Glomerular filtration rate (GFR) is the best single measure of kidney function. A subnormal GFR is an important early indicator of possible chronic kidney disease. However, it also does not identify the cause. It is also not a ‘catch all’, for example, in early diabetes mellitus, GFR will typically be normal or even increased, due to ‘hyperfiltration’.Optimal detection and risk stratification of early kidney disease also requires measurement of urine albumin, rather than just eGFR.