LAUSR

Background Kidney involvement is common in systemic sclerosis (SSc) and proteinuria or renal crisis are associated risk factors for increased mortality in SSc. For the measurement of the kidney function (glomerular filtration rate, GFR) the creatinine-based estimation formula of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and the Modification of Diet in Renal Diseases (MDRD)-formula are commonly used. Cystatine C has a higher diagnostic sensitivity to show a reduction of GFR. As it is not being influenced by muscle mass or diet it has an advantages over the creatinine-based measurements. Objectives Comparison of the creatinine-based and cystatin C-based eGFR in systemic sclerosis patients. Methods Single-centre, retrospective analysis of SSc patients between 2015–2017 which were parallel tested for serum creatinine and cystatine C. 108 patients (78 females, 30 males), 21 patients with diffuse systemic sclerosis (dcSSc), 76 patients with limited systemic sclerosis (lcSSc) and 11 patients with overlap syndrome. Medium age 58,8 (±16,1 years), age span 17–83 years. For the calculation of the estimated glomerular filtration rate (eGFR) the following formulas were used: MDRD-Study Equation, CKD-EPI Creatinine Equation 2009. CKD-EPI Cystatin C Equation 2012 Results The mean eGFR according to the CKD-EPI Creatinine Equation was 84,4 ml/min (±23,5), according to the MDRD formula it was 80,24 ml/min (±22,8) (p<0,001) and 65,3 ml/min (±21,7) (p<0,001) when the CKD-EPI Cystatin C Equation was used. According to the KDIGO stages of chronic renal impairment a stage G2 (eGFR <90 ml/min) was present in 39,8% of the patients (43/108) using the CKD-EPI Creatinine Equation, in 47,2% (51/108) using MDRD and in 48,1% (52/108) using the CKD-EPI Cystatin C Equation. A relevant chronic kidney impairment stage G3 (eGFR <60 ml/min) or higher was present in 14,8% of the patients (16/108) calculated by CKD-EPI Creatinine Equation, in 17,6% (19/108) of the patients according to MDRD Equation and in 38,8% (42/108) according to CKD-EPI Cystatin C Equation. Patients with a higher difference (>18 ml/min) between creatinine-based and cystatin C-based eGFR did not differ in age, body mass index (BMI) or disease subset from patients with a lower difference but a higher difference occurred significantly more often in men (p=0,012). Conclusions Many patients with SSc showed a significant difference using cystatin C for the calculation of GFR compared to the creatinine-based formulas. As reduced muscle mass is common in SSc this could be due to sarcopenia in the context of the underlying disease. Early detection of impaired kidney function might be useful to monitor disease progress and is important for the management of immunosuppressive drugs like methotrexate and cyclophosphamide which are commonly used in the disease but need to be adjusted to the renal function. A prospective study with measurement of GFR and comparison of different formulas in this patient population seems necessary. Disclosure of Interest None declared