A glomerular filtration rate calculator is a clinical tool used by health care providers to estimate kidney function in adults and children, according to the National Kidney Foundation. Glomerular filtration rates are calculated based on serum creatinine, age, gender and body size.
The National Kidney Foundation website has a chart that can be used to interpret GFR values. For example, a GFR value between 15 and 29 indicates severe loss of kidney function, and a GFR value of less than 15 indicates kidney failure. It is important for doctors to monitor their patients' kidney function periodically because the earlier kidney disease is detected, the better the prognosis for patients.