title: Coefficient of Variation, Signal-to-Noise Ratio, and Effects of Normalization in Validation of Biomarkers from NMR-based Metabonomics Studies.
abstract: A primary goal of metabonomics research is biomarker discovery for human diseases based on differences in metabolic profiles betweenhealthyanddiseasedpatient populations. One of the most significant challenges in biomarker discovery is validation, which implicitly depends on the coefficient of variation (CV) associated with the measurement technique. This paper investigates how the CV of metabolite resonances measured by nuclear magnetic resonance spectroscopy (NMR) depends on signal-to-noise ratio (SNR) and normalization method. CVs were calculated for NMR resonance peaks in a series of NMR spectra of five synthetic urine samples collected over an eight-month period. An inverse correlation was detected between SNR and CV for all normalization methods. Small peaks with SNR<15 tended to have larger CVs (15-30%) compared to peaks with the highest SNR>150, which typically had smaller CVs (5-10%). The inverse relationship between CV and SNR roughly obeyed a log10dependence.Quotient normalization (QN)tended to produce smaller CVs for smaller peaks, but larger CVs for the strongest peaks in the data, compared tono normalization, normalization to total intensity (NTI)ornormalization to an internal standard (NIS). Consequently,quotient normalizationappears optimal for validating low concentration metabolites.NTI or NISappear superior to QN for samples that have very small variation in total signal intensity. While the inverse relationship between CV and log10(SNR) did not strictly hold for all metabolites, weaker concentration metabolites will likely require more rigorous validation as potential biomarkers since they tend to have poorer reproducibility.
authors.affiliation: Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Wang
authors.affiliation: Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Goodpaster
authors.affiliation: Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kennedy
keywords: Biomarker Validation; Coefficient of Variation; Metabolomics; Metabonomics; Nuclear Magnetic Resonance