Methodological considerations with the use of urine samples for assessment of mercury excretion and markers of renal damage

Objective: To provide recommendations for design and analysis of studies using urine specimens to evaluate renal function or mercury excretion in children. Methods: An analysis of mercury, albumin, gamma-glutamyl transpeptidase (gamma-GT) and N-acetyl-beta-D-glucosaminidase (NAG) concentrations was carried out. Results: Mercury concentration and creatinine-corrected renal markers were higher in daytime compared with overnight samples. Excretion rates increased with urinary flow rate. gamma-GT and NAG concentrations decreased with storage time at -20 degrees C. Differences by age, sex and race were noted. Conclusions: We recommend use of these creatinine-corrected markers and collection of timed overnight urine samples, stored at -70 degrees C, with control for urinary flow rate, age, sex and race in statistical models.