From the Guidelines
The diagnosis of autoimmune hemolytic anemia (AIHA) should be approached with a comprehensive laboratory work-up, including a complete blood count (CBC), reticulocyte count, peripheral blood smear, lactate dehydrogenase (LDH), haptoglobin, bilirubin, and the direct antiglobulin test (DAT or Coombs test) as the cornerstone of diagnosis, as recommended by the most recent guidelines 1. The initial evaluation should include a thorough history and physical examination, with consideration of new drugs, insect, spider, or snake bites, and a CBC with evidence of anemia, macrocytosis, and evidence of hemolysis on peripheral smear. Key laboratory tests to confirm hemolysis and identify its autoimmune nature include:
- Blood chemistry
- CBC with evidence of anemia and macrocytosis
- LDH
- Haptoglobin
- Bilirubin
- Reticulocyte count
- Free hemoglobin
- Disseminated intravascular coagulation panel
- Autoimmune serology
- Paroxysmal nocturnal hemoglobinuria screening
- Direct and indirect bilirubin
- Direct agglutinin test
- Bone marrow analysis and cytogenetic analysis if no obvious cause is found
- Evaluation for viral/bacterial causes of hemolysis
- Protein electrophoresis and cryoglobulin analysis
- Work-up for bone marrow failure syndrome if refractory
- Glucose-6-phosphate dehydrogenase evaluation
- Assessment of common drug causes and methemoglobinemia, as outlined in the American Society of Clinical Oncology clinical practice guideline 1. The direct antiglobulin test (DAT or Coombs test) is crucial in diagnosing AIHA, as it detects antibodies or complement bound to red blood cells, and additional testing such as indirect antiglobulin test, cold agglutinin titers, and testing for underlying conditions like complete metabolic panel, ANA, and viral serologies may be necessary to guide appropriate treatment 1.
From the Research
Diagnosis of Autoimmune Hemolytic Anemia
To diagnose autoimmune hemolytic anemia (AIHA), several laboratory tests can be employed. The key tests include:
- Direct antiglobulin test (DAT) to detect antibodies or complement attached to red blood cells
- Indirect antiglobulin test to detect free antibodies in the serum
- Reticulocyte count to assess bone marrow activity
- Complete blood count (CBC) to evaluate anemia and other blood cell abnormalities
Laboratory Tests for AIHA
The following laboratory tests are useful in the diagnosis of AIHA:
- Direct antiglobulin test (DAT) to confirm the presence of autoantibodies or complement on the red blood cells 2, 3
- Tests to detect low-affinity IgG and IgA/IgM autoantibodies in cases with negative DAT results 4, 5
- Column method-DAT before and after washing red blood cells to classify DAT-negative AIHA into different subgroups 6
Classification of DAT-Negative AIHA
DAT-negative AIHA can be classified into several subgroups, including:
- Tube DAT-negative
- Low-affinity IgG
- Double DAT-negative
- IgA- or IgM-positive
- Low-affinity IgM
- Suspected non-AIHA 6 These subgroups have different clinical characteristics and responses to treatment, highlighting the importance of accurate diagnosis and classification 6
Diagnostic Approach
A systematic approach to diagnosis is critical, and the following steps can be taken:
- Perform DAT and other initial tests to establish the diagnosis of AIHA 2, 3
- Conduct additional tests, such as those for low-affinity IgG and IgA/IgM autoantibodies, if DAT is negative 4, 5
- Use a comprehensive classification system, such as the one based on RBC-bound IgG levels and column method-DAT results, to categorize DAT-negative AIHA 6