Type 1vsType 2

If a blood test has shown high sugar, the number alone cannot show which type of diabetes it points to. An A1C of 8% looks the same in type 1 and in type 2. The difference is whether your pancreas can still make insulin. That decides the treatment, and the answer often disagrees with the guess people make from age or weight.

A new high A1C or glucose result needs a visit with your doctor to confirm it, usually with a repeat test, and to find the type. A child or teen with new thirst, frequent peeing or weight loss should be seen the same day, and anyone with high sugar plus vomiting, fast breathing or confusion needs the ER now (see the warning below).

Side by side: how type 1 and type 2 differ

Type 1 makes up 5-10% of diabetes and comes from autoimmune destruction of the beta cells. Type 2 makes up 90-95% and happens when the pancreas still makes insulin, but not enough for a body that has become resistant to it ³. The diabetes page covers early signs across all types, and the type 2 diabetes page covers A1C targets and tracking.

What's going on in the body

After a meal, glucose (sugar) enters the blood. Beta cells in the pancreas release insulin, the hormone that lets muscle, liver and fat cells take that glucose in. Diabetes means this system has failed and blood glucose stays high. Type 1 and type 2 break it at different points; blood sugar explained walks through the system itself.

Type 1 runs silently for months to years before anyone notices. The ADA describes it in three stages ³:

Type 2 starts with insulin resistance: muscle, liver and fat respond less to insulin, so the pancreas makes more to keep glucose normal. When the beta cells can no longer keep up, glucose rises into prediabetes and then diabetes, and their output keeps falling slowly after diagnosis (a HOMA-B estimate tracks this decline). That is why some people with type 2 eventually need insulin, even though their immune system never attacked the pancreas.

Symptoms: the same signs at a different speed

High blood sugar causes the same symptoms in both types: peeing more often, constant thirst, tiredness, blurred vision, slow-healing cuts and repeated infections. In type 1, these usually build over days or weeks, often with unexplained weight loss; in toddlers, the clue can be very heavy diapers or new bedwetting. Because the signs are easy to miss, about 2 in 5 US children and teens (40.3% in 2016) were already in ketoacidosis when type 1 was diagnosed ⁴. In type 2, the same symptoms creep in over years or never appear, and many people learn they have it from a routine blood test.

Who gets which: age, weight and genes

The old labels 'juvenile' and 'adult-onset' diabetes no longer hold. In UK Biobank, 42% of type 1 cases that began before age 60 were diagnosed between 31 and 60, and many of those adults were not started on insulin straight away, as if they had type 2 ². Type 2 is rising in young people too: among US youth, its prevalence rose about 95% from 2001 to 2017, against about 45% for type 1 ⁵.

The traditional paradigms of type 2 diabetes occurring only in adults and type 1 diabetes only in children are no longer accurate, as both diseases occur in both age groups.American Diabetes Association, Standards of Care in Diabetes 2025, Section 2 ³

Weight is also an unreliable guide. People with obesity can develop type 1, and lean people develop type 2, especially people of South and East Asian descent, who tend to develop type 2 at a lower body weight. Family history matters for both, but type 2 has the stronger family link ³, while most people newly diagnosed with type 1 have no close relative with it.

How doctors tell type 1 and type 2 apart on a blood test

Diagnosis uses identical numbers for both types: an A1C of 6.5% or higher, a fasting glucose of 126 mg/dL (7.0 mmol/L) or higher, a 2-hour glucose tolerance result of 200 mg/dL (11.1 mmol/L) or higher, or a random glucose of 200 mg/dL or higher with classic symptoms ³. A diagnosis normally needs two abnormal results unless symptoms make the picture clear. The A1C vs fasting glucose page explains why the two tests sometimes disagree.

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Two other tests identify the type. Islet autoantibodies are antibodies against parts of the beta cell (GAD65, IA-2, ZnT8 and insulin itself), and a positive result points to autoimmune diabetes ³. C-peptide is released in equal amounts with every unit of insulin the pancreas makes, so it measures your own insulin output even if you inject insulin. The ADA/EASD consensus sets adult cut-offs: below 200 pmol/L (about 0.6 ng/mL) points to type 1, above 600 pmol/L (about 1.8 ng/mL) points to type 2, and the test is most reliable more than 3 years after diagnosis ¹.

When it doesn't fit either type: LADA, MODY and misdiagnosis

LADA (latent autoimmune diabetes in adults, sometimes called type 1.5) is autoimmune diabetes that starts in adulthood and progresses slowly. People with LADA test positive for islet antibodies but manage without insulin for at least the first 6 months, so many are labeled type 2 at first ⁶. MODY (maturity-onset diabetes of the young) is a rare form, about 1-2% of diabetes, caused by a change in a single gene and passed down through families. A UK study estimated that more than 80% of MODY cases had not been correctly diagnosed and were treated as type 1 or type 2 ⁷; some forms respond to tablets better than to insulin. Diabetes can also follow pancreatitis or steroid treatment, or appear first in pregnancy (gestational diabetes).

Treatment: insulin from day one vs a stepped plan

Type 1 treatment replaces the missing hormone. Most people use background (basal) insulin plus mealtime doses, given by pen or pump, and many wear a continuous glucose monitor (CGM), a skin sensor that reads glucose every few minutes. Someone with type 1 cannot go without insulin, even on a sick day with no appetite; missing insulin can bring on DKA within hours.

Type 2 treatment usually starts with changes to eating, activity and weight, with metformin as the usual first tablet. Doctors may add GLP-1 receptor agonists (injections such as semaglutide that lower appetite and glucose) or SGLT2 inhibitors (tablets such as empagliflozin that pass extra sugar out in the urine), particularly for people with heart or kidney disease, and some people go on to need insulin as their own output falls. Low blood sugar (hypoglycemia) is a common risk with insulin and with older tablets called sulfonylureas, and is rare with metformin alone. Shakiness, sweating, confusion or unusual behavior can mean low blood sugar; fainting, a seizure or being unable to swallow is an emergency: call 911.

The usual first prescription for type 2

First-line for type 2MetforminA prescription medicine that lowers glucose production by the liver; the usual first tablet for type 2

Berberine is sold as a natural alternative to metformin; the berberine vs metformin page weighs the evidence for that claim.

Can either type be prevented or reversed?

Nothing prevents type 1 today, but onset can be delayed. In relatives at high risk who were already at stage 2, a single 14-day course of teplizumab delayed clinical type 1 to a median of 48.4 months, against 24.4 months on placebo ⁸. It is now approved in the US for people aged 8 and older with stage 2 type 1 ³. Antibody screening of relatives is how people at stage 1 or stage 2 get found.

The risk of type 2 can be cut sharply. In the Diabetes Prevention Program, people with prediabetes who followed an intensive lifestyle program developed type 2 at a 58% lower rate than the placebo group over about 3 years, and metformin lowered the rate by 31% ⁹. For people who already have type 2, the DiRECT trial put 46% into remission at 12 months with a medically supervised program: a low-calorie meal-replacement diet followed by food reintroduction, with diabetes medicines stopped by the care team at the start. Remission rose with the amount of weight lost ¹⁰.

Doctors now define remission of type 2 as an A1C below 6.5% at least 3 months after glucose-lowering medicine has been stopped ¹¹; DiRECT used a 2-month window. Any change to diabetes medicine, including stopping it, should be planned with your doctor, because cutting calories hard while still on insulin or some tablets can drop blood sugar too low. Remission does not apply to type 1 or LADA, where insulin must never be stopped. Diabetes can come back, especially if weight returns, so people in remission still need yearly A1C checks.

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