A Study to Learn About Sickle Cell Disease In Adult Patients

Inclusion Criteria (All Groups): \- Confirmed diagnosis of stable SCD (HbS/S or HbS/beta-zero-thalassemia). Additional Inclusion Criteria (No Disease Modifying Treatment Control Group): * Have experienced ≥1 episode(s) of medical utilization (MU) VOC within 12 months prior to Screening. * Data available for number of MU VOC(s) during the 12-month interval prior to Screening and a value for %fetal hemoglobin (HbF) collected subsequent to 1 year of age in the absence of recent transfusion. Additional Inclusion Criteria (SCD Disease Modifying Treatment Group): * Have experienced ≥1 episode(s) of MU VOC within 12 months prior to initiation of HU and/or crizanlizumab (whichever was initiated earlier). * Must be on a stable dose of their SCD treatment regimen ≥8 weeks prior to Day 1 with the intent of remaining on the same dose throughout the study, unless adjustments are medically necessary due to bone marrow suppression, in accordance with published guidelines and/or product specific guidance (eg, package label). Accepted SCD disease modifying treatment regimens include: * HU alone and/or in combination with crizanlizumab, L-glutamine and/or voxelotor; or * Crizanlizumab alone and/or in combination with HU, L-glutamine and/or voxelotor. * Data available for number of MU VOC(s) during the 12-month interval prior to initiation of any SCD disease modifying treatment, as described above, and a value for %HbF collected subsequent to 1 year of age, prior to initiation of any HU treatment, and in the absence of recent transfusion. Exclusion Criteria (All Groups): * Evidence or history of ongoing (condition or sequelae) clinically significant hematological (non-SCD), renal, endocrine, pulmonary, gastrointestinal, cardiovascular (including overt stroke but excluding silent cerebral infarct), hepatic (excluding cholelithiasis), psychiatric or neurological disease as assessed from medical records. * Marked ongoing bone marrow suppression as evidenced by any of the following as per medical record: severe anemia, absolute neutrophil count (ANC) \<1000 mm3 white blood cell (WBC), thrombocytopenia (platelet count \<100,000 mm3) within ≤8 weeks prior to Day 1 enrollment. * History of hematopoietic stem cell transplant or treatment with gene therapy as assessed from medical records. * History of simple transfusion within ≤4 weeks prior to Day 1 enrollment as assessed from medical records or participant self-report. * History of chronic transfusion/exchange transfusion within ≤12 weeks prior to Day 1 enrollment as assessed from medical records or participant self-report and/or plan to initiate such treatment during the 6-month observation period. Additional Exclusion Criteria (No Disease Modifying Treatment Control Group): * Participant received HU and/or crizanlizumab at any time within ≤18 months of Day 1 enrollment and treatment(s) was discontinued due to lack of efficacy (no reduction in the frequency of VOCs, documented or perceived) and/or plan to initiate said treatment(s) during the 6-month observation period. * Participant received voxelotor or L-glutamine within ≤4 weeks of Day 1 enrollment and/or plan to initiate said treatment(s) during the 6-month observation period.