Discussion
To date this is the largest study looking at weight status in children and adolescence with SCD. Mississippi currently has the highest incidence of patients with sickle cell disease and also has the highest pediatric and adult obesity rates in the nation at 25.4% and 39.5% respectively(14, 15). In our sample, patients were more likely to be overweight/obese (24.5%) versus underweight (4.4%). Our sample of pediatric patients with SCD had a similar prevalence rate of overweight as both state and national prevalence rates. Additionally, the combined overweight/obesity rate for the current sample (24.5%) is comparable to other published national overweight/obesity rates ranging from 22-25% (15). Higher hemoglobin levels and lower absolute reticulocyte count were significantly associated with a higher BMI.
Historically, poor growth, short stature, and being underweight have been a concern in patients with SCD. Children with SCD are known to have higher resting energy expenditure compared to control children and this in part is associated with chronic anemia. Hemoglobin levels are highly correlated (r = 0.7) with resting energy expenditure(4, 16). Our current study found a significant relationship between increased hemoglobin levels and increased BMI which is consistent with past studies looking at improved growth in SCD. The Stroke Prevention Trial showed that children with SCD who were chronically transfused to maintain a hematocrit greater than 30% had significant improvement in height, weight and BMI z-scores such that after 2 years of treatment, they were of comparable size to their healthy peers(16). While we hypothesized that hydroxyruea and chronic transfusion therapy would be associated with increased BMI, current results did not support this hypothesis. These relationships may be too complex to capture in cross-sectional data, as patients on hydroxyruea and chronic transfusion therapy tend to have the most severe disease and medical compliance, or lack thereof, may impact results.
Overweight and obesity in otherwise healthy children is associated with medical complications such as hypertension, dyslipidemia, insulin resistance, dysglycemia, fatty liver disease and psychosocial complications (17). Metabolic syndrome, which includes: increased waist circumference, elevated triglycerides and fasting glucose and elevated blood pressure is a key-risk factor for cardiovascular disease(16). Prospective studies are needed that evaluate the consequence of overweight and obesity on the health of pediatric patients with SCD. It will be important to gauge the impact of elevated BMI on both morbidity and mortality in SCD as medical interventions continue to improve for SCD. This may ultimately impact guidelines for screening, as well as nutrition and exercise guidelines for these patients.
Although this study has the strength of having a large sample size (N = 781) and robust measurement of disease-related variables, several limitations warrant discussion. The primary limitation is being a retrospective cross-sectional chart review study. This type of data has inherent limitations as it exists for clinical purposes and random error in the data must be assumed. Additionally, a causal relationship between increased hemoglobin and decreased absolute reticulocyte count with increased weight status cannot be concluded with retrospective data. Further, this sample is limited to pediatric patients with SCD in Mississippi. BMI is strongly associated with genetic and environmental factors such as individual and family diet and exercise patterns(18). While current study results are similar to Chawla et al., (2013), these results may not generalize to other pediatric patients with SCD across the United States.