Microalbuminuria is a mild urinary albumin elevation and is associated with cardiovascular disease. Urinary albumin/creatinine ratio is recommended for microalbuminuria assessment, because it reflects urinary albumin excretion. Muscular mass could affect albumin/creatinine ratio, because urinary creatinine reflects muscular mass. The study investigated high albumin/creatinine ratio attributed to low urinary creatinine without microalbuminuria. The Gubbio Population Study for ages 45 to 64 collected data on weight, skinfold, urinary albumin, urinary creatinine, and coronary heart disease. Weight and skinfold thickness were used to calculate fat and nonfat mass and urinary creatinine as a marker of muscular mass. Microalbuminuria was defined as urinary albumin of 20 to 199 microg/min and high albumin/creatinine ratio as a ratio of 17 to 250 microg/mg in men and of 25 to 355 microg/mg in women. Persons with macroalbuminuria (urinary albumin > or =200 microg/min) were excluded to focus analyses on microalbuminuria. Coronary heart disease was defined by ECG and questionnaire. The target cohort consisted of 1623 men and women, ages 45 to 64. Prevalence was 8.5% for high albumin/creatinine ratio (n=138), 4.3% for microalbuminuria (n=69), 5.2% for high albumin/creatinine ratio without microalbuminuria (n=85), and 1.0% for nonhigh albumin/creatinine ratio with microalbuminuria (n=16). High albumin/creatinine ratio without microalbuminuria was inversely associated with nonfat mass and urinary creatinine (P<0.04). Compared with persons with a nonhigh albumin/creatinine ratio, coronary heart disease was more prevalent in persons with a high albumin/creatinine ratio and microalbuminuria (18.9% and 7.1%; P=0.002), not in persons with a high albumin/creatinine ratio without microalbuminuria (8.2% and 7.1%; P=0.706). A high albumin/creatinine ratio in persons with low muscle mass indicates low urinary creatinine more often than microalbuminuria and cardiovascular disease.