After 40 months , in patients receiving eicosapentaenoic acid-docosahexaenoic acid compared with placebo , the decline in creatinine-cystatin C-based GFR was 2.1 less ( 95 % confidence interval , 0.6 to 3.6 ; P < 0.01 ) ml/min per 1.73 m ( 2 ) ; other comparisons were not statistical significant .