Sickle Cell DiseaseCore Concepts for the
Emergency Physician and Nurse
Epidemiology, Genetics, PathophysiologySpring 2013
Paula Tanabe, PhD, RN, FAEN, FAANAssociate Professor
Duke University, Schools of Nursing and Medicine
Epidemiology of SCD
• SCD is a genetic disease affecting 70,000 – 100,000
Americans, primarily of African descent (Hassell, 2010)
• Most common genetic disease among blacks
• SCD occurs in 1 of every 500 black births• 1:1,100 Hispanics (eastern states) • 1:32,000 Hispanics (western states)• SCD occurs in many other ethnic groups, including
Northern Europeans and those that live in the Middle Eastern Countries
• 1:12 African-Americans are carriers (trait) for the disorder
Changes in Life Expectancy
• National Center for Health Statistics (CDC)
• Compared 1999-2007 with 1979-1998
• Largest declines in ages 0-4
• Smaller but significant declines up to age 19
– Due to prophylactic treatment with penicillin and vaccinations
– Transcranial doppler screening identifies children at risk of
stroke; placed on chronic transfusion therapy to prevent stroke
• No differences in the 20-24 age group
• Increase in death rate ages: 45-54, 55-65, and 65-75
Normal Vs. Sickle Red Cells
Normal• Biconcave disc-shaped• Deformable• Life span of 120 days
Sickle• Sickle-shaped• Rigid • Live for 20 days or
less• Sticky surface,
abnormal properties
Prolonged Sickling of RBC’s
• After recurrent episodes of sickling–membrane damage
occurs– cells not capable of
resuming biconcave shape upon re-oxygenation
• Deformed sickle cells adhere to endothelium & macrophages– induces hemolytic
process
Hemolysis and Vaso-occlusion
Vaso-occlusion:• Complex process initiated
by rigid and abnormally shaped sickled RBC’s
• Abnormal adhesion occurs to the endothelium
• Activation of WBC’s, RBC’s and the endothelial surface which enhances the VOC process
• Results in tissue damage, hypoxia, necrosis and organ dysfunction
Hemolysis:
▪ Anemia in SCD is caused by red cell destruction, or hemolysis
▪ The degree of anemia varies widely between patients
▪ Red cell production by the bone marrow increases dramatically, but is unable to keep pace with the destruction
Chronic Manifestations:• Anemia• Jaundice• Splenomegaly• Functional asplenia• Cardiomegaly and functional
murmurs• Hyposthenuria and enuresis• Proteinemia• Cholelithiasis• Delayed growth and sexual
maturation• Restrictive lung disease*• Pulmonary hypertension*• Avascular necrosis• Proliferative retinopathy• Leg ulcers• Transfusional hemosiderosis*
Acute Manifestations:• Bacterial sepsis or
meningitis*• Recurrent vaso-occlusive
pain (dactylitis, musculo-skeletal or abdominal pain)
• Splenic sequestration*• Aplastic crisis*• Acute chest syndrome*• Stroke*• Priapism• Hematuria, including
papillary necrosis
Acute and Chronic Manifestations
*Potential cause of mortality
Sickle Cell Disease (SCD) Common Genotypes
Sickle cell anemia (SS, most severe form)
Sickle/Hb C disease (SC, lesser severity, but can still have pain episodes, and life-threatening complications)
Sickle/Beta plus thalassemia (Sβ+ thalassemia, similar to SC)
Sickle/Beta zero thalassemia(Sβ° thalassemia, similar to SS)
65 %
25 %
8 %
2 %
Genotype Approximate % of US Patients
References
• Hassell KL. Population estimates of sickle cell disease in the U.S. Am J Prev Med. 2010;38(4S):S512-S521.
• Platt et al. Mortality in sickle cell disease, life expectancy
and risk factors for early death. NEJM 1994. 330: 1639-44.• Hamideh, D. Trends in Mortality Among Patients with SCD
in the United States. Is there any change in the past 10 years? 2012. 6th Annual Sickle Cell Disease Research and Educational Symposium & Annual National SCD Scientific Meeting
• http://wonder.cdc.gov/controller/datarequest/D79
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