Final answer:
The crucial test for diagnosing suspected autoimmune hemolytic anemia is the Direct Antiglobulin Test (DAT or Coombs' test), which detects antibodies bound to red blood cells.
Step-by-step explanation:
The most important finding in the diagnostic investigation of suspected autoimmune hemolytic anemia is the direct detection of antibodies attached to red blood cells in the patient's blood. A Direct Antiglobulin Test (DAT), commonly known as the Coombs' test, is crucial for diagnosing this condition. The test specifically looks for antibodies and complement proteins bound to the surface of red blood cells, which are indicative of an immune-mediated hemolysis.
In autoimmune hemolytic anemia, the immune system mistakenly produces antibodies that target and damage the patient's own red blood cells, leading to their premature destruction. Additional diagnostic tests may include a complete blood count (CBC) to check for anemia, a reticulocyte count to assess bone marrow response, and an indirect Coombs' test to detect free circulating antibodies in the patient's serum.
Apart from the Direct Antiglobulin Test, other relevant tests could include assays for antinuclear antibodies (ANA) which can indicate the presence of systemic autoimmune diseases like systemic lupus erythematosus (SLE), and may be associated with hemolytic anemia.