Table 1.

Comparison of bedside equations used to estimate kidney function

VariablesMeasuresStudy Population DemographicsStudy Population Kidney FunctionAdvantagesLimitations
CG (1976)
 Age, SCr, sex, weighteCrCl, ml/minn=236 (subpopulation of 534 patients on the basis of duplicate 24-h mCrCl being within 20%)Average CrCl approximately 78 ml/minConvenient to useEstimates creatinine clearance as a surrogate for GFR
Mean age 53 yr, 24% >70 yr, 96% menModel used for determining recommendations for drug dose adjustment for kidney functionCorrelation between mCrCl and eCrCl R2=0.69
Veterans Hospital patientsUses 24-h urine collection as standard
Does not use standardized SCr laboratory values, and eGFRs before standardization were 10%–20% higher
Underestimates at severely reduced kidney function
Less accurate in patients with extremes of age or body size
Adjustment for sex is empirical
MDRD (2006)
 Age, SCr, sex, raceeGFR, ml/min per 1.73 m2n=1628Average GFR 39.8 ml/min per 1.73 m2P30 values range 73%–93%Underestimates at normal and mildly reduced kidney function (>60 ml/min)
Mean age 50.6 yrFew patients with GFR>90 ml/min per 1.73 m2Uses iothalamate clearance as standardNot used for determining most kidney drug-dosing recommendations
60% menMDRD-4 uses standardized SCr laboratory values
88% whiteImproves on CG estimation at GFR<60 ml/min per 1.73 m2
6% diabetic
Patients with CKD
CKD-EPI (2009)
 Age, SCr, sex, raceeGFR, ml/min per 1.73 m2n=5253Mean GFR 68 ml/min per 1.73 m2P30=91.5% with cystatin CNot used for determining most kidney drug-dosing recommendations
Mean age 43 yr, 13% >65 yrUses iothalamate clearance as standard
58% menUses standardized SCr laboratory values
63% white, 32% black, 1% AsianImproves on MDRD estimation at GFR>60 ml/min per 1.73 m2
Patients with CKD
  • CG, Cockcroft–Gault; eCrCl, estimated creatinine clearance; mCrCl, measured creatinine clearance; CrCl, creatinine clearance; SCr, serum creatinine; MDRD, Modification of Diet in Renal Disease; P30, percentage of estimates that were within 30% of the reference value; CKD-EPI, Chronic Kidney Disease Epidemiology Collaboration.