The effect of age, sex, and race on urinary markers of kidney damage in children

Background: The aim of this study is to examine the effects of age, sex, and race on the excretion and concentrations of albumin, gamma-glutamyl transpeptidase (gamma-GT), N-acetyl-beta-D-glucosaminidase (NAG), alpha(1)-microglobulin (alpha 1M), and creatinine in children. Study Design: Secondary analysis of a clinical trial, The New England Children's Amalgam Trial, which examined effects of amalgam dental fillings. Setting & Participants: 534 children aged 6 to 10 years at baseline were recruited from Boston, MA, and rural Maine. Predictors: Age, sex, and race. Outcomes & Measurements: Urine samples were collected annually for 5 years and analyzed for creatinine, albumin, gamma-GT, NAG, and alpha 1M concentrations. Repeated-measures analysis of covariance was used to model effects of age, sex, and race on these values, as well as calculated excretion rates. Results: All measures of creatinine and gamma-GT increased significantly with age. Albumin and gamma-GT concentration and excretion (milligrams per gram of creatinine or units per gram creatinine) were significantly greater for girls compared with boys. alpha 1M concentration and creatinine excretion were greater for boys compared with girls. Creatinine concentration was significantly greater for blacks than for whites and Hispanics. Creatinine excretion and all gamma-GT levels were significantly greater for blacks and Hispanics compared with non-Hispanic whites. Limitations: The study population, recruited for a clinical trial, was of lower socioeconomic status than the general population. The high limit of detection for alpha 1M resulted in a majority of samples less than the detection limit. Conclusions: We recommend considering age, sex, and race in the interpretation of urinary markers. It also is recommended that epidemiological studies and clinical trials account for age, sex, and race in statistical models comparing urinary markers of kidney damage.