Psychometric evaluation of the hepatitis C virus patient-reported outcomes (HCV-PRO) instrument: validity, responsiveness, and identification of the minimally important difference in a phase 2 clinical trial.

PURPOSE

To describe the psychometric properties and identify the minimally important difference (MID) of the hepatitis C virus patient-reported outcomes (HCV-PRO) instrument. Chronic HCV infection and associated treatments negatively affect PROs of function and well-being.

METHODS

In a phase 2 trial, HCV-infected patients received direct-acting antivirals (DAAs) for 12 weeks with peg-interferon/ribavirin (peg-IFN/RBV) for 48 weeks, or placebo plus peg-IFN/RBV. The HCV-PRO total score, SF-36 PCS and MCS scores, EQ-5D-3L, and EQ VAS were measured at baseline, week 8, end of DAA treatment (EODT), end of peg-IFN/RBV treatment (EOT), and posttreatment week 24 (SVR24). Convergent validity of the HCV-PRO was assessed by Pearson's correlation coefficients. Discriminant validity was assessed by analyzing mean HCV-PRO total scores by EQ-5D anxiety/depression and pain/discomfort domain scores (none vs. some) and presence/absence of depression or fatigue adverse events. MID was identified through effect size (ES) and receiver-operating characteristic (ROC) curve analyses (HCV-PRO response vs. SF-36 PCS/MCS and EQ VAS MID thresholds).

RESULTS

In 74 patients (22 % female; 81 % White; 51 % ≥50 years), correlations (0.64-0.96) between HCV-PRO total scores, SF-36 PCS/MCS scores, and EQ VAS scores at all time points supported convergent validity. HCV-PRO total scores were reduced to 10-30 points in patients impaired by depression, pain, or fatigue symptoms. Impact of peg-IFN/RBV regimen on HCV-PRO ES increased over time (EODT -0.76; EOT -0.93). ES and ROC curve analyses indicated an MID of -10 points.

CONCLUSION

The HCV-PRO was valid and responsive in the population studied. An MID of -10 points represented a threshold of clinical significance for the HCV-PRO.