[Measurement of renal function in clinical practice: principles and limitations].

Methods for measurement of glomerular filtration rate (GFR) (clearance in plasma, urine or both of an « exogenous » tracer, usually radio labeled) often are considered impractical from a clinical standpoint. Alternate methods proposed to estimate the GFR are based on plasma levels of « endogenous » tracers (creatinine, cystatin C). These methods are so imprecise that they provide little if any true reassurance with regards to warnings and recommended GFR values for the use of iodinated and gadolinium based contrast agents.