Autoimmune hematologic disorders (PEARLS)
| Autoimmune Hemolytic anemia |
Increased destruction of erythrocytes due to the presence of anti-erythrocyte autoantibodies (AEA)
↓ Hemoglobin/hematocrit, ↑ Retic, ↑ LDH, ↓ Haptoglobin,↑ Bilirubin (indirect), and + Direct Coombs Test
Some people have no symptoms, and other people are tired, short of breath, and pale
- Severe disease may cause jaundice or abdominal discomfort and fullness due to splenomegaly
Treated with corticosteroids
- In refractory cases immune globulin or splenectomy
Common in all hemolytic anemias: • Elevated reticulocyte count, LDH • Decreased haptoglobin and hemoglobin/ hematocrit
- LDH level is elevated—LDH is released when RBCs are destroyed
- Elevated indirect (unconjugated) bilirubin levels due to degradation of heme because RBCs are destroyed
- Haptoglobin levels—low in hemolytic anemias (especially intravascular hemolysis). Haptoglobin binds to hemoglobin, so its absence means that hemoglobin was destroyed
- Elevated reticulocyte count due to increased RBC production
Common to autoimmune anemia:
- Direct Coombs test (detects antibody or complement on RBC membrane)—positive in autoimmune hemolytic anemia (AIHA)
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| Immune Thrombocytopenic Purpura (ITP) |
ITP results from autoimmune antibody formation against host platelets
CBC normal except ↓ low platelets (<20,000) and + Direct Coombs Test
In children, it may follow a viral infection. In adults, it may be chronic
- Acute form • Seen in children • Preceded by a viral infection (in most cases) • Usually self-limited—80% resolve spontaneously within 6 months
- Chronic form • Usually seen in adults, most commonly in women between 20 and 40 years of age • Spontaneous remissions are rare
Symptoms may include easy bruising, bleeding, and petechiae (pinpoint-sized reddish-purple spots) on the lower legs
Treated with corticosteroids
- In children, ITP usually resolves without treatment
- IV immune globulin—saturates the reticuloendothelial system binding sites for platelet-bound self-immunoglobulin, so there is less platelet uptake and destruction by the spleen
- Splenectomy—induces remission in 70% to 80% of the cases of chronic ITP
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| Pernicious anemia |
Pernicious anemia is caused by an autoantibody formation against intrinsic factor
Megaloblastic anemia (↑ MCV > 100), hypersegmented Neutrophils + schilling test ↓ intrinsic factor and parietal cell antibodies
- Symptoms include fatigue and weakness
- Untreated pernicious anemia can cause heart and nerve damage
Parenteral therapy is preferred—cyanocobalamin (vitamin B12) IM once per month
Schilling test—historically used to determine if B12 deficiency is due to pernicious anemia. Not routinely used now.
- Give an IM dose of unlabeled vitamin B12 to saturate binding sites
- Give an oral dose of radioactive vitamin B12; measure the amount of vitamin B12 in urine and plasma to determine how much vitamin B12 was absorbed
- Repeat the test (oral radioactive vitamin B12) with the addition of intrinsic factor. If malabsorption is the problem, adding intrinsic factor will not do anything. However, if pernicious anemia is present, adding intrinsic factor will improve serum vitamin B12 levels
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