The objective of this study was to assess the relationship between urinary albumin excretion (UAE) and GF across the spectrum of the glucose metabolism abnormalities in a large population of patients with hypertension. The Microaluminuria en Pacientes con Glucemia Basal Alterada (MAGAL) is a multicenter, cross-sectional study that was carried out by 1723 primary care physicians. A total of 6227 patients with essential hypertension (in three groups: [1] normal fasting glucose <100 mg/dl, [2] impaired fasting glucose > or =100 to 126 mg/dl, and [3] type 2 diabetes) were analyzed in this substudy. GFR was estimated by using the Modification of Diet in Renal Disease (MDRD) abbreviated equation. A single first-morning urine albumin/creatinine ratio was measured using Bayer reagent strip Microalbustix, a semiquantitative method. Abnormal UAE was defined as an albumin/creatinine ratio > or =3.4 mg/mmol (equivalent to > or =30 mg/g). The prevalence of abnormal UAE, > or =3.4 mg/mmol, increased across the spectrum of glucose abnormalities: 39.7, 46.2, 48.6, and 65.6% for normoglycemic, low-range, and high-range impaired fasting glucose and diabetes, respectively. UAE was positively related to SBP (P = 0.003) and inversely to GFR (P < 0.001). Renal insufficiency (GFR <60 ml/min per 1.73 m2) was present in 21.8% of the patients, more frequently older patients, women, and those with diabetes. The factors that were related to renal insufficiency were UAE > or =3.4 mg/mmol (odds ratio 1.86; 95% confidence interval 1.60 to 2.17) and diabetes (odds ratio 1.62; 95% confidence interval 1.29 to 2.04). There is a close relationship between abnormal UAE and renal insufficiency in essential hypertension. This is more marked in patients with diabetes and moderate in patients with high-range impaired fasting glucose.