Methods

In this retrospective cohort study, patients aged between 8 and 18 years with a confirmed diagnosis of SCD, who received care at the Emma Children’s Hospital, Amsterdam University Medical Centers (Amsterdam UMC) were eligible for enrollment. As part of standard care procedures, children routinely filled out PROMs prior to the regular visits through the online KLIK PROM portal (https://www.hetklikt.nu/). The answers were returned to the clinician and discussed during consultation. One of the measures is the Pediatric Quality of Life Inventory 4.0 Generic core scales (PedsQLTM 4.0). Every child (and/or the parent) was requested to complete the PedsQL at least once a year. Patients were included in this study if they had filled out at least two PedsQLs between January 2012 and September 2021. Data of patients were excluded if patients were on a chronic transfusion therapy or if permission for use of data for research purposes had been denied. This project was reviewed by the Medical Research Ethics Committee of the Amsterdam UMC, and conducted according to the Declaration of Helsinki.

Study measures

Demographics and disease-related characteristics including age, gender, SCD genotype, medication use, and hospitalization for VOC were collected from the electronic health records (EHR). Details of hospitalization for VOC one year prior to HRQOL measurement were collected from the EHR as well including length of stay (LOS), analgesic use and complications during hospital admission such as development of acute chest syndrome. With this information, the severity of each hospital admission was scored as mild (1 point), moderate (2 points) or severe (3 points). Mild severity was defined as a LOS shorter than 4 days; moderate severity was defined as a LOS between 4 through 6 days; and severe was classified as the presence of an acute chest syndrome independent of LOS, or a LOS more or equal to 7 days.
Self-reported HRQoL was collected by completion of the PedsQL through the online KLIK PROM portal. The PedsQL consists of 23 items covering the following 4 subscales: physical, emotional, social and school functioning.30,35 The questions address the preceding week and could be answered with the following options: never (0), almost never (1), sometimes (2), often (3) and almost always (4). The answer ‘0’ is converted into the score of 100, ‘1’ into 75, ‘2’ into 50, ‘3’ into 25 and ‘4’ into 0. Then, a mean score was computed for each of the 23 items, and transformed to a scale that ranges from 0 to 100. Both a total score as well as a score for each HRQoL subscale was calculated. A psychosocial score was created from the emotional, social and school functioning subscales of the PedsQL. A weighted average of the different PedsQL subscale scores was calculated to derive the total HRQoL score. The higher the calculated scores, the higher the perceived HRQoL.36 Previous studies confirmed the validity and reliability of the PedsQLTM for the measurement of HRQOL in the Dutch population.30 To evaluate the reliability of the PedsQL versions in our study population, we calculated internal consistency estimates (Cronbach’s α). Estimates of 0.70 or greater were considered good, while estimates between 0.60 and 0.70 were considered moderate and estimates below 0.60 were considered poor.37

Statistical analyses

All data was transformed and analyzed in the Statistical Package for the Social Sciences (SPSS) version 28.0. Descriptive data were generated for all variables to describe the study population and its characteristics. Categorical variables were presented as absolute numbers with corresponding percentages. Means and standard deviations (SDs) were calculated for continuous variables that were normally distributed. Medians with interquartile ranges (IQRs) were calculated for values that were not normally distributed. The period of follow-up was expressed in patient-years by summarizing the duration of follow-up in days for all patients divided by the number of days in a year (365.25). Baseline characteristics and mean HRQoL scores were compared between the hospitalization and no hospitalization for VOC group using the chi-squared test or the unpaired t-test. For analysis purposes, genotype was categorized in two groups: a clinically mild (HbSC and HbSß+-thalassemia) and clinically severe genotype (HbSS and HbSß0-thalassemia).
To assess the impact of the occurrence of hospitalization for VOC on HRQoL over time, linear mixed model (LMM) analysis was used. The dependent variables were HRQoL scores (both the total and the subscale scores), and the independent variable was hospitalization for a VOC. In all analyses, patients were considered as non-hospitalized if they had not been admitted to the hospital in the last 12 months. Sensitivity analyses were performed to determine whether the time period between hospital admission and HRQoL measurement, affected HRQoL. For this, the analyses were repeated for the time periods 3, 6, 9 and 12 months after hospitalization. The impact of frequency of hospital admission in 12 months on HRQoL was evaluated using LMM analyses as well. To assess the impact of the severity of a hospitalization for VOC on HRQoL over time, a subanalysis with LMM was performed within the hospitalization group using the calculated severity score. All analyses were adjusted for age and SCD genotype. The estimates of the LMM analyses were reported as regression coefficient (β). Significance levels were set at 5% and all estimates were reported with 95% confidence interval (CI).