Reliability and Validity of the Niddk–Qa Instrument in the Assessment of Quality of Life in Ambulatory Patients With Cholestatic Liver Disease

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Abstract
The NIDDK–QA instrument, developed and widely used in liver transplant recipients, assesses quality of life (QOL) in four domains, including liver disease symptoms, physical function, health satisfaction, and overall well–being. We investigated whether the instrument may be used as a disease–specific instrument in ambulatory patients with cholestatic liver disease. The NIDDK–QA instrument was administered in 96 patients with primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) seen at the Mayo Clinic. The SF–36, a well–established generic instrument, was also administered. Standard measures for test–retest reliability, internal consistency, and discriminant and concurrent validity were examined. All patients were ambulatory with mostly normal levels of serum bilirubin and albumin concentrations. The reliability of the NIDDK–QA, as measured by test–retest correlation (Pearson coefficients: 0.82–0.99, P < .01) and by internal consistency (Cronbach's alpha: 0.87–0.94) exceeded conventional acceptability criteria. The correlation between domain scores of the NIDDK–QA and SF–36 was clear and logical in that the physical function domain of NIDDK–QA strongly correlated with the physical component summary score of SF–36 (r = 0.86, P < .01). The overall well–being domain of the NIDDK–QA was closely associated with the mental summary score of SF–36 (r = 0.69, P < .01). Among PBC patients, there was a modest yet significant correlation between the Mayo risk score and overall well–being (r = -0.26, P = .03). In the assessment of QOL in patients with cholestatic liver disease, NIDDK–QA is found reliable and valid. These data, combined with our previous study, demonstrate its applicability in a wide spectrum of disease severity, ranging from early, ambulatory–phase disease to decompensated cirrhosis necessitating liver transplantation.