13.20: Drug Dosing in Renal Diseases: Estimation of Glomerular Filtration Rate Based on Serum Creatinine Concentration

Glomerular filtration rate (GFR) can be estimated from serum creatinine using the modification of diet in renal disease (MDRD) formula or the chronic kidney disease–epidemiology collaboration (CKD–EPI) equation. Both methods are widely used in clinical practice to assess kidney function and guide treatment decisions.

The MDRD equation does not require weight or height measurements and is normalized to the body surface area of 1.73 m², considered the average adult surface area. This equation is particularly advantageous for estimating GFR in older and obese individuals, providing more accurate results than in healthy subjects. By eliminating the need for weight and height, the MDRD equation simplifies estimating kidney function.

The CKD–EPI equation was developed to provide a more precise estimate of GFR, especially when GFR levels are higher. It is based on serum creatinine levels and adjusts for age, sex, and race. The CKD–EPI equation employs a two-slope spline to model the relationship between eGFR and serum creatinine. The CKD–EPI equation performed better in validation studies than the MDRD equation, with less bias and greater accuracy, particularly at higher GFR levels.

Despite its advantages, the CKD–EPI equation has limitations. The samples used to develop and validate the equation included a limited number of elderly individuals and racial minorities, which may affect its generalizability to these populations. Nonetheless, the CKD–EPI equation's superior accuracy suggests it could replace the MDRD equation for routine clinical use, improving the precision of kidney function assessments and aiding in better management of chronic kidney disease.

In conclusion, the MDRD and CKD–EPI equations are valuable tools for estimating GFR from serum creatinine. The MDRD equation is simpler and well-suited for older and obese patients, while the CKD–EPI equation offers greater accuracy, particularly at higher GFR levels. Understanding the strengths and limitations of each method allows clinicians to choose the most appropriate equation for their patients, ultimately enhancing patient care.

Glomerular filtration rate, GFR, can be estimated from serum creatinine using diet modification in renal disease or MDRD formula and the chronic kidney disease–epidemiology collaboration or CKD–EPI equation.

These were developed based on serum creatinine and incorporate adjustments for age, sex, and race.

The MDRD equation does not require weight or height measurements and is normalized to the body surface area.

This method is more accurate for older and obese people than the healthy subjects.

The CKD–EPI equation was developed to estimate GFR more precisely, particularly when GFR levels were high.

It uses a two-slope spline to model the relationship between eGFR and serum creatinine.

In the validation data set, it demonstrated a tighter limit of agreement and outperformed the MDRD equation, which showed broader variability. CKD–EPI also showed less bias, especially at higher GFR levels.

CKD–EPI is also more accurate than MDRD and could replace it for routine clinical use.

However, the CKD–EPI samples have limited elderly and racial minority representation.