The severity of hyperglycemia at hospital admission is associated with COVID-19 mortality in a graded manner. Relative to patients with normal blood glucose, those with admission hyperglycemia, pre-existing (known) diabetes, or newly diagnosed diabetes show progressively elevated mortality, with newly diagnosed diabetes carrying the highest risk—exceeding that of known diabetes. Evidence from hospitalized cohorts in Wuhan, China and North-East Italy indicates that acute glucose dysregulation, not merely a prior diabetes diagnosis, is a key driver of severe COVID-19 outcomes.