SICKLE CELL DISEASE

Valerie Cachat

Overview

Sickle cell disease (SCD) is a group of chronic genetic disorders that affect an estimated 70,000 to 100,000 Americans (National Heart, Lung, and Blood Institute, 2014). SCD is characterized by an abnormal hemoglobin, called hemoglobin S (HbS) or sickle hemoglobin, in the red blood cells (RBCs). The most common form of SCD is homozygous (SS) allele. Other variants are the result of compound heterozygotes for HbS and other β-globin variants, including sickle cell (SC), Sβ⁺ thalassemia, and Sβ⁰ thalassemia. Patients with SCD are at high risk for acute and chronic complications that may result in disability or death.

Background

SCD is a group of inherited hemoglobinopathies associated with hemolytic anemia and vaso-occlusion complications. All forms of SCD are inherited in an autosomal recessive pattern. Normally, two β-globin chains combine with two α-globin chains to form the predominant normal Hb in adults (HBA). SCD involves a mutation in the β-globin genes. An amino acid substitution of valine from glutamic acid occurs (Piccone, 2011). In deoxygenated conditions, the polymerization of HbS results in the characteristic sickle shape of the red blood cells. These sickled cells are stiff and adhere to one another and the vasculature leading to occlusion of the microvasculature and cause decreased oxygen delivery to tissues. This impaired oxygen delivery affects multiple organ systems. Organ damage occurs because of the sickling of the RBCs and chronic hemolysis throughout the life span (Ware, 2010). Affected children in the United States now increasingly survive into adulthood because of increased knowledge and advances in disease therapy; however, the average life span remains 20 to 30 years less from those individuals without SCD (National Heart Lung and Blood Institute, n.d.). Although the life span has increased, SCD continues to cause significant morbidity and mortality. Acute complications such as sudden anemia, vaso-occlusive pain crisis (VOC), splenic sequestration, acute chest syndrome (ACS), and stroke occur. In addition, chronic hemolysis affects all organ systems and can lead to kidney, liver, and cardiac decompensation among other complications.

Clinical Aspects

SCD is now diagnosed based on newborn screen in the United States. Early diagnosis has led to a decrease in complications, in particular, the risk of sepsis. Patients with SCD have functional asplenia. Shortly after birth, they are diagnosed with SCD and antibiotic prophylaxis is started to decrease the risk of sepsis because of encapsulated organisms (Streptococcus pneumoniae in particular). Febrile illness in a patient with SCD is considered an emergency owing to the risk of bacterial 103sepsis. Fever may be the result of acute and sometimes life-threatening conditions such as ACS and osteomyelitis. Often, the cause of a fever is not clear. Patients with fever require evaluation including history and physical, complete blood count (CBC) with differential, reticulocyte count, blood culture, and urine culture when urinary tract infection is suspected. Patients presenting with respiratory symptoms or chest pain should have a chest radiograph done to rule out developing ACS. Prompt administration of empiric parenteral antibiotics with coverage for S. pneumoniae is necessary. Patients who appear ill should be hospitalized for observation and continued antibiotic administration, and intravenous fluids. Close attention should be paid to additional symptoms concerning the development of ACS including hypoxia, tachypnea, fever, increased work of breathing and osteomyelitis, including localized pain, fever, swelling, and erythema (Piccone, 2011).

ASSESSMENT

Pain is perhaps the hallmark of sickle cell disease, with both acute and chronic pain being a significant cause of morbidity. Occlusion of the microvasculature leads to poor perfusion causing hypoxia, ischemia, and ultimately, tissue damage (Ballas et al., 2012

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