The ratio of the concentration of a biomarker to urinary creatine is often used to adjust biomarker concentration for urinary dilution. An implicit assumption of this method is that the ratio will be independent of urinary creatinine, indicating that the biomarker has been adequately adjusted for urinary dilution. When this is not the case, an alternative adjustment based on multiple regression can improve the adjustment for urinary dilution. We investigated the methodological assumptions and implications of the ratio adjustment method and compared it to an adjustment based on multiple regression. Graphical illustrations of the regression adjustment were used to show how the two adjustment methods are related. The multiple regression method was applied to the adjustment of alanine aminopeptidase (AAP), albumin (ALB), N-acetyl-B-D-glucosamindase (NAG), and retinol-binding protein (RBP) obtained from urine samples of 1331 healthy subjects aged 6 months through 74 years. The adequacy of the ratio adjustment was assessed by estimating the beta coefficient in a regression of the log biomarkers on log creatinine and determining whether the estimated confidence interval contained the value 1.0. The adjustment based on multiple regression improved upon the ratio adjustment of biomarker concentration for urinary dilution. These results indicate that ratio adjustments might be inadequate for properly adjusting biomarker concentrations for urinary dilution.
Learning Objectives: N/A
Keywords: Indicators, Methodology
Presenting author's disclosure statement:
Organization/institution whose products or services will be discussed: None
I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.