Trends in the levels of urine and serum creatinine: data from NHANES 2001-2014.

Data from the National Health and Nutrition Examination Survey were used to study trends for urine and serum creatinine over 2001-2014 for those aged ≥20 years. In the absence of chronic kidney disease, levels of urine creatinine decreased for the total population, for those aged 20-29, 50-59, and ≥70 years, for males, and for Mexican Americans and other race/ethnicities. Levels of serum cotinine also exhibited a decreasing trend over 2001-2014 for the total population, for those aged 20-29 and 40-49 years, for females, and for non-Hispanic whites and Mexican Americans. In general, levels of serum creatinine and urine creatinine were positively correlated for chronic kidney disease stages 1-3 and negatively correlated for chronic kidney disease stages 4 and 5.