Creatinine corrections for estimating children's and adult's pesticide intake doses in equilibrium with urinary pesticide and creatinine concentrations

A urine contaminant concentration per se has uncertain meaning for human health because of dilution by hydration. However, the estimation of the health-related daily intake dose of pollutant (mg/kg/day) that equilibrates with a spot urinary concentration of a pesticide residue or metabolite, or other analyte, can be made using creatinine-corrected toxicant levels (mg analyte/mg creatinine) multiplied by an estimate oft he subjects' expected creatinine excretion rates (mg creatinine/kg/day). The objective was to develop a set of equations predicting a person's expected daily creatinine excretion (mg/kg) as a function of age, gender, race and morphometry, from birth to old age. We review the creatinine excretion literature where infants, children and adults provided 24 h total urine samples for creatinine analysis. Equations are developed for infants (<= 3 years), children (3-18 years) and adults (>= 18 years) that match at 3 and 18 years. A series of equations that estimate daily creatinine excretion (mg/day) are developed that are piecewise continuous from birth through infancy through adolescence and through adulthood for males and females, and Black and White races. Complicating factors such as diet, health status and obesity are discussed. We propose that these equations, with caveat, can now be used with measured urine concentrations to consistently estimate the corresponding equilibrium intake doses of toxicants at ages from birth to 92 years for the healthy non-obese. We recommend that this system of equations be considered for future development and reporting of applied doses in mg/kg/day of pollutants and toxicants that are measured in urine samples, as in the National Health and Nutrition Examination Survey.