The key player is insulin, a hormone made by your pancreas. Insulin signals your cells to take glucose in from the bloodstream and use it for energy. When your body either doesn't make enough insulin, or your cells stop responding to it well, glucose stays in the blood instead of being used — and levels rise.

There isn't just one kind of diabetes. Here are the main ones.

Type 1

Type 1 diabetes is an autoimmune condition: the immune system mistakenly attacks the cells in the pancreas (the beta cells) that make insulin. With those cells gone, the body can no longer produce the insulin it needs — so blood glucose rises.

It's most often diagnosed in children and young adults, and people with type 1 take insulin every day to do the job their pancreas no longer can.

Type 2

Type 2 is the most common form. Here, the issue is usually that the cells have become less responsive to insulin's signal — and/or the pancreas isn't releasing quite enough. The pancreas is still working, but it can't keep blood sugar in a healthy range on its own.

Type 2 can develop at any age, even in childhood, though it's most common in middle-aged and older adults.

Gestational diabetes

Gestational diabetes appears during pregnancy, usually in the second or third trimester. Pregnancy hormones can make it harder for the body to use insulin properly, and pregnancy itself places heavy demands on the body. Some people simply can't produce enough extra insulin to keep up — and blood sugar rises.

The reassuring part: it usually goes away after the baby arrives. It does, however, raise the chance of developing diabetes later in life, so it's worth keeping an eye on.

The rarer forms

A small share of cases — only a few percent — fall outside these three. These include various forms of monogenic diabetes (caused by a single gene change), diabetes linked to cystic fibrosis, and diabetes triggered by certain medications (such as some steroids and antipsychotics), surgery, or hormonal imbalances.

How diabetes is diagnosed

Diagnosis usually rests on a blood test, and there are a few common ones:

• Fasting plasma glucose (FPG) — blood drawn after at least 8 hours without food, typically first thing in the morning.

• Oral glucose tolerance test (OGTT) — blood drawn after the same overnight fast, then again two hours after you drink a glucose drink.

• Random plasma glucose — checked at any time, regardless of when you last ate. Together with your symptoms, it can diagnose diabetes (but not prediabetes).

  
  

A positive result is normally confirmed by repeating the same test on another day. The World Health Organization's thresholds for diabetes are:

• a random plasma glucose of 11.1 mmol/l or above, or

• a fasting plasma glucose of 7.0 mmol/l or above (whole blood: 6.1 or above), or

• a 2-hour plasma glucose of 11.1 mmol/l or above after a 75 g glucose drink in an OGTT.

(Numbers can appear as mmol/l or mg/dL depending on where you are.)

Gestational diabetes uses its own WHO thresholds, where just one of these values is enough for a diagnosis:

• fasting plasma glucose 5.1–6.9 mmol/l, or

• 1-hour plasma glucose 10.0 mmol/l or above, or

• 2-hour plasma glucose 8.5–11.0 mmol/l after a 75 g glucose drink.

Your doctor may also check HbA1c, which reflects your average blood sugar over roughly the past 2–3 months — a longer-term picture rather than a single moment.

Prediabetes — a turning point, not a verdict

Sometimes blood sugar is higher than normal but not yet in the diabetes range. That might be called prediabetes, intermediate hyperglycaemia, or being at higher risk of developing diabetes. (When it shows up as raised fasting glucose it's called impaired fasting glucose, IFG; when it shows up during the OGTT, impaired glucose tolerance, IGT.)

It's best thought of as an early, helpful heads-up rather than a diagnosis to fear. At this stage it's often very possible to turn things around and avoid type 2 diabetes — far more so than once the condition has progressed. Small, steady changes really can make a difference, and you don't have to do it alone.

General information — not medical advice. Speak with your doctor about your own health.