Higher hydroxyurea adherence among young adults with sickle cell disease compared to children and adolescents

BACKGROUND: Sickle cell disease (SCD) results in severe complications, such as anaemia and pain episodes. Hydroxyurea (HU) is efficacious in SCD, yet adherence remains low. OBJECTIVE: To assess the relationship of HU adherence to health care utilization and patients’ characteristics. METHODS: This is a 5-year retrospective chart review. Patients’ demographics and medical history were collected from the electronic medical record (EMR). HU adherence was evaluated using foetal haemoglobin “HbF%”, mean corpuscular volume “MCV”, and absolute neutrophil count “ANC”. Age groups included children (<12 years), adolescents (12–17 years), and young adults (≥18 years). RESULTS: A total of 113 SCD patients on HU were included (median age 14 years, IQR 10–20; 50% female; 88% HbSS). Young adults had significantly higher HU adherence compared to adolescents and children, including higher median HbF% (24.2 vs. 12.4 vs. 8.6, p = .003), MCV (fl) (106.4 vs. 96.2 vs. 95.4, p = .01) and lower ANC (10(3)/ml) (3.25 vs. 4.9 vs. 4.2, p = .01), respectively. Patients with chronic pain had lower HU adherence (HbF% 15.3 vs. 10.7, p = .04; ANC 3.6 vs. 6.3, p = .002; MCV 102.3 vs. 93.1, p = .1). Patients with higher HbF or MCV and lower ANC had significantly less frequent emergency room visits (r(s)=–0.26, p = .01; r(s)=–0.23, p = .01; r(s)=0.24, p = .01) and hospitalizations (r(s)=–0.27, p = .01; r(s)=–0.31, p = .01; r(s)=0.21, p = .02) as well as shorter length of stays (r(s)=–0.27, p = .0045; r(s)=–.34, p = 0.004; r(s)=0.23, p = .02), respectively. Similar trends in HU adherence and health care utilization were seen in subgroup analysis of only HbSS patients. There was no significant association of HU adherence to patients’ sex, socio-economic status, distance from hospital, and HU duration. CONCLUSIONS: Young adults with SCD had significantly higher HU adherence compared to children and adolescents. Patients with lower HU adherence and/or chronic pain had increased health care utilization. Future studies examining barriers to adherence and evaluating interventions to optimize HU adherence in SCD are warranted. KEY MESSAGES: 1. Young adults with SCD had significantly higher HU adherence, as reflected in their laboratory markers, compared to children and adolescents. 2. Patients with higher HU adherence and/or those without chronic pain had lower or less frequent health care utilization. 3. No significant association of HU adherence to patients’ sex, socio-economic status and distance from hospital.