Abstract: A method for calculating glomerular filtration rate (GFR) is revealed. A circumference of a patent's neck is measured and then is substituted into an exponential formula together with clinical factors and patient's age for estimating GFR. The present method has a better performance compared with methods for evaluating renal function by GFR available now. The methods available now have poor performance in prediction of loss of renal function at early stage. Some patients are diagnosed at an advanced stage so that they miss the opportunity of early treatment.