Cystatin C is not a better estimator of GFR than plasma creatinine in the general population

Area of Science:

• Nephrology
• Clinical Chemistry
• Epidemiology

Background:

• Accurate glomerular filtration rate (GFR) measurement is crucial but complex.
• GFR is often estimated using creatinine or cystatin C levels.
• Cystatin C-based estimates are hypothesized to be superior for near-normal GFR and cardiovascular disease prediction.

Purpose of the Study:

• To compare the accuracy of cystatin C and creatinine-based GFR equations in a general middle-aged population.
• To determine if cystatin C estimates offer advantages over creatinine estimates for GFR near normal ranges.
• To investigate the implications for cardiovascular disease prediction.

Main Methods:

• Measured GFR using iohexol clearance in 1621 middle-aged individuals without specific comorbidities.
• Evaluated bias, precision, and accuracy of published cystatin C and creatinine GFR equations.
• Compared performance metrics including percentage of estimates within 30% of measured GFR (mGFR).

Main Results:

• The most accurate cystatin C equation achieved 94% accuracy, with a bias of 3.5 and precision of 18 ml/min/1.73 m².
• The most accurate creatinine equation achieved 95% accuracy, with a bias of 2.9 and precision of 15 ml/min/1.73 m².
• A combined cystatin C and creatinine equation showed 92% accuracy, bias of 7.6, and precision of 15 ml/min/1.73 m².

Conclusions:

• GFR estimates based on cystatin C were not superior to creatinine-based estimates in this general population sample.
• The superior cardiovascular disease prediction by cystatin C observed in other studies may be attributed to factors beyond GFR estimation.
• Creatinine-based equations demonstrated comparable or superior accuracy and precision for GFR estimation in this cohort.