Development of a Disease-Specific Utility Instrument for Hemophilia.

Research has shown that disease-specific health-related quality of life (HRQoL) instruments are more responsive than generic instruments to particular disease conditions. However, only a few studies have used disease-specific instruments to measure HRQoL in hemophilia. The goal of this project was to develop a disease-specific utility instrument that measures patient preferences for various hemophilia health states. The visual analog scale (VAS), a ranking method, and the standard gamble (SG), a choice-based method incorporating risk, were used to measure patient preferences. Study participants (n=128) were recruited from the UT/Gulf States Hemophilia and Thrombophilia Center and stratified by age: 0 – 18 years and 19 +. Test retest reliability was demonstrated for both VAS and SG instruments, overall within-subject correlation coefficients were 0.91 and 0.79, respectively. Results showed statistically significant differences in responses between pediatric and adult participants when using the SG (p=.045). However, no significant differences were shown between these groups when using the VAS (p=.636). When responses to VAS and SG instruments were compared, statistically significant differences in both pediatric (p<.0001) and adult (p<.0001) groups were observed. Stratification of the study sample into mild, moderate and severe disease categories yielded no statistically significant differences in patient preference values among the three groups for both instruments (VAS (p =0.578 for mild vs. moderate, p =0.590 for mild vs. severe and p= 0.920 for moderate vs. severe and SG (p= 0.578 for mild vs. moderate, p = 0.590 for mild vs. severe and p=0.920 for moderate vs. severe). The utility measures obtained from this study can be applied in economic evaluations and decision models that analyze the cost/utility of alternative hemophilia treatments. Results derived from the SG indicate that age can influence patients’ preferences regarding their state of health. This may have implications for considering treatment options based on the mean age of the population under consideration. Data from this study also demonstrated that persons with varying severity of disease were able to objectively evaluate a wide range of health states for hemophilia. When assessing HRQoL for a rare disease such as hemophilia, it is important to establish that HRQoL measurements can be applied broadly across the population. Although the VAS and SG independently demonstrated reliability and validity, results indicate that the two measures may not be interchangeable.