METHODS: AIM #1. Validation: (A) To establish feasibility, we will interact with VA primary care providers to solve logistical problems, and determine optimal screening strategies. (B) To assess test performance, we will (a) perform GCTs and measure A1c in ~1,800 patients, (b) evaluate OGTTs in all subjects, and (c) compare sensitivity, specificity, and ROC curves from GCT vs. A1c or "predictive model" screening in primary care to those in our GCRC studies. Availability of this dataset will also permit (d) subsequent management of diabetes/prediabetes to be evaluated relative to standardized guidelines. AIM #2. Costs: To evaluate impact, we will (a) capture the costs of diagnostic tests, staff effort, and patient time; (b) express cost per case identified from both VA health system and societal perspectives; and (c) compare GCT vs. alternative strategies with a wide range of assumptions about false-(+)/false-(-) costs to reflect downstream cost implications of test imperfections. Engagement with this process will also provide (d) for those study patients with prediabetes who go on to develop diabetes, an opportunity to explore VA resource use and costs before and after the diagnosis of diabetes. This will provide preliminary data for subsequent proposals to compare resource use and costs vs. those of other VA patients who are newly diagnosed with diabetes in settings where there is no screening for prediabetes.