The 2020 CDC national diabetes statistics report identified that 34.2 million Americans, or 10.5% of the population had diabetes in 2018. It is estimated that over the course of their lifetime up to a third of these people with diabetes will develop a diabetic foot ulcer (DFU). The five-year mortality and direct costs of care for people with diabetic foot complications are comparable to cancer. Approximately 40-60% of nontraumatic lower limb amputations worldwide are caused by diabetic complications, and 80% of these amputations follow DFU. In patients with hard-to-heal DFUs, treatment with multiple therapies is often necessary to manage stubborn wounds. The current DFU treatment algorithm uses failure to improve (>50% wound area reduction) after four weeks of standard of care (SoC) therapy to make a clinical decision on changing the therapy. The lack of objective early indicators of wound healing outcomes handicaps DFU care strategy. Biomarkers that predict non- healing (i.e., refractory to SoC) would provide an objective basis for rationally adopting alternate treatment regimen to wound care providers in a timely manner. This proposal rests on our premise that non-healing diabetic wounds would suffer from metabolic impairments which in turn would be reflected by changes in metabolites contained in wound fluids (WF). A metabolomics approach was used to screen 578 metabolites from 161 WF from chronic wound patients. Of all these metabolites, ONE PARAMETER emerged as a robust predictor of non- healing: low Cysteine (Cys)/Cystine (CysS). A prospective preliminary study on DFU patients (N=24) showed that low Cys/CysS in WF predicts non-healing. A point-of-care microtiter-plate (standard hospital assay platform) based test was used. Because the proposed work seeks to establish Cysteine Redox as a biomarker of non- healing or Open wound, the study is named CREDO. The R61 preparatory phase is named 2CREDO (towards CREDO), and the R33 phase is referred to as CREDO. Aim 1: Validate the use DFU wound fluid low Cys/CysS ratio (<3.43 cut-off) as a primary biomarker to predict non-healing of DFU. Aim 2: Develop a complete clinical protocol to validate the use of Cys/CysS ratio in wound fluids to predict the healing of adult DFU. Aim 3: Conduct a multi-center clinical study of diabetic foot ulcer patients to perform detailed validation of wound fluid based Cys/CysS ratio as a biomarker to predict diabetic foot ulcer healing. Aim 4: Initiate discussions with FDA to establish Cys/CysS as a clinical biomarker to predict DFU healing. The proposed work will be conducted as ancillary Study of the current NIDDK Diabetic Foot Consortium (DFC) who have approved feasibility of our protocol.