Changing Trends in Sickle Cell Disease-Related Mortality in the United States over Four Decades

Introduction: Sickle cell disease (SCD) causes significant morbidity and early mortality. The Cooperative Study of Sickle Cell Disease estimated median life expectancy for individuals with SCD at 42 years for males and 48 years for females in the early 1990s. However, this calculation was made prior to now standards-of-care in SCD, including routine transcranial doppler screening, pneumococcal prophylaxis, and the introduction of the primary disease-modifying therapy hydroxyurea and the widespread use of chronic blood transfusion. Over the last thirty years, with expanded access to disease modifying therapies, increased evidence exists for the preservation of organ function and less frequent acute vaso-occlusive pain. It remains unclear whether the introduction of these therapies has affected overall SCD-related mortality or the specific causes of death of those with SCD in the United States, particularly in the last decade when the use of hydroxyurea has expanded most significantly.

Methods: We used the US mortality statistics for 1979-2020 available publicly through the CDC WONDER database (http://wonder.cdc.gov), which is a compilation of county, state, and national-level mortality statistics derived from death certificates, including age category at death, sex, race, ethnicity, year of death, underlying cause of death, and additional contributing causes using ICD-9 codes for 1979-1998 (282.6 sickle cell anemia- all SCD genotypes were included under one code in ICD-9) and ICD-10 codes for 1999-2020 (D57.0 sickle cell anemia with crisis; D57.1 sickle cell anemia without crisis; D57.2 double heterozygous sickling disorders; D57.8 other sickle cell disorders). We searched the SCD ICD-10 codes listed as underlying cause of death by five-year age groups for Black individuals and all ethnicities, (from Hamideh and Alvarez, Pediatric Blood and Cancer 2013) and compared the crude death rates overall and for each age group to those of 1999-2009. We also searched using the SCD ICD-10 codes included in “the multiple causes of death” to determine the 15 most common ICD categories of death in each 10-year period.

Results: For the period 2010-2020, 5272 Black (Hispanic & non-Hispanic) individuals died in the United States with the underlying cause of death listed as one of the ICD-10 SCD codes (see Figure 1A for a map of the crude mortality rate distribution). The crude mortality rate was 1.1 per 100,000 Black individuals, which was significantly lower than the period 1999-2009 (crude rate 1.2 per 100,000, p < 0.0001) (Figure 1B). Of note, similar to prior trends, there is a significant increase in mortality rate in the 15-19 year age group versus 20-24 years (0.9 per 100,000 to 1.4 per 100,000, p < 0.0001) corresponding with the age of transition to adult centers. The mean age at death for all genotypes for 2010-2020 was 43 years (females: 44 years, males: 41 years) versus 39 years for 1999-2009 (females: 40 years, males: 38 years). For the period 2010-2020, 61% of cases listed SCD as the primary cause of death without specificity or proximal cause; for the other 39% of cases when an underlying cause of death was noted, cardiovascular disease was the most common (28%), followed by accidents (7%), cerebrovascular disease (7%), malignancy (6%), septicemia (4.8%), and renal disease (3.8%). The fifteen most common causes of death accounted for 90% of underlying causes of death listed in the SCD population.

Conclusion: The sickle cell disease-related mortality rate has significantly declined over the last 40 years, including in the period 1999-2020, corresponding with the introduction of disease modifying therapies, improved SCD care, and decreased infant mortality. This overall improvement, however, provides contrast to the enduring sharp increase in mortality in the young adult years. This demonstrates the critical need to improve the transition process from pediatric to adult care and to emphasize the need for additional support for young adults after they transition to adult SCD care.