D3-Hydroxybutyrate (D-3HB) is a ketone body primarily produced in the liver during fatty acid metabolism. It's a key energy source, particularly during periods of fasting, prolonged exercise, or carbohydrate restriction. Clinically, D-3HB is often measured to assess ketone levels in conditions like diabetic ketoacidosis, where elevated ketone bodies can indicate a severe imbalance. The D-3HB test is more specific and stable than traditional urine ketone tests, making it reliable for monitoring metabolic health and energy regulation.