Relationship between Vaso-Occlusive Crisis and Quality of Life: An Analysis of Patients with Sickle Cell Disease in the United States

Introduction: Sickle cell disease (SCD) affects approximately 100,000 people in the United States (US) today. SCD can lead to painful vaso-occlusive crises (VOCs), damage to major organs, increased vulnerability to severe infections, and as such, affects a patient's health-related quality of life (HRQoL). The objective of this study was to quantify how disease severity and the presence of VOCs affects patient quality of life, as measured by the economic metric of patient utilities. While previous studies (Anie et al. 2012) have measured utilities among patients with SCD in the United Kingdom (UK), this is the first US study to evaluate utilities in patients with SCD during and outside the experience of a VOC.

Methods: This study was a non-interventional, cross-sectional, online survey of patients with SCD. Individuals were recruited through SCD patient advocacy groups and a market research group. In this analysis, the outcome of interest was health utility values derived from the EuroQoL Five Dimension 5 level (EQ-5D) scale. Utility is a continuous measure of health status, where a utility of 1 represents perfect health, and a utility of 0 represents death. The EQ-5D survey responses were converted to EQ-5D health utilities using the United States EuroQoL value set, and EQ-5D health utility values (mean and 95% confidence intervals [CI]) were estimated. Respondents completed the EQ-5D question twice: once in reference to their health status when they were not experiencing a VOC and once in reference to their health status when experiencing a VOC. We estimated EQ-5D for both these measures. For EQ-5D not during VOC we estimated EQ-5D stratified by three classes of disease severity. These classes were informed by clinical expert severity. Respondents were classified as Severity Class I if they had no history of VOC requiring treatment by health care providers in the past year; Class II if they had ≥1 emergency department (ED) visit or hospital admission in the past year without organ damage; and Class III if they had long term organ damage (such as stroke or renal disease).

Results: 326 individuals were screened and 299 individuals were included in the final analytic sample. Among these individuals, the average age was 34.3 years (range 18 - 72); 219 (73.2%) were female and 1 (0.3%) was non-binary. Based on self-report of VOC, as well as presence of complications and organ damage of individuals, 79.6% (238/299) were Severity Class III, 12.0% (36/299) were Class II, and 8.4% (25/299) Class I. The estimated health utility value derived from EQ-5D during VOC was 0.311 (95% CI: 0.286, 0.337). The estimated health utility values not during a VOC derived from EQ-5D was 0.733 (0.713, 0.753) for Severity Class III and 0.775 (0.725, 0.826) for Severity Class II. This result suggests >5% worse health status utility in Class III than Class II disease severity, although a Wald t-test for difference in means did not suggest evidence of a statistically significant difference in utility (p-value 0.13).

Conclusion: The presence of VOC had a more severe impact on HRQoL for patients with SCD than previously estimated. When not experiencing a crisis, patients with Severity Class III, indicated by presence of organ damage, had >5% worse HRQoL than those with Severity Class II.