Table.

Comparison of methods used to develop ethnicity coefficients for the Modification of Diet in Renal Disease Study equation.

	MDRD Study (87% whites, 13% African Americans) (2, 28)	Chinese Study(3)	Japanese Study(4)
Ethnicity Coefficient	1.0 in American whites, 1.21 in African Americans	1.23 in native Chinese	0.81 in native Japanese
External Validation	Performed well in several other studies of whites and African Americans with CKD (reasonably unbiased).(21)	Coefficient was inaccurate in a recent Chinese study.(11)	Ethnicity coefficient was similar (0.76) in a prior Japanese study.(5)
Serum Creatinine
Mean	2.1 mg/dl	2.0 mg/dl (not standardized)	1.6 mg/dl
Assay	Enzymatic (standardized)	Kinetic rate alkaline picrate (Jaffe) reaction	Enzymatic (standardized)
Calibration	Reference assay	Levels adjusted for calibration differences with the MDRD Study laboratory for the Chinese ethnicity coefficient, but not for the separate Chinese equation. This adjustment may not have been accurate.(11)	Levels were slightly lower than standardized assay used to develop MDRD Study equation. No adjustment was made.
Glomerular Filtration Rate
Mean	40 ml/min/1.73 m2	55 ml/min/1.73 m2	58 ml/min/1.73 m2
Exogenous marker	125I-Iothalamate with SC injection	99mTc-DTPA with bolus IV injection	Inulin with IV infusion over 2 hours
Clearance method	Urinary clearance with 4 consecutive urine collections by voluntary voiding (no bladder catheter) and 5 plasma samples after a 1 hour equilibrium period	Plasma clearance with dual plasma sampling method (plasma samples at 2nd and 4th hour)	Urinary clearance with 3 plasma and 3 urine samples over 2 hours
Patient factors (physiological state)	Fasting except for a 10 ml/kg oral water load (29)	Post-prandial and 300 to 500 ml oral water load (19)	Fasting except for 500 ml oral water load (30)
Study Population
Demographics	Mean age 51 years, 60% men	Mean age 50 years, 51% men	Mean age 51 years, 61% men
Body Surface Area	Mean 1.91 m2	Mean 1.7 m2	Mean 1.64 m2
Sample Size	1628 patients	684 patients	763 patients
Target sample	CKD as identified by an elevated SCr level (>1.4 mg/dL in men and >1.2 mg/dL in women) at 15 centers. Extensive exclusion criteria as is common in clinical trials.(31)	CKD as diagnosed by KDOQI guidelines (1) at 9 renal institutes at university hospitals. Persons with skeletal muscle atrophy, edema, heart failure, pleural effusions, or ascites excluded.	Mostly nephrology inpatients at 80 centers undergoing a kidney biopsy or education on life style changes.
Case Mix (top 4 etiologies)	Glomerular disease, polycystic kidney disease, hypertensive nephrosclerosis, other kidney disease or not specified	Primary or secondary glomerular disease, hypertension, obstructive kidney disease, renovascular disease	Chronic glomerulonephritis, miscellaneous, diabetes mellitus, and nephrosclerosis (kidney donors/recipients also included)
Statistical Methods	Regression of logarithmic GFR onto logarithmic SCr with a “African American compared with white ethnicity” indicator variable.	Measured GFR was regressed onto estimated GFR with the intercept forced to 0 and the slope as the Chinese coefficient.	Japanese coefficient calculated by minimizing the root-mean-squared error between measured GFR and estimated GFR.

Note: Conversion factors for units: serum creatinine in mg/dL to mol/L, x88.4; glomerular filtration rate in ml/min/1.73m² to ml/s/1.73m², multiply by 0.01667.

Abbreviations: CKD, chronic kidney disease; GFR, glomerular filtration rate; MDRD, modification of diet in renal disease; KDOQI, Kidney Disease Outcomes Quality Initiative, SC, subcutaneous; IV, intravenous; SCr, serum creatinine.