The kidneys’ ability to filter is measured by determining the plasma creatinine level of plasma in a blood sample. The abbreviation used in Finland is P-Krea. Creatinine is normally created by the metabolism of muscles, and it leaves the body through the kidneys. If the kidneys’ ability to filter is diminished, less creatinine is removed and the blood creatinine level increases. Normally, the blood creatinine level is below 100 μmol/l for men and below 90 μmol/l for women.
The creatinine level increases when the functioning of the kidneys decreases. Nonetheless, the result depends on the person’s age, size and, especially, muscle mass. The creatinine level is higher in a muscular person compared to someone with less muscle mass, even if the operation of their kidneys are similar.
This is why the operation of the kidneys is monitored on the basis of the estimated glomerular filtration rate. The abbreviation is eGFR. Based on person's gender and age, the laboratory will calculate the estimated glomerulal filtration rate. The person's eGFR result is lower, if kidneys' functions are decreasing.