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, γ-glutamyl transpeptidase (γ-GT), N-acetyl-β-d-glucosaminidase (NAG), α₁-microglobulin (α1M), 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, γ-GT, NAG, and α1M 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 γ-GT increased significantly with age. Albumin and γ-GT concentration and excretion (milligrams per gram of creatinine or units per gram creatinine) were significantly greater for girls compared with boys. α1M 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 γ-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 α1M 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.

Index Words: Age, sex, race, renal damage, children, albumin, γ-glutamyl transpeptidase, N-acetyl-β-d-glucosaminidase, α₁-microglobulin