Type 1 Diabetes Mellitus: This is the most likely diagnosis due to the patient's age and the development of hyperglycemia. Type 1 diabetes is an autoimmune condition that often presents in young adulthood, characterized by the body's inability to produce insulin.

Type 2 Diabetes Mellitus: Although less common in this age group, type 2 diabetes is increasingly seen in younger individuals due to rising obesity rates and decreased physical activity. It is characterized by insulin resistance and impaired insulin secretion.
Gestational Diabetes: If the patient is pregnant, gestational diabetes should be considered. This condition is caused by insulin resistance during pregnancy and typically resolves after delivery.
Polycystic Ovary Syndrome (PCOS): PCOS is a common endocrine disorder in women of reproductive age, often associated with insulin resistance, which can lead to hyperglycemia.

Diabetic Ketoacidosis (DKA): A life-threatening complication of diabetes that can occur if hyperglycemia is left untreated. It is crucial to identify and manage DKA promptly to prevent serious consequences.
Cushing's Syndrome: A rare endocrine disorder caused by excess cortisol production, which can lead to hyperglycemia due to insulin resistance. Missing this diagnosis could lead to significant morbidity.
Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodes of hyperglycemia among other symptoms. Although rare, it is critical to diagnose due to its potential for severe complications.

Lipoatrophic Diabetes: A rare condition characterized by the loss of body fat, leading to insulin resistance and hyperglycemia.
Wolfram Syndrome: A rare genetic disorder that can cause diabetes, among other symptoms, due to pancreatic beta-cell dysfunction.
Steroid-Induced Diabetes: Hyperglycemia caused by the use of glucocorticoid medications, which can induce insulin resistance. This is less likely in a 23-year-old without a history of steroid use but should be considered if such a history exists.