Accuracy of creatinine-based and cystatin C-based eGFR formulas compared to plasma iohexol clearance in children after cardio-pulmonary bypass

ACCURACY OF CREATININE-BASED AND CYSTATIN C-BASED eGFR FORMULAS COMPARED TO PLASMA IOHEXOL CLEARANCE IN CHILDREN AFTER CARDIO-PULMONARY BYPASS E. Dhont, C. Windels, A. De Jaeger, S. Croubels, J. Vande Walle, P. De Paepe, P.A.J.G. De Cock Background and aims Identification of patients with altered renal function after cardio-pulmonary bypass is often delayed due to lack of accurate methods for evaluation of glomerular filtration rate. We aimed to evaluate performance of eGFR formulas based on serum creatinine (Scr) and cystatin C (CysC) in comparison with iohexol clearance (CLiohex) after cardiac surgery. Methods Children who underwent cardiopulmonary bypass were included. After iohexol bolus injection, CLiohex was calculated from the plasma disappearance curve over a 360-minutes interval. Volumetric Absorptive Microsampling was used for iohexolsampling. CLiohex was compared with eGFR by 10 Scr- based and 11 CysC-based formulas. Accuracy of eGFR formulas was described as the percentage of GFR estimates within ±30% of CLiohex. AKI was defined as a decrease of GFR measured by CLiohex of ≥ 25 % of age-specific GFR reference values. Results 19 patients, median age 2 months (range:0,13-135), were included after closure of ASD (n=1), VSD (n=3), AVSD (n=3), arterial switch procedure (n= 8), ROSS procedure (n=1), Norwood procedure (n=1), coronary surgery (n= 1) and truncus arteriosus repair (n= 1). Median CLiohex was 62 ml/min/1.73m2 (range 29-231). 21% of patients showed some degree of AKI according to CLiohex. eGFR formulas had a relatively good correlation with CLiohex, however, accuracy was poor; none of the eGFR formulas showed P30>75%. Widely used Schwartz formula performed unsatisfactory with P30=53%. Conclusions eGFR formulas based on Scr or CysC seem inaccurate to assess GFR in children after cardiac surgery. CLiohex could offer a feasible and safe alternative to reliably evaluate renal function in these vulnerable patients