Background/Aims: Diabetic foot ulcers (DFU) negatively affect the quality of life (QoL) of people with diabetes. The DFU Scale Short Form (DFS-SF) is a validated disease-specific patient-reported outcome measure (PROM) for measuring health-related quality of life among DFU patients. It consists of 29 items in 6 subscales: leisure, physical health, dependence/daily life, negative emotions, worried about ulcers and bothered by ulcer care. This study aimed to validate the DFS-SF questionnaire for Flemish Dutch-speaking patients with DFU in Belgium.
Methods: This observational cohort study included 100 patients with DFU from the multidisciplinary diabetic foot clinic of Onze-Lieve-Vrouw Hospital Aalst, Belgium. DFS-SF items were reverse-coded so that high DFS-SF scores indicate better quality of life. Reliability was assessed through the test-retest reliability (intraclass correlation coefficient (ICC)), internal consistency (Cronbach’s alpha) and measurement error (agreement). Spearman's correlations and known-group comparisons were conducted to examine construct validity. Correlation with EQ-5D-5L was used to test criterion validity. The full study protocol has been published earlier (Rezaie et al. 2019. doi:10.1136/bmjopen-2019-034491).
Results: The majority of the patients were men (71.1%), with a mean age of 67.7±10.3 years and mean diabetes duration of 20.1±12.5 years. 81 patients (83.5%) had type 2 diabetes. Ischemia was present in 31.7% of the patients, neuropathy in 88.5%. Most DFU were deep (93.2%) and showed signs of infection (60,6%). ICC of the different DFS-SF subscales ranged from 0.36 to 0.84. Cronbach’s alpha was between 0.70 and 0.92 for all subscales. Agreement varied between 2.83 and 14.52. A ceiling effect was observed in the subscales leisure, dependence/daily life, negative emotions and bothered by ulcer care. None of the 6 predefined hypotheses to determine the construct validity was confirmed. The different DFS-SF subscales showed a moderate to strong correlation with the EQ-5D-5L index value. The DFS-SF subscales were not sensitive to ulcer changes over time.
Conclusions: The psychometric properties of the Flemish-Dutch version of the DFS-SF questionnaire were not confirmed nor showed a good sensitivity to ulcer changes in our patient population. The disease-specific DFS-SF provided no relevant additional information on quality of life beyond the general EQ-5D-5L.
