What are the explanations for decreased accuracy of GFR estimates at higher levels of estimated GFR?
There are several possible explanations for reports of decreased accuracy of higher GFR estimates, including: (1) inter-laboratory variation in the calibration of serum creatinine assays, which has a larger effect at higher GFR levels (see question 13). This is likely an important reason for the wide variation among published studies; (2) greater biologic and measurement variability of GFR at higher values; and (3) limitations of generalizing an equation developed in one population to another population.9 These are the reasons that most clinical laboratories report GFR estimates as numerical values only when they are less than 60 mL/min/1.73 m2 (see question 29). The latter two explanations are also likely to affect estimating equations based on cystatin C.
