Sections View Full Chapter Figures Tables Videos Full Chapter Figures Tables Videos Supplementary Content ++ Key Features ++ Essentials of Diagnosis ++ Irreversibly sickled cells on peripheral blood smear Positive family history and lifelong personal history of hemolytic anemia Recurrent pain episodes Hemoglobin S is the major hemoglobin seen on electrophoresis ++ General Considerations ++ Autosomal recessive disorder in which abnormal hemoglobin leads to chronic hemolytic anemia with numerous clinical consequences Single DNA base change leads to amino acid substitution of valine for glutamine in the sixth position on β-globin chain Sickling is caused by increased red blood cell (RBC) hemoglobin S concentration, RBC dehydration, acidosis, and hypoxemia Acute painful episodes occur as a result of vaso-occlusion by sickled RBCs occur spontaneously or they are provoked by infection, dehydration, or hypoxia Sickling is retarded markedly by hemoglobin F; high hemoglobin F levels are associated with more benign course Patients with S-β+-thalassemia and SS α-thalassemia also have a benign clinical course Patients with heterozygous genotype (hemoglobin AS) have sickle cell trait ++ Demographics ++ βS gene is carried in 8% of American blacks Sickle cell anemia occurs in 1 birth in 400 in American blacks Onset during first year of life, when hemoglobin F levels fall ++ Clinical Findings ++ Symptoms and Signs ++ Chronic hemolytic anemia produces Jaundice Pigment (calcium bilirubinate) gallstones Splenomegaly (early in life) Poorly healing ulcers over the lower tibia Anemia may be life-threatening during Hemolytic or aplastic crises Infection caused by immunoincompetence from hyposplenism Hemolytic crises result from splenic sequestration of sickled cells (primarily in childhood, before spleen has infarcted) or with coexistent disorders such as glucose-6-phosphate dehydrogenase deficiency Aplastic crises occur when bone marrow compensation is reduced by infection or folate deficiency Acute painful episodes Include spine, long appendicular, and thoracic bones Can last hours to days and produce low-grade fever Acute vaso-occlusion may cause priapism and strokes Repeated vaso-occlusion affects Heart (cardiomegaly, hyperdynamic precordium, systolic murmurs) Lungs Liver Bone (ischemic necrosis, staphylococcal or salmonella osteomyelitis) Spleen (infarction, asplenia) Kidney (infarction of renal medullary papillae, renal tubular concentrating defects, and gross hematuria) Acute chest syndrome Characterized by acute chest pain, hypoxemia and pulmonary infiltrates on a chest radiograph Must be distinguished from an infectious pneumonia Pulmonary hypertension is associated with decreased survival Increased susceptibility to infection occurs as a result of hyposplenism and complement defects Sickle cell trait Asymptomatic most often Acute vaso-occlusion occurs only under extreme conditions Gross hematuria or renal tubular defect causing inability to concentrate urine may occur ++ Differential Diagnosis ++ Other sickle cell syndromes Sickle cell trait Sickle thalassemia Hemoglobin SC disease Osteomyelitis Hematuria from other cause Acute rheumatic fever ++ Diagnosis ++ Laboratory Tests ++ Hematocrit usually 20–30% Peripheral blood smear: irreversibly sickled cells comprise 5–50% of RBCs; reticulocytosis (10–25%); nucleated RBCs; Howell-Jolly bodies and target cells White blood cell count ... GET ACCESS TO THIS RESOURCE Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth Get Free Access Through Your Institution Contact your institution's library to ask if they subscribe to McGraw-Hill Medical Products. Access My Subscription GET ACCESS TO THIS RESOURCE Subscription Options Pay Per View Timed Access to all of AccessMedicine 24 Hour $34.95 (USD) Buy Now 48 Hour $54.95 (USD) Buy Now Best Value AccessMedicine Full Site: One-Year Individual Subscription $995 USD Buy Now View All Subscription Options