Use of desirability functions to evaluate health status in patients with cirrhosis

Abstract

There is a need for methods that provide a quantitative assessment of a patient's global health status, especially as regards quality of life, prognosis, and impact of therapeutic interventions. We propose that desirability functions, widely used in industrial quality control, can be adapted to obtain a numerical "wellness" score, incorporating numerous easily measured clinical parameters, that reflects a patient's overall clinical status and prognosis on a scale from 0 (worst) to 1 (best). In this pilot study, we used this approach to develop a Cirrhosis Relative Wellness Index for use with patients with liver disease. We relied on expert opinion to select 10 parameters of interest and to determine the desirability function for each parameter. A composite index was then developed and tested using data from 109 cirrhotic subjects enrolled in the North American Study for the Treatment of Refractory Ascites (NASTRA). The index was independently validated using a separate database obtained from a review of records of 1342 cirrhotic patients referred for liver transplantation candidacy in the Veterans Health System between 1997 and 2008. In both datasets, the Cirrhosis Relative Wellness Index was significantly associated with transplant-free survival using either a proportional hazards model or a logrank test (where the index was dichotomised). Desirability function modelling represents a promising new approach to quantitatively estimating global health status.