Chronic kidney disease - Epidemiology collaboration equations even using cystatin C overestimate renal function in patients with chronic intestinal failure on long-term parenteral nutrition.

Background & Aims: Accurate determination of renal function is of utmost importance in chronic intestinal failure (CIF) patients on parenteral nutrition (PN) and creatinine based glomerular filtration rate (GFR) estimating equation is used in clinical practice. The aim of the present study is to evaluate the reliability of 3 CKD-EPI GFR estimating equations (eGFR) (creatinine, cystatin C or combined creatinine/cystatin C) compared with the reference method which is Iohexol plasma clearance (mGFR) in patients on long-term PN (>6 months) owing to CIF.

Methods: Forty-eight patients (25 F) with a median age of 58 years (Interquartile Range:15) presenting CIF on PN for a median duration of 93 months (75) were included in this retrospective study. Concordance studies were performed by Pearson correlation and Bland-Altman method (Mean bias-Confidence Interval). Accuracy of the formulas was estimated with P30 representing the proportion of eGFR within 30 % of mGFR (±30 %).

Results: Median mGFR was 65 (29) ml/min/1.73 m and the median eGFR was 85 (43) ml/min/1.73 m with 2009 CKD-EPIcreatinine, 74 (47) ml/min/1.73 m with 2012 CKD-EPIcystatin and 75 (48) ml/min/1.73 m with 2012 CKD-EPIcombined Cystatin C/Creatinine based formulas. The agreements were not acceptable for clinical practice. Median bias as well as lower and upper confidence intervals were for mGFR vs. eGFR (2009 CKD-EPIcreat): +21,1 (16.7,25.3), for mGFR vs. eGFR (2012 CKD-EPIcyst): +14.4 (12.9,20.5) and for mGFR vs. eGFR (2012 CKD-EPIcomb): +9.3 (7.9,15.5). Accuracy of all formulas estimated by P30 was less than 80 %. With the 3 eGFR equations, more than 46 % of patients were poorly stratified according to the classification of chronic kidney disease (CKD) with an overall tendency towards underestimation of the disease severity. Forty-seven percent of the patients had mGFR<60 ml/min/1.73 m corresponding to CKD Stage III or worse.

Conclusions: The eGFR estimating CKD-EPI equations significantly miscalculate the true levels of renal function in patients with CIF on PN and should be used with caution in daily clinical practice.