Asthma Is Associated with Mortality in Children with Sickle Cell Anemia

Background: Acute chest syndrome (ACS) is one of the leading causes of premature death among people with sickle cell anemia (SCA). Children with SCA and asthma have an increased risk of ACS (Boyd et al, Pediatric Pulmonology, 2004). The Cooperative Study of Sickle Cell Disease (CSSCD) has previously reported the median age at death to be approximately 45 years, 42 years for males and 48 years for females (Platt et al, New England Journal of Medicine, 1994). The objective of this study is to determine if asthma in patients with SCA is associated with mortality. Methods: The cohort was comprised of African American participants with SCA anemia enrolled in the CSSCD from birth to 66 years of age who were followed beyond five years and were evaluated for asthma. Patients who died before age 5 years were not included in the cohort. Asthma was classified by physician diagnosis, documentation of an acute asthma event, and/or record of use of prescribed asthma medication. Mortality was determined for patients with and without asthma. Cox regression analysis included the following established risk factors for death (Platt et al, 1994): covariates age, white blood cell count level, renal failure, hemoglobin F level, seizure, and acute chest syndrome. Results: A total of 1963 African American individuals with SCA were classifiable for asthma, enrolled in the study and followed for a total of 18,496 patient-years. The average age at study entry was 13.9 years, and the mean length of follow-up was 9.4 years. A total of 138 individuals (7.0%) had asthma; 70% were classified by a physician diagnosis, 10% by documentation of an acute asthma event, and 20% by record of using a prescribed asthma medication. Individuals with asthma had a median lifespan of 52.5 years in comparison to 64.3 years and over a two-fold higher risk of mortality after controlling for age, white blood cell count, renal failure, hemoglobin F level, seizure, and acute chest syndrome rate (hazard ratio 2.36 by Cox regression, 95% CI 1.21 to 4.62, p=0.01). Conclusion: Asthma was associated with a significant increase in the risk of all-cause mortality among patients with SCA who lived to 5 years of age. In addition to previously identified risk factors, asthma is an independent predictor of mortality.