The Number of People with Sickle Cell Disease in the United States: National and Individual State Estimates.
Authors: Brousseau David C , Panepinto Julie A. , Nimmer Mark , Hoffmann Raymond G 
Published: October 2019

Abstract
Abstract 1365
Poster Board I-387

Background
Although sickle cell disease is a genetic disease diagnosed by state newborn screening programs, it is not a reportable condition. Therefore it is difficult to ascertain the actual number of affected individuals living with sickle cell disease in the United States. One NIH estimate puts the number between 50,000 and 75,000 while the Sickle Cell Disease Association of America estimates the number to be “over 70,000”. Without accurate estimates, clinicians, health services researchers, and policy makers are all working with incomplete information when determining the extent of the cost and health consequences of sickle cell disease. Our objective was to estimate the number of people with sickle cell disease for the United States as a whole and for each individual State, adjusting for the increased mortality of sickle cell disease.

Methods
Census estimates by age and race/ethnicity were obtained for both the United States as a whole and for each individual State from the US Census website. The prevalence of sickle cell disease for blacks was uniformly applied to the U.S. and individual states using a rate of 289 black children with sickle cell disease per 100,000 live births. Based on previously published prevalence rates for Hispanics, prevalence rates of 89.8 Hispanic children of non-Mexican ancestry with sickle cell disease per 100,000 live births and 3.14 Hispanic children of Mexican ancestry with sickle cell disease per 100,000 live births were calculated. We did not include sickle cell disease for whites or Asians in our estimate. Year 2005 was used as the baseline year for all calculations. Consistent with previous literature, at age 0, 60% of children with sickle cell disease were classified as having HgbSS/SB0 and 40% of children were classified as having HgbSC/SB+. These proportions were altered towards higher proportions of HbSC/SB+ with increasing age based on the increased mortality of the more severe forms of sickle cell disease. To adjust for mortality, we analyzed the data based on age and sickle cell type, and used published mortality data for different sickle cell genotypes to calculate survival of the population to a given age. A population multiplier was then used to adjust population estimates for the difference in population across age groups and differences in population patterns by race/ethnicity.

Results
Analysis revealed an estimate of 89,079 (95% CI: 88,494 – 89,664) people with sickle cell disease in the United States, of which 80,151 are black and 8,928 Hispanic. The South, with a sickle cell population of 47,354 people, comprised more than 53% of all people with sickle cell disease in the United States. The five states with the highest estimated number of people with sickle cell disease were New York with 8,308; Florida with 7,539; Texas with 6,765; California with 6,474; and Georgia with 5,890. These five states comprised more than 43% of the total sickle cell population for the nation. Finally, the increased mortality for HgbSS/SB0 leads to an alteration in the relative percentages of sickle cell genotypes, with HgbSS/SB0 comprising 60% of people with sickle cell disease at birth, half of the sickle cell population at slightly over 30 years old, and only 25% of the sickle cell population by 60 years old.

Conclusion
This study reveals that the sickle cell population in the United States is higher than previously reported, with almost 90,000 people with sickle cell disease. In addition, differential mortality increases the percentage of people with HbSC/SB+, such that after 40 years of age they represent the majority of the sickle cell population. The population estimates for the country as well as the individual states provide important information with regard to allocation of resources for this chronic disease which primarily affects lower income, underserved individuals.

Disclosures
No relevant conflicts of interest to declare.