| Summary: | **Background:** Hepatitis C virus (HCV) infection and its treatments are associated with significant symptoms, side effects and impact on patients functioning. The Hepatitis C Symptom and Impact Questionnaire version 4 (HCV-SIQv4) was developed according to FDA Patient Reported Outcomes (PRO) Guidance, for evaluating chronic HCV infection and its treatment.
**Objectives:** This study evaluated the psychometric properties and clinically important change (CIC) thresholds of the measure.
**Methods:** PRO data were pooled from three Phase IIb and III trials evaluating interferon-free simeprevircontaining regimens for treatment of chronic HCV infection. Scale range adequacy, reliability, validity, responsiveness and CIC thresholds were assessed incorporating knowledge of the appropriate measurement model.
**Results:** Data from 437 patients were analyzed. Stage of liver disease was associated with symptom severity and functioning at baseline. Reliability was acceptable (test-retest ICC ≥0.7) for most scores except the Gastrointestinal and Integumentary domains. Convergent validity was observed between HCV-SIQv4 scores and concurrent measures of conceptual similarity. Greater symptom severity and worse impact scores were associated with liver cirrhosis, depression, severe fatigue and health limitations. Patients who achieved SVR12 had better outcomes than those failing to. HCV-SIQv4 symptom and domain scores were responsive to changes in health state (effect sizes ≥0.5). Exploratory thresholds for change in scores indicating a clinically important improvement and worsening were HCV-SIQv4 Overall Body System Score (BSS), 8 and 8; Constitutional BSS, 10 and 10; Gastrointestinal BSS, 5 and 5; Psychiatric BSS, 8 and 8; Neurocognitive BSS, 8 and 8; and Integumentary BSS, 5 and 5.
**Conclusions:** The HCV-SIQv4 offers reliable, responsive assessments within HCV clinical development. CIC thresholds are now available to aid score interpretation.
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