Acute Hemolytic Anemia

Today we discussed a case of acute hemolytic anemia, following a viral syndrome. The typical patient with acute hemolytic anemia presents in a somewhat nonspecific way, and the final diagnosis is not often met until an exhaustive (if somewhat algorithmic) laboratory workup has been completed. Usually, the initial presentation is simply for fatigue with exercise or dyspnea with exercise. Patients may complain of yellowed skin or abnormally dark urine. Exam will variably reveal jaundice, splenomegaly, or resting tachycardia depending on the extent and acuity of the anemia.

1. What is the laboratory workup for a suspected hemolytic anemia? While specific tests are driven by the history and physical exam, after an anemia is confirmed by a complete blood count, there are features which can be suggestive of hemolytic anemia, though no single test is sufficient to diagnose it. An elevated reticulocyte count (in the absence of another cause) points toward a hemolytic mechanism. An elevated LDH, low haptoglobin, and elevated unconjugated bilirubin are all suggestive. A positive coomb's test is also suggestive and points in the direction of immune mediated mechanisms. A smear with schistocytes and/or spherocytes points in the direction of hemolysis as well. 

2. What are the causes of hemolytic anemia? This can be subdivided by where the defect lies and where the hemolysis itself occurs. The most important/urgent causes are those that can lead to death quickly, including thrombotic microangiopathies (TTP/HUS/DIC), pathogen mediated hemolysis, and transfusion related hemolysis.