hematology and oncology
Overview of Hemolytic Anemia
Diagnosis of Hemolytic Anemia
Peripheral smear and reticulocyte count Serum bilirubin, lactic dehydrogenase (LDH), haptoglobin, and alanine aminotransferase (ALT) Antiglobulin (Coombs) test and/or hemoglobinopathy screen Hemolysis is suspected in patients with anemia and reticulocytosis. If hemolysis is suspected, a peripheral smear is examined and serum bilirubin, LDH, haptoglobin, and ALT are measured. The peripheral smear and reticulocyte count are the most important tests to diagnose hemolysis. Antiglobulin testing or hemoglobinopathy screening (eg, high-performance liquid chromatography [HPLC]) can help identify the cause of hemolysis. However, in some patients with an Autoimmune Hemolytic Anemia the reticulocyte count fails to increase, which creates a hematologic emergency necessitating prompt transfusion therapy. Abnormalities of RBC morphology often suggest the presence and cause of hemolysis (see table Red Blood Cell Morphologic Changes in Hemolytic Anemias ). The presence of spherocytes on the peripheral smear suggests an extravascular cause of hemolysis such as Intravascular hemolysis is suggested by RBC fragments (schistocytes) on the peripheral smear and by decreased serum haptoglobin levels; however, haptoglobin levels can decrease because of hepatocellular dysfunction and can increase because of systemic inflammation. Intravascular hemolysis is also suggested by urinary hemosiderin. Urinary hemoglobin, like hematuria and myoglobinuria, produces a positive benzidine reaction on dipstick testing; it can be differentiated from hematuria by the absence of RBCs on microscopic urine examination. Free hemoglobin may make plasma reddish brown, noticeable often in centrifuged blood; myoglobin does not. Once hemolysis has been identified, the etiology is sought. To narrow the differential diagnosis in hemolytic anemias Consider risk factors (eg, geographic location, genetics, underlying disorder) Examine the patient for splenomegaly Do a direct antiglobulin (direct Coombs) test Most hemolytic anemias cause abnormalities in one of these variables, and so test results can direct further testing. Other laboratory tests that can help discern the causes of hemolysis include the following: Quantitative hemoglobin electrophoresis RBC enzyme assays Flow cytometry Cold agglutinins Osmotic fragility The direct Coombs test is used to determine whether red blood cell (RBC)-binding antibody (IgG) or complement (C3) is present on RBC membranes. The patient's RBCs are incubated with antibodies to human IgG and C3. If IgG or C3 is bound to RBC membranes, agglutination occurs–a positive result. A positive result suggests the presence of autoantibodies to the patient's RBCs. If the patient has received a transfusion in the last 3 months, a positive result could also represent alloantibodies to transfused RBCs (usually occurring in acute or delayed hemolytic reaction). The indirect Coombs test is used to detect IgG antibodies against red blood cells (RBCs) in a patient's serum. The patient's serum is incubated with reagent RBCs; then Coombs serum (antibodies to human IgG, or human anti-IgG) is added. If agglutination occurs, IgG antibodies (autoantibodies or alloantibodies) against RBCs are present. This test is also used to determine the specificity of an alloantibody. 