Abstract Currently accepted clinical standards for assessing kidney function include the measurement of creatinine for calculating estimated glomerular filtration rates (eGFR) and albumin to creatinine ratios. However, creatinine, a product of muscle creatine metabolism, is an imperfect proxy for renal function because it is subject to non-renal interferences. There is an unmet need for extremely sensitive and precise biomarkers for evaluating renal function in patients given that acute kidney injury (AKI) and chronic kidney disease (CKD) are linked to high mortality, morbidity, and contribute considerably to health care expenditures.Myo-inositol oxygenase (MIOX) is a novel biomarker limitedly expressed in the proximal renal tubules. MIOX concentrations are elevated in mice with renal injury and in critically ill patients with acute kidney injury (AKI), and increases are observed 54 h prior to changes in serum creatinine are observed. Importantly, MIOX facilitates the conversion of myo-inositol to glucuronic acid. We developed a robust LC-MS/MS method to quantify myo-inositol in human plasma and serum, hypothesizing that following renal injury (acute and chronic), plasma concentrations of myo-inositol will increase, and will correlate with increases in serum creatinine concentrations.In patients with stable renal function, the central 95% distribution of plasma myo-inositol concentrations was 16.61–44.2 µM (Median 27.7 µM, 95% CI: 26.7–28–7). No sex-based differences in plasma myo-inositol were observed. We also observed excellent correlation between plasma myo-inositol and serum creatinine concentrations (r = 0.84, 95% CI: 80–88), as well as excellent sensitivity (99%) and specificity (100%) at a myo-inositol concentration of 50.22 µM for differentiating patients with stable kidney function from those with CKD. Patients with CKD exhibited higher plasma myo-inositol concentrations (P value < 0.0001) with a central 95% percentile of 51.2–309.1 µM (Median 104.1 µM, 95% CI: 92.3–113.6).These results imply that myo-inositol concentrations increase in accord with renal tubular injury and MIOX buildup in patients with kidney dysfunction, making it a potential biomarker for renal impairment.