RT Book, Section A1 Dirkx, Tonja C. A1 Woodell, Tyler B. A2 Papadakis, Maxine A. A2 McPhee, Stephen J. A2 Rabow, Michael W. A2 McQuaid, Kenneth R. SR Print(0) ID 1193127776 T1 The Kidney & Aging T2 Current Medical Diagnosis & Treatment 2023 YR 2023 FD 2023 PB McGraw-Hill Education PP New York, NY SN 9781264687343 LK accessmedicine.mhmedical.com/content.aspx?aid=1193127776 RD 2024/10/10 AB After 40 years of age, GFR declines annually by an average rate of 0.8 mL/min/1.73 m2 (though some older patients show little or no change) and is accompanied by a decline in renal mass that spares medulla relative to cortex. In an attempt to maintain GFR, renal blood flow decreases, causing a resultant increase in arteriolar resistance and increased filtration fraction. Serum creatinine values may remain relatively constant if muscle mass decreases in parallel with the decrease in GFR; a stable creatinine in the face of significant weight loss suggests progression of kidney disease.