While reading this article your kidneys filter about half a liter of blood (120 mL/minute). Kidneys are such efficient organs that people can sustain a normal and healthy life with only one kidney. Therefore, it is even possible for healthy individuals to donate one of their kidneys to people with severe kidney disease or kidney failure.
In kidney disease, patients suffer from constant loss of kidney function. As the filter capacities of one healthy kidney is sufficient, patients are rarely affected by early signs or symptoms of chronic kidney disease (CKD). To slow or even stop the progression of CKD, and maintain the remaining kidney function, early diagnosis and constant monitoring of kidney function is important.
The most common method to access kidney function is the measurement of creatinine in blood and urine. Serum creatinine levels begin to rise above the normal ranges when kidney function is already decreased by 50% and creatinine levels are dependent on age, sex, diet and other factors. Creatinine is also used to estimate the glomerular filtration rate (GFR), but has weaknesses in the “creatinine blind-range” defined by a GFR of 40 to 80 mL/min/1.73m², early stages of CKD and some patient groups. The use of additional parameters is recommended and implemented by the KDIGO.