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

The MDRD (modification of diet in renal disease) equation estimates GFR from serum creatinine without requiring weight or height measurements. It is normalized to a body surface area of 1.73 m², the average adult surface area, and incorporates adjustments for age, sex, and race. This method is particularly accurate for older and obese individuals.

The CKD-EPI equation was developed to estimate GFR more precisely, especially at higher GFR levels. It uses a two-slope spline to model the relationship between eGFR and serum creatinine, demonstrating tighter limits of agreement and less bias than MDRD in validation studies. CKD-EPI's superior accuracy suggests it could replace MDRD for routine clinical use.

The MDRD equation does not require weight or height measurements, eliminating the complexity of obtaining these data in obese individuals. By normalizing to body surface area, it provides more accurate GFR estimates in obese and older populations compared to healthy subjects, simplifying the assessment of kidney function.

Both the MDRD and CKD-EPI equations adjust for age, sex, and race when estimating GFR from serum creatinine. These demographic factors significantly influence the relationship between serum creatinine levels and actual kidney filtration capacity, making them essential variables for accurate GFR estimation.

Although the CKD-EPI equation offers superior accuracy, the samples used to develop and validate it included limited representation of elderly individuals and racial minorities. This limited diversity may affect the equation's generalizability to these specific populations, potentially reducing its accuracy in these groups.

The MDRD equation performs well across various GFR levels but shows broader variability. The CKD-EPI equation demonstrates superior performance particularly at higher GFR levels, with less bias and greater accuracy. This makes CKD-EPI more suitable for patients with better-preserved kidney function.

Serum creatinine is a readily measurable marker of kidney function that correlates with glomerular filtration rate. Both MDRD and CKD-EPI equations use serum creatinine as their primary variable because it is practical, cost-effective, and widely available in clinical settings, making GFR estimation accessible for routine patient assessment.