From the Guidelines
The Direct Antiglobulin Test (DAT) is positive in Cold Agglutinin Disease (CAD).
Rationale
- The DAT, also known as the Coombs test, is used to detect antibodies or complement proteins that are bound to the surface of red blood cells 1.
- In CAD, cold agglutinins (autoantibodies) bind to red blood cells at cold temperatures, leading to their agglutination and hemolysis.
- The presence of these autoantibodies on the surface of red blood cells would result in a positive DAT.
Evidence Support
- The provided evidence 1 mentions the Coombs test as a recommended test for hemolysis in the context of Waldenström's macroglobulinemia, which can be associated with CAD.
- Although the evidence does not directly state the result of the DAT in CAD, the underlying principle of the test supports a positive result in the presence of cold agglutinins.
Clinical Implication
- A positive DAT in CAD indicates the presence of autoantibodies or complement proteins on the surface of red blood cells, which can aid in the diagnosis and management of the disease.
From the Research
Direct Antiglobulin Test (DAT) Results in Cold Agglutinin Disease (CAD)
- The DAT result in CAD can be positive, specifically with anti-C3d and/or IgM antisera, as seen in studies 2, 3, 4.
- A positive DAT with C3d is characteristic of CAD, as the disease is mediated by cold-reactive IgM antibodies that activate the complement system 2, 3.
- In some cases, the DAT may be positive for both IgG and C3d, indicating a mixed autoimmune hemolytic anemia (AIHA) with both warm and cold autoantibodies 2.
- However, it is also possible for the DAT to be negative in some cases of CAD, particularly if the cold agglutinin titer is low, as reported in a study 5.
Clinical Implications of DAT Results in CAD
- A positive DAT result can help confirm the diagnosis of CAD, especially when combined with other laboratory findings such as elevated cold agglutinin titers and evidence of hemolysis 6, 4.
- The DAT result can also guide treatment decisions, as patients with CAD may require different therapies than those with warm AIHA, such as avoiding cold exposure and using complement inhibitors 2, 3.
- In some cases, a negative DAT result may not rule out CAD, and further testing may be necessary to confirm the diagnosis, as seen in a study 5.