METHODS Although Caribbean people have been a lesser-studied ethnic group than other populations, they have a high burden of hypertension and renal disease. Because Caribbean people have a greater muscle mass than Caucasians, this study examined the accuracy of creatinine-based estimates (creatinine clearance; C(cr) and Cockcroft-Gault formula; C-G Cl) of glomerular filtration rate (GFR) in 38 Caribbeans who were matched for age, gender, and GFR, with 38 Caucasian subjects. Patients were considered black Caribbean if at least one of two parents was of black Caribbean origin. GFR values ranging from 5 to 140 ml/min/1.73 m(2) were measured by inulin clearance. Results were compared using linear correlations and the Bland and Altman methodology to provide better estimates of value dispersion. RESULTS Correlation coefficients between C-G Cl and GFR were highly significant in both black Caribbean subjects (r=0.83, P<0.001) and Caucasians (r=0.84, P<0.001). Similar coefficients were obtained between C(cr) and GFR (r=0.89, P<0.001 and r=0.90, P<0.001, respectively). In spite of these strong correlations, the Bland and Altman representation highlighted huge intra-individual variations in GFR estimation by C-G Cl and by C(cr) in both ethnic groups. The underestimation of GFR by C-G Cl was significant in black Caribbeans (-8.6+/-20 ml/min/1.73 m(2), P<0.001) but not in Caucasians (-5.6+/-20.7 ml/min/1.73 m(2)). C(cr) overestimation of GFR was significant both in Caribbeans (8.7+/-16.8 ml/min/1.73 m(2), P<0.001) and in Caucasians (7.2+/-15.7 ml/min/1.73 m(2), P<0.01). CONCLUSIONS The C-G formula for estimating GFR yields similar clinical values in black Caribbeans and in Caucasians, but the same limitations were observed in both ethnic groups.