Assessing Physical Function in Sickle Cell Patients Taking Voxelotor

Inclusion criteria

• Provision of signed and dated informed consent form
• Stated willingness to comply with all study procedures and availability for the duration of the study
• Male or female,
• aged 18-65 years
• Diagnosis of sickle cell disease with HbSS, HbSc, HbS-beta thalassemia genotypes
• Hemoglobin level of 6 g/dL - 10.5 g/dL
• Between 0 and 10 vaso-occlusive (VOC) episodes in previous 12 months
• Ability to take oral medication and be willing to adhere to the voxelotor regimen
• For females of reproductive potential, they will be educated to avoid pregnancy during study period and for one month after due to limited data surrounding pregnancy and voxelotor
• For males of reproductive potential: use of condoms or other methods to ensure effective contraception with partner
• Agreement to adhere to Lifestyle Considerations (see section 5.3) throughout study duration

Exclusion criteria

• Hemoglobin results < 6 g/dL or > 10.5 g/dL
• Patients receiving hydroxyurea who have had a dose change within the prior 3 months
• Females who are breastfeeding or pregnant
• Patients who are receiving regularly scheduled blood (RBC) transfusion therapy (also termed chronic, prophylactic, or preventive transfusion) within 30 days of 6MWT
• Any form of hepatic dysfunction as demonstrated by alanine aminotransferase (ALT) >4 × ULN or Child-Pugh Class C
• Acute kidney injury or chronic renal disease with estimated glomerular filtration rate<30mL/min/1.73 m2
• Current or previous diagnosis of malignancy within the last two years excluding local therapy for non-melanoma skin malignancy
• Unstable cardiopulmonary disease within the last 6 months prior to study enrollment
• Any conditions including behavioral or medical that in the opinion of the investigator, may negatively impact informed consent, participation and study interpretation
• Current use of commercially available voxelotor
• Prior hypersensitivity to voxelotor or its excipients
• Patients with baseline gait and other physical impairments that would limit 6MWT and other functional assessment at discretion of the investigator
• Patients who on day of assessment present with vaso-occlusive crisis or rate their pain greater than 6 on a scale of 1-10 using the Numeric Rating Scale will not be assessed that day and re-screened at the investigator's discretion.