Anemias Associated With Increased Erythropoiesis

GENERAL PRINCIPLES

Definition

Anemias associated with increased erythropoiesis (i.e., an elevated reticulocyte count) are caused by bleeding or hemolysis and may exceed the capacity of normal BM to correct the Hgb.

Etiology

• Blood loss. If no obvious source, suspect occult loss into GI tract, retroperitoneum, thorax, or deep compartments of thigh depending on history (recent instrumentation, trauma, hip fracture, coagulopathy).

• Hemolysis can be categorized into two broad groups based on the cause of destruction: intrinsic (caused by deficits inherit to the RBC) and extrinsic (caused by factors external to the RBC).

î In general, intrinsic causes are inherited, whereas extrinsic causes tend to be acquired. Intrinsic disorders are a result of defects of the red cell membrane (i.e., hereditary spherocytosis), Hgb composition (i.e., sickle cell disease [SCD]), or enzyme deficiency (i.e., G6PD deficiency).

î Extrinsic disorders can result from antibodies (i.e., cold or warm reactive immunoglobulin), infectious agents (i.e., malaria), trauma, chemical agents (i.e., venom), or liver disease.

î Hemolytic disorders are also commonly categorized by the location of RBC destruction: intravascular (within the circulation) or extravascular (within the macrophage in the liver or spleen).

DIAGNOSIS

Laboratory findings of patients with suspected hemolysis typically include:

• Normocytic or macrocytic anemia with an elevated reticulocyte count.

• Elevated LDH and indirect hyperbilirubinemia reflect increased RBC turnover.

• Decreased haptoglobin due to binding of intravascular Hgb.

• The direct Coombs test (direct antiglobulin testing [DAT]) is an indicator of the presence of antibodies or complement bound to RBC.

• The indirect Coombs test indicates the presence of antibody in the plasma.

• A peripheral blood smear is essential and can aid in determining the etiology of hemolysis. Intravascular hemolysis may reveal red cell fragmentation (i.e., schistocytes, helmet cells), whereas spherocytes often occur in extravascular hemolysis. Polychromasia and nucleated RBCs are indicators of increased erythropoiesis.