What is GFR

Marker to determine the GFR

Creatine

The creatinine level is determined in the patient's blood (serum) and is one of the most important laboratory determinations. Creatinine is a breakdown product of creatine and serves as an energy store in muscles. The creatinine level in the blood is therefore also dependent on the patient's muscle mass. Creatinine has established itself as a marker, but is not ideal because of the creatinine-blind area. Creatinine blind means that kidney function is already declining without creatinine changing.

Women and men have different energy reserves in the muscle. Creatinine is almost completely pressed (filtered) into the urine via the kidney corpuscles (glomeruli). With impaired kidney function, the glomeruli can no longer adequately filter the creatinine, with the result that it accumulates in the blood.

In a study on 1,628 patients with chronic kidney disease, the serum creatinine determination overestimated the actual kidney function by more than 30% on average (Ann Intern Med 1999). The relationship between serum creatinine and GFR is not linear. There is a “creatinine-blind area”. Individual patients can have severely impaired kidney function <30 ml / min even with serum creatinine values ​​of <1.5 mg / dl.

For determining the eGFR using creatinine in adults

Cystatin C.

Cystatin C is a small protein (a so-called protease inhibitor) that is completely glomerularly filtered, tubularly reabsorbed and catabolized. Cystatin C is produced in almost all cells. In contrast to creatinine, cystatin C increases with a slight reduction in the GFR and is therefore used as an ideal marker for estimating the GFR. The formation rate is stable and independent of inflammatory processes (e.g. acute phase reaction), liver disease, muscle mass, eating habits and age.

With cystatin C, a decrease in GFR can be identified better with normal kidney function than with serum creatinine or GFR formulas.

Cystatin C has benefits

  • in the early detection of reduced kidney function
  • in diabetes mellitus
  • in the elderly and children with underweight and overweight
  • for calculating the dose of toxic drugs
  • for monitoring kidney function in the post-transplant phase
  • especially with disturbance of the creatinine measurement

For determining the eGFR using cystatin C in adults

Additional information

More information for nephrologists is available at: Frequently Asked Questions about GFR Estimates. New York: The National Kidney Foundation (NKF) 2011.