Background: Although non-alcoholic fatty liver disease (NAFLD) is considered to be associated with chronic kidney disease (CKD), long-term follow up data is lacking. We investigated whether NAFLD, as determined by the fatty liver index (FLI), could predict incident CKD in 10-year prospective cohort study. We also assessed the clinical utility of FLI to predict the development of CKD.

Methods: 6,238 adults aged 40 to 69 years without baseline CKD from the Ansan - Ansung cohort were examined. Patients were classified according to FLI as follows: FLI<30, no NAFLD; FLI≥60, NAFLD; and 30≤ FLI<60, intermediate. Incident CKD was defined as estimated glomerular filtration rate (eGFR) <60 ml/min per 1.73 m2. The clinical utility of FLI in predicting incident CKD was estimated via area under the receiver-operating characteristic curve (AUC), net reclassification improvement (NRI), and integrated discrimination improvement (IDI) analyses. 

Results: During an average of 10 years of follow-up, 724 subjects (15.21 %) developed CKD. The adjusted odds ratio [95% confidence interval (CI)] for incident CKD increased in a graded manner with FLI increased (<30 vs. 30-59 vs. ≥60= 1 vs. 1.16 [0.93-1.43] vs. 1.43 [1.07-1.89], respectively, P for trend=0.0439). Incorporation of FLI into traditional risk factors of CKD significantly increased prediction of incident CKD based on NRI (17%; 95% CI, 8.9-25%; P-value <0.001) and IDI (0.002; 95% CI, 0.0046-0.0143; P-value=0.046).
  
Conclusions: FLI, a surrogate marker of NAFLD, was an independent risk factor for incident CKD. FLI provides meaningful incremental risk reclassification beyond that of conventional risk factors of CKD.

The fatty liver index as a predictor of incident chronic kidney disease in a 10-year prospective cohort study