Serum metabolomics associated with NF. (A) Distribution of serum metabolites into pathways. (B) Volcano plot showing the magnitude and significance of metabolomics changes within 24 hours before NF. High-risk (preceding NF within 24 hours) and low-risk samples (not preceding NF within 24 hours) were compared. Points to the right (left) of the vertical line (no change) represent metabolites that were increased (decreased) before NF. Select metabolites of interest in this work are labeled (the orange circle representing p-cresol sulfate is nearly completely hidden behind 2 green circles). The horizontal lines represent q = .05 and q = .1, above which the metabolites are statistically significant according to the corresponding threshold. p values from Welch’s t-test were corrected for multiple testing to derive the q values. (C) Distribution of metabolites with q < .1 in (B) into pathways. (D) Overrepresentation analysis using subpathways. Metabolites with q < .05 in (B) were considered for overrepresentation of their subpathways using a hypergeometric test with a corrected P value threshold of .05. Each central node represents an overrepresented subpathway, and the peripheral nodes connected to the central node represent the metabolites within that subpathway that are significant in (B). The number of these metabolites in each overrepresented subpathway is proportional to the size of the central node. The complete list of metabolites is provided in supplemental Data 1.