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Background: In Ontario, Canada's largest province, population-based health administrative data represents an accessible and useful tool for population surveillance of people with chronic diseases. While hemoglobinopathies can be identified using data from universal hemoglobinopathy screening, which was implemented in November 2006, these data would not contain information on affected immigrants (21.9% of the population). We validated algorithms using provincial health administrative data and newborn screening data to identify children with hemoglobinopathies whether or not they were born in Ontario, thereby creating a population-based surveillance cohort. Objectives: (1) Validate algorithms to identify children with sickle cell disease, thalassemia and other hemoglobinopathies from within health administrative data; and (2) Determine incidence and prevalence of hemoglobinopathies in Ontario children. Methods: For the validation study, a positive reference cohort was established using lists of known hemoglobinopathy patients who were followed at five pediatric hemoglobinopathy treatment sites in Ontario and born between November 24, 2006 and March 31, 2013. Health card numbers of these patients were linked deterministically to unique identification numbers in administrative data, which included data on hospitalizations, physician claims, sociodemographic characteristics, immigration records and cause of death. The negative reference cohort included all children residing in Ontario cities who had never been seen at a hemoglobinopathy centre, and therefore assumed not to have disease. Various combinations of administrative data codes were tested for their ability to identify children <18 years of age with hemoglobinopathies from within the databases, and we selected the algorithms with the highest positive predictive value, while maintaining sensitivity >80%. Using two validated algorithms, we identified all children with hemoglobinopathies born between April 1, 1991 and March 31, 2013. We described the crude incidence and prevalence per 100,000 patient-years (PYs). Results: Two algorithms functioned best to identify incident and prevalent hemoglobinopathy cases (see Table). Among children born between April 1, 1991 to March 31, 2013, 1526 incident hemoglobinopathy patients were identified using Algorithm 1 (crude incidence of 4.85 per 100,000 PYs) and 1660 new hemoglobinopathy patients were identified using Algorithm 2 (crude incidence 5.28 per 100,000 PYs, 95% CI 3.51 to 3.92). In 2013, the overall prevalence of children <18 years living with hemoglobinopathies was 1215-1325 cases. Conclusion: Through an innovative approach using provincial health administrative, immigration and demographic data, this study identified a rising incidence and prevalence of hemoglobinopathies among Ontario children <18 years of age between April 1, 1991 and March 31, 2013, potentially due to increased immigration rates. These findings could be used to inform health services distribution. This surveillance cohort will be used to understand the impact of immigration status on health care inequality for hemoglobinopathy-related health services delivery, as well as to assess outcomes in this important group of chronic diseases. Disclosures Klaassen: Amgen Inc.: Membership on an entity's Board of Directors or advisory committees; Octapharma AG: Consultancy, Honoraria; Agios Pharmaceuticals Inc.: Consultancy; Novartis: Research Funding; Hoffman-La Roche: Consultancy; Shire: Consultancy; Cangene: Research Funding. Jardine:Pfizer: Other: Advisory board; Bayer: Other: Advisory board; Baxalta: Other: Advisory board.

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Background: Since hydroxyurea emerged as an effective therapy for sickle cell disease (SCD), there have been numerous studies that have demonstrated its safety and efficacy in children and adults with SCD. In their 2014 guidelines, the NHLBI recommended that hydroxyurea treatment should be offered to all infants and children with sickle cell anemia (HbSS and HbS/beta0 thalassemia) starting at 9 months of age. However, hydroxyurea is underused among children and adolescents with SCD and to date, there have been no studies that have identified the specific determinants that may predict hydroxyurea adherence in these patients. Objectives: 1. To identify predictors of hydroxyurea adherence in children with SCD. 2. To measure the rate of hydroxyurea use among CHEO patients with SCD who were born between January 1, 2003 and December 31, 2015; and 3. To compare the rates of SCD-related complications between patients who were not prescribed hydroxyurea, patients who were adherent to hydroxyurea and patients who were not adherent to hydroxyurea Methods: We extracted medical chart data to identify patients with SCD who were born between January 1, 2003 and December 31, 2015. Patients were classified as either "Not prescribed hydroxyurea" or "Prescribed hydroxyurea" based on clinical documentation and the presence of at least one hydroxyurea outpatient prescription. For those patients who were prescribed hydroxyurea, hematological indices were collected and analyzed over time to estimate adherence to hydroxyurea. To measure the adherence of children prescribed hydroxyurea, we examined the trends in the patient's hematological indices after their first prescription of hydroxyurea. Adherence was defined as increased hematological indices (from baseline) by greater than or equal to any 2 of the following: Mean corpuscular volume (MCV) by 10 fL; Hemoglobin levels (g/L) by 10 g/L and/or %HbF (fetal hemoglobin) by 10%. We measured the frequency of disease-related complications among CHEO patients with SCD according to their use of hydroxyurea and used multivariate analyses to evaluate immigration status, newborn screening status, SCD subtype, SCD complications, income, age and sex as predictors for hydroxyurea adherence. Results: Children with HbSS were more likely to have been prescribed hydroxyurea compared to children with HbSC (87.8% vs. 9.5%). Canadian citizenship, newborn hemoglobinopathy screening and lower familial income were associated with better hydroxyurea adherence (Table 1). Although the association was not statistically significant, patients were more likely to be prescribed hydroxyurea if they were from a lower income background (61.9% for lowest and second lowest quartiles vs. 38.1% for third and highest quintiles). Patients were also more likely to adhere to hydroxyurea if they did not have private medical insurance for hydroxyurea coverage (Table 1). Finally, hydroxyurea adherence was associated with reduced rates of health care utilization and SCD-related complications (Table 2). Conclusions: In line with previous studies of hydroxyurea for the treatment of SCD, patients who were adherent to hydroxyurea had fewer complications compared to those patients who were either non-adherent to or not prescribed hydroxyurea. Similarly, patients had fewer complications after being prescribed hydroxyurea compared to before they started hydroxyurea with a reduction in the rate of ED visits, acute chest syndromes, complications, transfusions and hospitalizations. Patients from non-immigrant families, patients who were identified through newborn hemoglobinopathy screening and patients from lower income families were more likely to be adherent to hydroxyurea. Although the results of this study were limited by its small sample size, further studies will clarify these determinants of hydroxyurea adherence among SCD patients and enable clinicians to improve hydroxyurea adherence for SCD patients. Disclosures Klaassen: Shire: Consultancy; Novartis: Research Funding; Hoffman-La Roche: Consultancy; Amgen Inc.: Membership on an entity's Board of Directors or advisory committees; Octapharma AG: Consultancy, Honoraria; Agios Pharmaceuticals Inc.: Consultancy; Cangene: Research Funding.