What is type 2 diabetes?
Type 2 diabetes is a long-term condition in which blood sugar (glucose) stays too high. The body stops responding properly to insulin, the hormone that moves glucose into cells. This is called insulin resistance, and over time the pancreas cannot keep up.
Type 1 diabetes is different: an autoimmune disease that usually starts younger and stops insulin production. Type 2 is far more common, and it often develops over years with no symptoms.
Why catching it early matters
High blood sugar slowly harms the small blood vessels of the eyes, kidneys and nerves. It also speeds up disease in the heart and large arteries. Most people first pass through prediabetes, a stage of mildly raised glucose that a blood test can find.
How blood tests detect it
Diabetes is diagnosed with blood tests, not symptoms. A comprehensive blood panel can measure fasting glucose and HbA1c, which reflects average blood sugar over about three months. NIDDK uses these ranges:
A ladder like this is the general pattern, not a rule your case must obey. Reporting conventions differ between hospitals, and two experienced clinicians can read the same finding and reasonably advise differently. Where your report or your doctor differs from this table, go with them — they are looking at your actual result.
One abnormal value is not a diagnosis on its own. Without clear symptoms of very high blood sugar, the ADA requires two abnormal results: two different tests, or the same test repeated. HbA1c can also mislead in some people, such as those with anemia or certain hemoglobin variants.
Who should be tested
| Body | Who to test |
|---|---|
| USPSTF (US, 2021) | Adults 35–70 with overweight or obesity |
| ADA (US, 2026) | Everyone from 35; at any age with overweight plus a risk factor; repeat at least every 3 years if normal |
The ADA lists risk factors including:
- A parent, sibling or child with diabetes
- High blood pressure, or low HDL and high triglycerides
- Physical inactivity, or polycystic ovary syndrome
- Diabetes during a past pregnancy, which calls for testing every 1–3 years
For people of Asian ancestry, the ADA sets the overweight threshold lower, at a BMI of 23 rather than 25. Diabetes tends to appear at a lower body weight.
Lowering the risk, and what to do now
Modest weight loss, regular activity and a better diet lower the chance that prediabetes becomes diabetes. Once diabetes is established it is usually managed rather than cured. Some people reach normal blood sugar without medication, but it can return, so monitoring continues.
- Vomiting, deep fast breathing, fruity breath, confusion or drowsiness, especially with known diabetes: In Taiwan call 119 (the local equivalent of 911).
- Constant thirst, frequent urination, blurred vision or unexplained weight loss: see a doctor soon.
- No symptoms: check yourself against the table above, and ask for a repeat test if one result comes back abnormal.
