#2904 Chronic kidney disease staging in the very old: the role of cystatin C
Authors: López Begoña Padrones , Menéndez Lucía Ovies , Roldán Libia Cristina Pérez , Martínez Jusmer Kennyon Serrano , Herrera Laura Manuela Robayo , Muñoz Javier Montero , Fernández Alejandra Fernández , Rodríguez Iván Veloso , Gil-Albert Carmen García , García Minerva Rodríguez , Alonso Carlos Gómez , López Álvarez Eva María 
Published: May 2024

Abstract

Background and Aims
Over the past decade, an unanswered question has emerged: which is the best equation for estimating glomerular filtration rate (eGFR) in older patients with chronic kidney disease (CKD)? Despite the lack of consensus, cystatin C appears to hold promise, as it is not influenced by factors often affected in the very elderly, such as muscle mass or protein intake, offsetting the limitations of creatinine-dependent formulas. This may have implications for correctly classifying patients across the different stages of CKD.
The aim of this study is to analyze the concordance between different eGFR formulas and the Chronic Kidney Disease Epidemiology Collaboration formula combining the use of creatinine and cystatin C (CKD-EPIcr-cys), which is recommended by the European Renal Best Practice Group.

Method
A cross-sectional observational study was conducted with patients ≥85 years old with CKD admitted to an Acute Geriatric Unit due to acute illness over a period of four months. Variables included age, sex, previous Barthel Index (BI), dementia (defined by Reisberg's GDS≥4), frailty (FRAIL scale ≥3), polypharmacy (≥5 drugs), comorbidities (degree of CKD according to CKD-EPI, hypertension, diabetes mellitus, dyslipidemia, chronic heart failure (CHF), Charlson Comorbidity Index (CCI)), nutritional and laboratory parameters (Mini Nutritional Assessment-Short Form (MNA-SF), body mass index (BMI), serum cholesterol and albumin, glucose, glycated hemoglobin), and estimated glomerular filtration rate at admission by CKD-EPIcr-cys, CKD-EPIcys, CKD-EPI, MDRD and Cockcroft-Gault. The intra-class correlation coefficient (ICC) and the Kappa index were used to analyze concordance.

Results
A total of 407 patients were recruited, with a mean age of 90.7±4.1 years, 68.1% female. The previous BI was 59.1±32.3. Dementia was present in 28.3%. Frailty was noted in 66.6%, and polypharmacy in 90.9%. CKD stage: G3a (37.6%), G3b (44.2%), G4 (17.7%), G5 (0.5%). Comorbidities included hypertension (90.7%), CHF (68.3%), dyslipidemia (53.8%), and diabetes mellitus (37.8). The CCI was 2.9±1.8. MNA-SF score was 9.5±2.4 (18.4% malnutrition), and average BMI was 28±5.5 kg/m2 (29% obesity). The mean values for cholesterol, albumin, glucose, and glycated hemoglobin were 156.3±47.7 mg/dL, 35.5±4.6 g/L, 126.1±91.3 mg/dL, and 5.9±2%, respectively. The eGFR at admission according to CKD-EPIcr-cys was 31.9±12.2 mL/min/1.73 m2, while using CKD-EPI, CKD-EPIcys, MDRD, and Cockcroft-Gault were 37.5±14.5 mL/min/1.73 m2, 28.2±12.1 mL/min/1.73 m2, 42.8±16 mL/min/1.73 m2, and 30.4±11.7 mL/min/1.73 m2, respectively.
The formulas showed high concordance with CKD-EPIcr-cys: CKD-EPI (ICC=0.90 [0.52 to 0.96; p &lt; 0.001]), CKD-EPIcys (ICC=0.94 [0.79 to 0.97; p &lt; 0.001]), MDRD (ICC=0.80 [-0.14 to 0.94; p &lt; 0.001]), Cockcroft-Gault (ICC=0.86 [0.82 to 0.88; p &lt; 0.001]). However, when comparing stratification into different stages of CKD, the concordance with the various formulas was lower: CKD-EPI (k=0.4; p &lt; 0.001), CKD-EPIcys (k=0.59; p &lt; 0.001), MDRD (k=0.12; p &lt; 0.001), Cockcroft-Gault (k=0.4; p &lt; 0.001). When referencing CKD-EPIcr-cys, it is notable that only 34.3% of patients were correctly classified using MDRD, followed by CKD-EPI (57.1%), Cockcroft-Gault (59.8%), and CKD-EPIcys (73%). Specifically, of the patients classified as stage G4 according to CKD-EPIcr-cys, there was a reclassification to stage G3b in 2.1% (CKD-EPIcys), 18.1% (Cockcroft-Gault), 33.3% (CKD-EPI), and 52.1% (MDRD).

Conclusion