exposed to cold temperatures.
Why does my AIHA subtype matter for treatment?
Different subtypes use different biological mechanisms to attack red blood cells. For example, corticosteroids are the standard treatment for warm AIHA but are generally ineffective for cold types, which may require specific complement inhibitors instead.
What is Evans Syndrome?
Evans Syndrome is a condition where a person has AIHA combined with Immune Thrombocytopenia (ITP). This means the immune system is destroying both red blood cells and platelets, making it more complex for doctors to manage.
How does a doctor determine my AIHA subtype?
Doctors use a blood test called a Direct Antiglobulin Test (DAT) to see which specific antibodies or proteins are coating your red blood cells. The results show whether your immune system is using warm, cold, or mixed antibodies.
What is Paroxysmal Cold Hemoglobinuria (PCH)?
PCH is a rare type of AIHA caused by a unique antibody that attaches to red blood cells in the cold and destroys them when the body warms back up. It is most commonly seen in children following a viral infection but can also occur in adults.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Based on my test results, do I have the 'warm' or 'cold' subtype of AIHA, or a mixture of both?
  2. 2.Was my Direct Antiglobulin Test (DAT) positive for IgG, C3d, or both? How does this confirm my subtype?
  3. 3.If I have cold agglutinin disease, is my treatment plan different than if I had the warm type?
  4. 4.Is my platelet count normal, or is there any sign of Evans Syndrome?
  5. 5.Was a Donath-Landsteiner test performed to rule out PCH, especially if my symptoms started after a virus?

Questions For You

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References

References (18)
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This page explains the different subtypes of AIHA for educational purposes only. Always consult your hematologist to understand your specific diagnosis and treatment plan.

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