Hemoglobinopathies Pallor may result from the low hemoglobin level found in patients with sickle cell anemia and related hemoglobinopathies Acute accentuation of pallor can result from an aplastic crisis, a complication of hemolytic disorders that is particularly common in sickle cell anemia During an aplastic crisis, the normally elevated reticulocyte count may fall to zero, and the hemoglobin level may fall as low as to g/dL, resulting in severe pallor and signs of high-output cardiac failure The sequestration crisis of sickle cell anemia (HbSS) and related hemoglobin disorders (SC disease, S-β0–thalassemia, S-β+ –thalassemia) is a true hematologic emergency The presence of increased pallor and acute enlargement of the spleen in a patient with a sickling disorder should prompt immediate investigation of possible sequestration crisis The condition results from pooling of red cells and plasma in the spleen resulting in sudden and severe anemia with associated hypovolemia Emergent intervention is warranted as untreated cases may rapidly lead to death Although this complication rarely occurs in children with homozygous SCD or S-β0–thalassemia after the age of 5, sequestration crises may occur much later in children with sickling disorders such as SC disease or Sβ+ –thalassemia, in which early splenic infarction is less common Immune Hemolytic Anemia Pallor caused by autoimmune hemolytic anemia is usually acute in onset and may be associated with severe anemia Symptoms may include jaundice, dark urine, splenomegaly, and cardiovascular derangement The presence of only moderate anemia (6 to g/dL) at diagnosis should not detract from consideration of this disease as a hematologic emergency because brisk hemolysis may result in a sudden, additional fall in hemoglobin level Autoimmune hemolytic anemia is usually, but not always, characterized by a positive direct antiglobulin (Coombs) test and an increased reticulocyte count Spherocytes are commonly seen in the peripheral smear Other causes of immune hemolytic anemia include infections, drug exposure, inflammatory diseases, and malignancies Microangiopathic Anemia Alterations in the normal laminar flow of blood through the vascular system may cause increased red cell destruction In DIC, abnormal fibrin deposition within small blood vessels results in mechanical injury to the erythrocytes Thrombocytopenia and clotting abnormalities, which often herald the onset of DIC, may also contribute to the anemia via blood loss The main diagnostic findings are red cell fragments in the peripheral blood smear, with platelet and clotting abnormalities typical of a consumptive coagulopathy (see Chapter 93