Autoimmune hemolytic anemia laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-In-Chief: Prashanth Saddala M.B.B.S; Shyam Patel [2]
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Overview
Laboratory Findings
A variety of laboratory tests can be used to help diagnose autoimmune hemolytic anemia.
- Complete blood count: The complete blood count (CBC) will reveal decreased hemoglobin, typically less than 10 g/dl. By definition, autoimmune hemolytic anemia is characterized by anemia. In some cases, patients can also have a low platelet count (thrombocytopenia), such as in the case of Evan's syndrome, which is a syndrome of autoimmune hemolytic anemia plus immune thrombocytopenia purpura (ITP). The white blood cell count is normal in autoimmune hemolytic anemia, unless a patient is receiving treatment with corticosteroids, which can cause leukocytosis, or elevated white blood cell count.
- Coombs' test: This is also known at the direct antiglobulin test. The Coombs' test assesses for the presence of antibodies attached to a patient's red blood cells, which is a key feature of autoimmune hemolytic anemia. The test is performed by collecting peripheral blood containing red blood cells, which presumably harbor antibodies in their surfaces, then adding in a Coombs' reagent and assessing for agglutination. If agglutination occurs in the presence of the Coomb's reagent, this indicates the presence of antibodies on the surface of red blood cells. Of note, the Coombs' test can be negative in 3-10% of patients.[1] The reasons for a negative Coombs' test include inability to detect a minimal amount of immunoglobulin G (IgG) on the red blood cell surface. Another reason for a false-negative Coombs' test is the presence of immunoglobulin A (IgA) on the red blood cell surface, instead of IgG.
- Indirect anti-globulin test: This is also known as the indirect Coombs' test. The indirect anti-globulin test involves detection of circulating anti-red blood cell antibodies. The test involves using reagent red blood cell, which are commercially available, and adding the patient's serum (which presumably contains the anti-red blood cell antibodies. Then, the Coombs's reagent is added, and agglutination is observed.
- Hemoglobin in the urine: Elevated urine hemosiderin indicates intravascular hemolysis.
- Reticulocyte count: Patients with autoimmune hemolytic anemia will mount a compensatory response to red blood cell destruction by increasing erythroid production from the bone marrow. The immediate precursor to mature red bloods cells is the reticulocyte. An elevated reticulocyte count is an indication of active hemolysis.
- Serum bilirubin: Bilirubin is a breakdown product of biliverdin, which is a breakdown product of heme, which is found in hemoglobin. Upon red blood cell destruction in autoimmune hemolytic anemia, free heme is released into the circulation and is eventually broken down to bilirubin. An elevated total bilirubin and indirect (unconjugated) bilirubin is an indication of hemolysis. Patients with autoimmune hemolytic anemia typically have total bilirubin level greater than 1 g/dl and indirect bilirubin of 50% or greater of the total bilirubin level.
- Serum haptoglobin: Bilirubin binds to haptoglobin, and therefore haptoglobin decreases in autoimmune hemolytic anemia. The level is typically less than 8 mg/dl in patients with active hemolytic anemia.
- Serum LDH: Lactate dehydrogenase (LDH) is an intracellular enzyme in red blood cells and is released upon destruction of red blood cells. Patients with autoimmune hemolytic anemia have elevated LDH (typically greater than 300 units per liter). However, this test has low specificity, as LDH can be elevated in other conditions such as tumor lysis syndrome or ventricular assist device thrombosis.
References
- ↑ Berentsen S, Sundic T (2015). "Red blood cell destruction in autoimmune hemolytic anemia: role of complement and potential new targets for therapy". Biomed Res Int. 2015: 363278. doi:10.1155/2015/363278. PMC 4326213. PMID 25705656.