Renal albumin excretion in healthy young adults and its association with mortality risk in the US population.

Background: Current classification systems do not specify a healthy normal range for urinary albumin excretion. Occult microvascular disease induced by a Western lifestyle may mean that normal values for apparently healthy adults exceed optimal levels defined by mortality risk.

Methods: Using a national population sample [the US Third National Health and Nutrition Examination Survey (NHANES III) cohort; n = 11 887], the distributions of albumin:creatinine ratio (ACR) and fractional excretion of albumin (FEalb) were studied in healthy young adults [ages 20-40 years, without cardiovascular disease (CVD) or risk factors]. The threshold for mortality risk prediction in the whole adult population sample was then studied across ACR/FEalb categories corresponding to quartiles for healthy young adults.

Results: ACR quartiles for healthy young adults were 2.7, 4.2 and 5.9 mg/g in men and 3.8, 6.2 and 9.8 mg/g in women. Increases in ACR below the medians for healthy young adults were not associated with increased mortality or with cardiovascular risk factors when tested in the whole adult population. Increases above this threshold were independently associated with mortality risk [hazard ratio 1.2 (95% confidence interval 1.1-1.4) and 1.8 (1.6-2.0) for Quartiles 3 and 4, respectively]. The prevalence of an optimal ACR below the mortality risk threshold was <25% in the setting of diabetes, hypertension, age >70 years or CVD. Using FEalb to define quartiles of albuminuria gave the same findings.

Conclusion: Based on mortality risk in the whole adult population, there is an optimal range of albumin excretion (ACR < 6 mg/g and 4 mg/g for women and men, respectively). However, only half of even apparently healthy young US adults fall within this range.