Development and Validation of a Patient/Caregiver-Report Hydroxyurea Treatment Adherence Scale

Hydroxyurea (HU) is the only FDA-approved treatment for sickle cell disease (SCD). The National Heart, Lung and Blood Institute (NHLBI) recommends that any patient with HbSS and HbSβ⁰thalassemia ≥9 months old be offered HU treatment regardless of clinical severity to reduce SCD-related complications. However, HU is underprescribed due to provider and patient barriers, and patients are often nonadherent to prescribed HU treatment. Underutilization of and poor adherence to HU treatment are important gaps to address because life expectancy is improved in SCD patients taking HU. Therefore, this study aims to develop and validate a patient/caregiver-reported HU treatment adherence scale, Hydroxyurea Evaluation of Adherence for Life (HEAL) .

We surveyed 11 nationally renowned SCD experts to develop a question pool; hosted patient focus groups; refined the question pool based on focus group feedback; conducted a pilot study to evaluate the quality of items and psychometric properties of the draft questionnaire; and we will administer the final scale for analysis of validity, internal consistency reliability (ICR), and test-retest reliability. Validation measures will include global ratings (1-10 scale and Visual Analog Scale) from the subject and two of each subject's healthcare providers describing whether the patient takes HU as prescribed, a medication possession ratio, laboratory measures reflecting HU adherence (fetal hemoglobin [HbF], absolute neutrophil count [ANC] and absolute reticulocyte count [ARC]), and Medication Event Monitoring System (MEMS) bottle caps to calculate percentage of prescribed doses subjects receive. These measures will be correlated with HEAL scores to assess validity.

The provider survey resulted in a pool of 26 questions relating to adherence. Two patient focus groups were held in Jan 2016, one comprising 7 parents/caregivers of pediatric patients taking HU and the other, 8 adult patients taking HU. Participants evaluated the draft questionnaire to identify irrelevant questions, gaps, or challenges related to completion.

One hundred percent of focus group participants stated they would be willing to complete a HU adherence questionnaire if asked by their doctor to do so. All participants were comfortable with time required and ease of completion. 15% found some of the questions confusing. Participants identified a need to add questions about adherence when others (e.g., a former spouse) are responsible for administering HU to children and questions about the quality of the patient's relationship to the prescribing physician, which they identified as an important factor in their perception of and adherence to HU therapy. One hundred percent of participants expressed interest and willingness to use MEMS devices; there were no privacy concerns related to MEMS. Three parents (37.5%) were interested to see their child's data upon study completion; many felt that using MEMS might improve adherence.

After incorporating focus group participant feedback, HEAL contained 40 items divided into ten 4-item subscales (Dose, Remember, Plan, Cost, Benefit, Harm, Understand, Laboratory, Pharmacy and Provider Relationship). This version was administered to pilot samples from Jun to Dec 2016, comprising 15 parents/caregivers and 11 patients. ICR analysis found Cronbach's alpha=0.7 or higher for all scales except Harm and Provider Relationship. The Dose, Remember, and Plan subscales had the strongest psychometric properties.

Based on pilot study results, a final scale for validity testing has been created. The resulting scale is 24 items with 8 subscales (Dose, Remember, Plan, Cost, Understand, Benefit/Harm [one subscale], Laboratory, and Pharmacy). Due to inconsistencies on the Provider Relationship subscale, this subscale was removed and a VAS added to the Demographic Cover Sheet to rate the quality of the patient's relationship with the HU prescriber. This will allow HEAL results to be stratified by the quality of the Provider Relationship.

The HU adherence scale shows promise to be a reliable and valid measure of patient/caregiver adherence to a HU treatment regimen. Providing a total adherence score as well as subscale scores will allow identification of variables underlying nonadherence in patients who are prescribed HU therapy. The validation phase of this study is in progress; results are forthcoming.