For most patients, experiencing several weeks of polyuria, polydipsia, fatigue, and significant weight loss may indicate the presence of diabetes. Furthermore, adults displaying the phenotypic appearance of type 2 diabetes (particularly those who are obese and not initially insulin-requiring), may have islet cell autoantibodies, suggesting autoimmune-mediated β cell destruction and a diagnosis of latent autoimmune diabetes of adults (LADA). The categorization of glucose homeostasis is based on fasting blood glucose and glucose levels following an oral glucose challenge. These categories include:

1. Normal glucose homeostasis: fasting plasma glucose < 5.6 mmol/L (100 mg/dL)
2. Impaired fasting glucose (IFG): 5.6–6.9 mmol/L (100–125 mg/dL)
3. Impaired glucose tolerance (IGT): glucose level between 7.8 and 11.1 mmol/L (140 and 199 mg/dL) 120 min after ingestion of 75g liquid glucose solution
4. Diabetes mellitus: fasting plasma glucose ≥ 7.0 mmol/L (126 mg/dL), 2-hour plasma glucose ≥ 11.1 mmol/L (200 mg/dL) after a 75g oral glucose tolerance test, or an HbA1c ≥ 6.5%.

The American Diabetes Association (ADA) and the World Health Organization (WHO) have established criteria for diagnosing diabetes based on fasting blood glucose, glucose response to an oral glucose challenge, or the level of HbA1c, also known as A1c. IFG and IGT signify an increased risk of progression to type 2 diabetes and are associated with a higher risk of cardiovascular disease. Many individuals with type 2 diabetes are asymptomatic at the time of diagnosis. The ADA recommends widespread screening for type 2 diabetes in adults with specific risk factors such as age over 45 years, high body mass index, physical inactivity, hypertension, and family history of type 2 diabetes, among others. Early diagnosis and treatment of type 2 diabetes can help delay diabetes-related complications and reduce the burden of the disease.

Untreated diabetes can lead to severe metabolic disturbances, including diabetic ketoacidosis and a hyperglycemic hyperosmolar state, which require immediate medical attention. Chronic end-organ effects of diabetes encompass microvascular and macrovascular complications. Evidence from clinical trials suggests that most diabetes-related complications can be prevented, delayed, or reduced by effectively managing glucose levels. In conclusion, understanding the symptoms, diagnosis, and potential complications of diabetes is crucial for timely intervention and effective management of the condition.