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Background/Aims: Predictors of microalbuminuria in the early stage of hypertension are not well known. We did a prospective study to investigate whether glomerular hyperfiltration assessed from serum cystatin C predicts development of microalbuminuria in hypertension. Methods: We assessed 101 treatment-naive subjects screened for stage 1 hypertension and followed-up for a median 3.1 years. Cystatin C was measured at entry and glomerular filtration rate was estimated using the Hoek formula (CystGFR). Urinary albumin and ambulatory blood pressure were measured at entry and during the follow-up. Results: Subjects in the top CystGFR tertile (>115 ml/min/1.73m2) were leaner (p = 0.002) and developed microalbuminuria more frequently (p = 0.02) than the rest of the group. In univariate Cox regression, CystGFR was associated with future microalbuminuria (hazard ratio, 1.06, 95% confidence interval (CI), 1.02–1.10, p = 0.001). After controlling for baseline albumin excretion rate and several confounders, CystGFR remained a significant predictor of microalbuminuria development (hazard ratio, 1.19, 95% CI, 1.03–1.37, p = 0.019). The association between future microalbuminuria and creatinine clearance or glomerular filtration rate estimated with the Cockroft-Gault or the Modification of Diet in Renal Disease formula did not attain the level of statistical significance in this sample. Conclusions: The present findings indicate that CystGFR is more sensitive than creatinine clearance or estimated glomerular filtration rate for predicting microalbuminuria development in the early stage of hypertension and confirm that hyperfiltration precedes microalbuminuria in this clinical entity. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]