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 Young adults with SCD had significantly higher HU adherence, as reflected in their laboratory markers, compared to children and adolescents. Patients with higher HU adherence and/or those without chronic pain had lower or less frequent health care utilization. No significant association of HU adherence to patients' sex, socio-economic status and distance from hospital.