Letter to the Editor: “Diabetic Nephropathy: Has the Time Come to Move beyond Plasma Creatinine?”

Abstract

Diabetic nephropathy is the leading cause of kidney disease in patients with end stage renal disease and affects 40% of type 1 and type 2 diabetic patients. The major feature of diabetic nephropathy is an increase in urinary albumin excretion (UAE) in the absence of other renal diseases. Diabetic nephropathy is categorized into two stages: microalbuminuria (UAE >20 μg/ min and ≤199 μg/min) and macroalbuminuria (UAE 200 μg/min). In patients with type 2 diabetes or features of metabolic syndrome, screening for microalbuminuria should be performed at diagnosis and yearly thereafter. For type 1 diabetes, screening should be performed five years after diagnosis and then yearly. However, some diabetic patients were found to have normal UAE and a significant reduction in GFR. [1–3] The estimation of GFR is an indispensable tool to determine renal function in not only diabetic patients, but in the general population as well. In patients with type 2 diabetes in the NHANES III (Third National Health and Nutrition Examination Survey), low GFR (<60 mL · min –1 · 1.73 m –2 ) was present in 30% of patients in the absence of micro- or macroalbuminuria and retinopathy. [1] There are some patients with either type 1 or type 2 diabetes who have decreased glomerular filtration rate (GFR) in the presence of normal UAE. [2,3] In patients with type 1 diabetes, this phenomenon seems to be more common among female patients with longstanding diabetes, hypertension, and/or retinopathy. [2] These studies indicate that normoalbuminuria does not protect from a decrease in GFR in type 1 and type 2 diabetic patients. Therefore, GFR should be routinely estimated and UAE routinely measured for a proper screening of diabetic nephropathy. The recommended equation for GFR estimation by the National Kidney Foundation is the Modified Diet in Renal Disease (MDRD) equation: GFR (ml · min –1 · 1.73 m –2 ) = 186 × [serum creatinine (mg/dL) –1.154 × age (years) –0.203 × (0.742 if female) × (1.210 if African American)]. [4] The MDRD is readily accessible online at http://www. kidney.org/klsprofessionals/gfr_calculator.cfm. The reference range of GFR values in young individuals is from 80 to 130 ml · min –1 · 1.73 m –2 , declining at ~10 ml · min –1 · decade –1 after 50 years of age. [5]