The direct antiglobulin test will be positive in which of these conditions?

The direct antiglobulin test (DAT), also known as the Coombs test, is used to detect antibodies that are bound to the surface of red blood cells. When a condition causes the immune system to bind antibodies to these cells, the test will yield a positive result.

Hemolytic disease of the fetus and newborn (HDFN) occurs when the mother's immune system produces antibodies against fetal red blood cells, typically due to Rh incompatibility. These maternal antibodies can cross the placenta and attach to the fetal red blood cells, leading to their destruction. When a DAT is performed in cases of HDFN, it will be positive because these antibodies are present on the surface of the red blood cells.

Transfusion reactions can also lead to a positive DAT, particularly when there are antibody-mediated reactions following an incompatible blood transfusion. However, without specific context regarding the patient's history or the timing of the transfusion, this condition is less definitive than HDFN for a clear expected positive result.

Autoimmune hemolytic anemia is another condition that can result in a positive DAT, as the body's immune system mistakenly attacks its own red blood cells. The antibodies involved in this process would also be detected by the test.

Chronic lymphocytic leukemia,