FGF23 and acute kidney injury: Day 1 total FGF23 concentrations were significantly higher in subjects with Day 3 AKI than in those without Day 3 AKI (median 944 [IQR 357, 6556] RU/ml vs. median 166 [IQR 89, 466] RU/ml, p<0.001) (Fig 2A).