Two criteria must be diagnose AIHA: serologic evidence of an autoantibody and clinical or laboratory evidence of hemolysis. Serologic evidence of an autoantibody is provided by positive autocontrol and direct antiglobulin test (DAT, direct Coombs´ test) results and subsequent identification of an autoantibody in the RBC eluate and possibly the serum. Serum reactivity with autologous RBCs generally indicates the presence of an autoantibody, but it does not exclude the presence of an autoantibody.
Hemolysis in AIHA can be either extravascular or intravascular. Tipically, intravascular hemolysis has a rapid and aggressive presentation, whereas extravascular hemolysis is milder. A CBC with peripheral smear, bilirubin, LDH (in particular isoenzyme 1), haptoglobin, and urine hemoglobin are basic tests used to evaluate and differentiate intravascular a extravascular hemolysis.
Suspected hemolysis; Many of the following findings:
- Rapid onset of pallor and anemia
- Jaundice with increased indirect bilirubin concentration
- History of pigmented (bilirubin) gallstones
- Presence of circulating spherocytic red cells
- Increased serum lactate dehydrogenase (LDH) concentration
- Reduced (or absent) level of serum haptoglobin
- A positive direct antiglobulin test (Coombs test)
- Increased reticulocyte percentage or absolute reticulocyte number, indicating the bone marrow’s response to the anemia
Confirmed hemolysis: The combination of an increased serum LDH and a reduced haptoglobin is 90 percent specific for diagnosis hemolysis, while the combination of a normal serum LDH and a serum haptoglobin >25 mg/dL is 92 percent sensitive for ruling out the presence of hemolysis.
- Abnormalities on the peripheral blood smear suggest extravascular hemolysis include: spherocytes, fragmented red cells, “bite” or blister cells, acanthocytes, and teardrop red cells.
- Abnormalities which suggest that the hemolysis is intravascular include the presence of free hemoglobin in plasma or urine, a urine sediment positive for iron (hemosiderinuria), and, in rare cases, the presence of circulating red cell “ghosts.”
- Gehrs BC, Friedberg RC. Autoimmune hemolytic anemia. Am J Hematol. 2002 Apr;69(4):258-71. [Medline]
- Dhaliwal G, Cornett PA, Tierney LM Jr. Hemolytic anemia. Am Fam Physician. 2004 Jun 1;69(11):2599-606. [Medline]
Created: Oct 25, 2009