Patient presents with classic symptoms of type 1 diabetes mellitus, including polyuria, polydipsia, polyphagia, and recent unexplained weight loss.  The patient reports increased frequency of urination, excessive thirst, and constant hunger despite increased food intake.  Onset of symptoms has been gradual over the past few weeks.  Family history is negative for type 1 diabetes but includes type 2 diabetes mellitus in a maternal grandparent.  Physical examination reveals dry mucous membranes.  Initial point-of-care blood glucose is significantly elevated.  Laboratory findings confirm hyperglycemia, and the presence of autoantibodies such as islet cell cytoplasmic autoantibodies (ICA), glutamic acid decarboxylase autoantibodies (GADA), or insulin autoantibodies (IAA) supports the diagnosis.  HbA1c is elevated, indicating chronic hyperglycemia.  Urinalysis reveals glycosuria and ketonuria, suggestive of inadequate insulin production.  Differential diagnoses considered include type 2 diabetes mellitus and maturity-onset diabetes of the young (MODY).  However, the patient's age, clinical presentation, and laboratory results are more consistent with type 1 diabetes mellitus.  The patient has been educated on diabetes management, including insulin therapy, blood glucose monitoring, carbohydrate counting, and the importance of regular follow-up with an endocrinologist.  An insulin regimen, including basal and bolus insulin, has been initiated.  Dietary counseling has been provided, and the patient has been referred to a certified diabetes educator for comprehensive diabetes self-management education and support.  The patient understands the importance of recognizing and treating hypoglycemia and hyperglycemia.  Follow-up appointment scheduled in two weeks to assess glycemic control and adjust insulin therapy as needed.  Diagnosis: Type 1 diabetes mellitus (ICD-10-CM E10.9).