Direct coombs test is positive in hemolytic anaemia due to –
**Core Concept**
In the context of hemolytic anemia, a positive direct Coombs test indicates the presence of autoantibodies or complement proteins that are bound to the surface of red blood cells, marking them for destruction. This phenomenon is a hallmark of autoimmune hemolytic anemia (AIHA).
**Why the Correct Answer is Right**
The direct Coombs test, also known as the antiglobulin test, detects the presence of antibodies or complement proteins that are attached to the surface of red blood cells. In AIHA, autoantibodies against red blood cell antigens (e.g., Rh, Kell, Duffy) are produced, leading to their opsonization and subsequent removal by the spleen. The direct Coombs test is a crucial diagnostic tool for identifying the underlying cause of hemolytic anemia.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the direct Coombs test result in hemolytic anemia.
* **Option B:** While complement activation plays a role in hemolytic anemia, it is not the primary reason for a positive direct Coombs test.
* **Option C:** This option is not directly related to the direct Coombs test in the context of hemolytic anemia.
**Clinical Pearl / High-Yield Fact**
A positive direct Coombs test in hemolytic anemia suggests an autoimmune etiology, which may respond to corticosteroids or other immunosuppressive therapies.
**Correct Answer:** A. Autoimmune hemolytic anemia (AIHA) due to autoantibodies against red blood cell antigens.