[How I examine...diabetic nephropathy. Second part: assessment of glomerular filtration]

The natural history of diabetic renal disease can be divided into different stages according to the degree of albuminuria and the level of glomerular filtration rate (GFR). Assessment of the early hyperfiltration state, as well as determination of the rate of decline in kidney function at a later stage require precise and accurate methods to measure GFR. In this article, we briefly remind the reader of the physiological basis of GFR. We then review the different techniques for the monitoring of kidney function (inulin clearance, endogenous creatinine clearance, plasma disappearance of a radiolabelled tracer) and discuss the pro and cons of each of them in different clinical settings. Finally, we try to define a rational use of these techniques in everyday clinical practice.