Reliability and validity of the NIDDK-QA instrument in the assessment of quality of life in ambulatory patients with cholestatic liver disease

The NIDDK-QA instrument, developed and widely used in liver transplant reci pients, assesses quality of life (QOL) in four domains, including liver dis ease symptoms, physical function, health satisfaction, and overall well-bei ng. We investigated whether the instrument may be used as a disease-specifi c instrument in ambulatory patients with cholestatic liver disease. The NID DK-QA instrument was administered in 96 patients with primary biliary cirrh osis (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 di scriminant and concurrent validity were examined. All patients were ambulat ory 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 (Cronb ach's alpha: 0.87-0.94) exceeded conventional acceptability criteria. The c orrelation between domain scores of the NIDDK-QA and SF-36 was clear and lo gical 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 m ental 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 ov erall 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. Thes e data, combined with our previous study, demonstrate its applicability in a wide spectrum of disease severity, ranging from early, ambulatory-phase d isease to decompensated cirrhosis necessitating liver transplantation.