LabMed

Autoimmune Hemolytic Anemias

At a Glance

Autoimmune hemolysis is an important component in the differential of acquired anemia. Hemolytic anemia should be considered in patients without an obvious cause of anemia (e.g., bleeding). Signs of autoimmune hemolysis may include scleral icterus and jaundice. Malignant diseases, such as lymphoma, and autoimmune diseases, such as lupus, may be associated with IgG ("warm") autoimmune hemolysis. Drugs, such as aldomet and fludarabine, are also associated with IgG ("warm") autoimmune hemolysis. Viral infections are associated with IgM ("cold agglutinin") autoimmune hemolysis.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

If a hemolytic anemia is in the differential, haptoglobin, lactate dehydrogenase (LDH), and bilirubin can be useful. Haptoglobin scavenges free hemoglobin and is low in hemolytic anemia.

Hemolysis may also lead to elevated LDH and bilirubin. LDH is present in red cells and hemolysis causes release into the plasma. Bilirubin is a breakdown product of hemolglobin and becomes elevated as hemoglobin is released. Indirect hyperbilirubinemia is typically seen in hemolysis.

To determine the potential autoimmune nature of the anemia, a type, screen, and direct antiglobulin test (DAT, direct Coomb's test) can be ordered. Antibody screens (and follow-up antibody identification panels) will typically show reactivity with all tested cells. This finding is almost always seen with IgG autoantibodies but will vary with IgM autoantibodies, depending on the test method. ABO typing discrepancies may be seen in patients with a cold agglutinin (e.g., front type as an A, but back type as an O). The DAT determines whether IgG antibody or complement (a surrogate for IgM) is binding the patient's red cells and is generally positive in autoimmune hemolytic anemia.

Review of the peripheral smear is also important. In warm autoimmune hemolysis, there may be spherocytes due to removal of part of the red cell membrane. In cold agglutinin disease, spontaneous agglutination may be seen on the smear. As there is generally no red cell production defect in hemolytic anemias, reticulocyte counts may be elevated.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Haptoglobin is very sensitive but not specific for autoimmune hemolysis, as even small amounts of free hemoglobin can deplete normal levels of serum haptoglobin. It may also be decreased in liver disease. As haptoglobin is an acute phase reactant, it may be elevated in a number of diseases leading to difficulties in interpretation.

LDH is present in all tissues, including red cells, so elevations are consistent with hemolysis but are very nonspecific as any cellular damage may affect levels. As such, there are many other disorders that may cause an elevated LDH.

Approximately 5-10% of DATs may be positive in hospitalized patients. Causes may include incompatible plasma transfusion (typically through platelet transfusion) and nonspecific binding of immunoglobulin and complement, as these are often elevated in hospitalized patients. Incompatible red cell transfusion can also cause a positive DAT.

An alloantibody to a high frequency antigen or multiple alloantibodies can cause a pan-reactive screen and antibody identification panels.

Some individuals may have evidence of autoantibodies, but they may not be clinically significant in regard to hemolysis. That is, the presence of a positive DAT and/or pan-reactivity on an antibody screen must be correlated with other signs and laboratory tests for hemolysis.

What Lab Results Are Absolutely Confirmatory?

There is no test that is absolutely confirmatory for autoimmune hemolytic anemia; however, in the setting of a DAT positive for IgG, the antibody can be eluted and run on an antibody identity panel. A pan-reactive eluate is consistent with warm autoimmune hemolytic anemia.

In the setting of a DAT positive for complement, a cold agglutinin identity panel can be performed. A specific identity for a cold agglutinin (e.g., anti-I, anti-i) and evidence of a high thermal amplitude is consistent with cold agglutinin disease but needs correlated with other clinical and laboratory findings.

What Confirmatory Tests Should I Request for My Clinical Dx? In addition, what follow-up tests might be useful?

In rare cases, the standard DAT may not be adequate to detect autoantibodies to red cells. If there is very high clinical suspicion for autoimmune hemolytic anemia with a negative DAT, more sensitive techniques can be used to determine whether there is antibody coating the patient's red cells. These include performing an eluate, use of enhancement reagents, flow cytometry, and detection of anti-IgA antibodies, which are sometimes, albeit rarely, implicated in hemolysis.

In rare cases, an autoantibody may have specificity usually in the Rh system. In this setting, the patient's red cells will phenotype as positive for the antigen. Recent transfusion may complicate interpretation of the phenotype data, and molecular testing may be useful to determine the true antigen status of the patient and, therefore, the allo- or auto-reactive nature of the antibody.

Table 1

Tests Results Indicative of the Disorder
Direct antiglobulin test (DAT) Antibody screen (and follow-up antibody identification panels) Indirect bilirubin Lactate dehydrogenase Haptoglobin
positive for IgG in warm autoimmune hemolytic anemia, positive for C3 in cold agglutinin disease pan-reactive in warm autoimmune hemolytic anemia and potentially in cold agglutinin disease elevated elevated decreased
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