Diabetes overview

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“Diabetes” covers several major areas:

Definition and types: type 1, type 2, gestational diabetes, and less common secondary forms
Causes and risk factors
Symptoms and warning signs
Diagnosis: fasting glucose, HbA1c, oral glucose-tolerance testing
Treatment: nutrition, activity, monitoring, tablets, insulin
Acute emergencies: hypoglycemia, diabetic ketoacidosis, hyperosmolar state
Long-term complications: eye, kidney, nerve, heart, foot, and stroke risk
Prevention and screening

Brief overview: Diabetes mellitus is a condition in which blood glucose remains too high because the body produces too little insulin, does not respond adequately to insulin, or both. Type 1 diabetes results from autoimmune destruction of pancreatic beta cells and requires insulin. Type 2 diabetes, the most common form, is characterized chiefly by insulin resistance with gradual loss of insulin production.

Common symptoms include thirst, frequent urination, increased hunger, fatigue, blurred vision, unexplained weight loss, recurrent infections, or slow-healing wounds. Type 2 diabetes may cause no symptoms for years. Persistent high glucose can damage small and large blood vessels, affecting the eyes, kidneys, nerves, heart, brain, and feet.

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Summarize diabetes diagnosis and treatment options

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"Diabetes Mellitus, Type 2"[MeSH Terms] AND treatment

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ADA Standards of Care 2026 diabetes diagnosis classification pharmacologic treatment

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https://diabetesjournals.org/care/article/49/Supplement_1/S2…

Diagnosis

Diabetes is diagnosed using one of these tests:

Test	Diabetes threshold
HbA1c	≥6.5%
Fasting plasma glucose, after at least 8 hours fasting	≥126 mg/dL (≥7.0 mmol/L)
2-hour plasma glucose after a 75-g oral glucose tolerance test	≥200 mg/dL (≥11.1 mmol/L)
Random plasma glucose with classic symptoms or hyperglycemic crisis	≥200 mg/dL (≥11.1 mmol/L)

If there are no clear symptoms or hyperglycemic crisis, an abnormal result should usually be confirmed on a separate day with the same or another diagnostic test. The current ADA diagnostic criteria use HbA1c or plasma glucose testing.

Prediabetes is usually:

HbA1c: 5.7% to 6.4%
Fasting glucose: 100 to 125 mg/dL
2-hour OGTT glucose: 140 to 199 mg/dL

HbA1c reflects approximate average glucose over the preceding 2 to 3 months. It can be unreliable in some situations, including certain hemoglobin disorders, recent blood loss or transfusion, pregnancy, and conditions that substantially alter red-cell survival.

Tests that help classify the type may include pancreatic autoantibodies and C-peptide, especially where type 1 diabetes, latent autoimmune diabetes in adults, or monogenic diabetes is possible.

Treatment options

Treatment is individualized by diabetes type, glucose level, weight goals, kidney function, cardiovascular disease, heart failure, risk of hypoglycemia, cost, and patient preference.

Type 1 diabetes

Insulin is essential. Usual approaches are:

Multiple daily injections: long-acting basal insulin plus rapid-acting mealtime insulin
Insulin pump therapy
Continuous glucose monitoring, where available
Education on carbohydrate counting, insulin adjustment, sick-day rules, and prevention/treatment of hypoglycemia

Rapid-acting plus long-acting insulin analogs provide a more physiologic replacement regimen in type 1 diabetes. Katzung's Basic and Clinical Pharmacology, 16th Edition, p. 1195.

Type 2 diabetes

Lifestyle and self-management support
- Nutrition plan tailored to the individual
- Regular physical activity
- Weight loss when appropriate
- Sleep, smoking cessation, and blood-pressure/lipid management
- Glucose monitoring when useful, especially for insulin users
Metformin
- Often used as initial medication if kidney function permits.
- Low cost, effective glucose lowering, and low hypoglycemia risk.
- May cause gastrointestinal symptoms and long-term vitamin B12 deficiency in some people.
GLP-1 receptor agonists or dual GIP/GLP-1 agonists
- Examples include semaglutide, dulaglutide, tirzepatide.
- Lower glucose and often produce substantial weight loss.
- Particularly useful when obesity or atherosclerotic cardiovascular disease is present.
- Common adverse effects are nausea, vomiting, and diarrhea.
SGLT2 inhibitors
- Examples include empagliflozin, dapagliflozin.
- Lower glucose and can reduce heart-failure and kidney-disease progression risk in appropriate patients.
- Risks include genital fungal infections, volume depletion, and rarely ketoacidosis, sometimes with only modestly elevated glucose.
Other glucose-lowering options
- DPP-4 inhibitors: modest effect, generally low hypoglycemia risk.
- Sulfonylureas: inexpensive and effective, but can cause hypoglycemia and weight gain.
- Thiazolidinediones: improve insulin sensitivity but may cause weight gain, edema, and can worsen heart failure.
- Insulin: used when glucose is markedly elevated, symptoms of catabolism are present, during acute illness, pregnancy in many cases, or when non-insulin therapy is insufficient.

For type 2 diabetes, medication selection should not be based on HbA1c alone. In people with chronic kidney disease, heart failure, or established cardiovascular disease, drugs with proven organ benefit, especially SGLT2 inhibitors and/or GLP-1 receptor agonists, are often prioritized. This aligns with the 2026 ADA Standards.

Monitoring and goals

HbA1c is often checked about every 3 months when treatment is changing or goals are not met, and at least twice yearly when stable.
A common HbA1c goal for many nonpregnant adults is <7%, but it should be individualized.
Regular surveillance includes blood pressure, cholesterol, kidney function and urine albumin, eye examination, and foot/neuropathy assessment.

When urgent care is needed

Seek urgent medical assessment for vomiting, abdominal pain, rapid or deep breathing, confusion, marked drowsiness, dehydration, or high glucose with ketones. These may indicate diabetic ketoacidosis or hyperosmolar hyperglycemic state. Also treat suspected severe hypoglycemia immediately and seek emergency help if the person is unconscious, having a seizure, or unable to swallow.

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