EVALUATION OF SERUM CREATININE FOR ESTIMATING GLOMERULAR-FILTRATION RATE IN AFRICAN-AMERICANS WITH HYPERTENSIVE NEPHROSCLEROSIS - RESULTS FROM THE AFRICAN-AMERICAN STUDY OF KIDNEY-DISEASE AND HYPERTENSION (AASK) PILOT-STUDY

Measurement of GFR is considered the standard for estimating renal fun ction. However, standardized accurate GFR methodology is expensive and cumbersome; therefore, estimates of GFR based on serum creatinine con centration have been employed. The purpose of the study presented here was to assess the accuracy and precision of using serum creatinine me asurements to estimate GFR in the screenee cohort of The African-Ameri can Study of Kidney Disease and Hypertension (AASK) Pilot Study. GFR w as estimated by four methods: 100/serum creatinine, Cockcroft-Gault eq uation, creatinine clearance from 24-h urine collection, and a new reg ression equation derived from the pilot study data. These methods were compared with renal clearance of I-125-iothalamate GFR (GFR1) in 193 hypertensive (diastolic blood pressure greater than or equal to 95 mm Hg) African-American screenees (142 men, 51 women). A second GFR (GFR2 ) was performed in 98 screenees who were eligible (GFR1 25-70 mL/min p er 1.73 m(2)) for the pilot study. Accuracy was assessed by the differ ence of I-125-iothalamate GFR-estimated GFR (Delta GFR), and precision was estimated from the combined root mean squared error (CRMSE) and t he coefficient of determination (r(2)) The results for accuracy (+/- S D) and precision were as follows: (1)100/Scr, Delta GFR = -0.76 +/- 16 .5, CRMSE = 16.5, r(2) = 0.69; (2) Cockcroft- Gault, Delta GFR = 9.56 +/- 14.9, CRMSE = 17.7, r(2) = 0.66; 3) 24-h creatinine clearance, Del ta GFR = 0.79 +/-i 20.7, CRMSE = 20.7, r(2) = 0.49; 4) New equation De lta GFR = -0.08 +/- 12.8, CRMSE 12.7, r(2) = 0.75. In comparison, a se cond GFR (GFR2, N = 98) had Delta GFR = 1.36 +/- 8.48, CRMSE 8.6, r(2) = 0.75. Estimates based on 100/SCr and the new equation were the most precise. It was concluded that GFR estimated by serum creatinine is s uperior to outpatient 24-h urine creatinine clearance in this populati on. Serum creatinine values can be used to provide a reasonably accura te estimate of GFR in hypertensive African Americans.