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Conditions

Diabetes mellitus

A chronic disorder of glucose metabolism: type 2 is linked to insulin resistance and sharply raises cardiovascular risk.

Diabetes mellitus — blood glucose level and a glucometer

Diabetes mellitus is a chronic metabolic disorder in which glucose in the blood is persistently elevated: the body either lacks insulin, or the cells stop responding to it (insulin resistance).

Chronically high blood sugar damages the vessels, nerves, kidneys and eyes over the years. That is why diabetes is diagnosed and monitored by specific laboratory thresholds, not by how a person feels.

The main types

Type 1 — autoimmune destruction of the pancreatic beta cells, an absolute insulin deficiency (more often in the young).

Type 2 — the most common (more than 90%): insulin resistance plus a relative lack of insulin (see type 2 diabetes).

Gestational — first detected during pregnancy (GDM). A pre-stage is distinguished separately — prediabetes.

Symptoms and complications

The classic signs are thirst, frequent urination, weight loss, fatigue, poor wound healing. But type 2 often runs latent for years.

Without control, high blood sugar leads to damage of the vessels and heart, kidneys (nephropathy), nerves (neuropathy) and the retina of the eye (retinopathy).

Can it be prevented

Type 2 diabetes is largely preventable and at early stages partly reversible: weight loss, a diet with a restriction of fast carbohydrates and regular activity. The prediabetes stage can be returned to normal.

Reference ranges

The diagnosis is made by any one of the criteria (ADA, 2026); in the absence of overt hyperglycemia — with confirmation by a repeat test:

Fasting glucose≥ 7.0 mmol/L (126 mg/dL)
Glucose at 2 h (glucose tolerance test)≥ 11.1 mmol/L (200 mg/dL)
Glycated hemoglobin (HbA1c)≥ 6.5%
Random glucose + symptoms≥ 11.1 mmol/L
Important: Prediabetes: fasting glucose 5.6–6.9; HbA1c 5.7–6.4%; at 2 h 7.8–11.0 mmol/L. A single borderline result is a reason to retest, not a diagnosis.

Calculate using this marker

Calculators where Diabetes mellitus is used directly:

Diabetes Risk Screening for hidden prediabetes and type 2 diabetes from labs and risk factors Open Metabolic Syndrome IDF/NCEP criteria — waist circumference, blood pressure, glucose, and lipids Open

Frequently asked questions

What blood sugar counts as diabetes?

Fasting glucose 7.0 mmol/L or higher, or 2 hours after a glucose load 11.1 or higher, or HbA1c 6.5% or higher. Values between normal and these thresholds are prediabetes; that is not yet diabetes, but a reason to act.

Can diabetes be cured?

Type 1 diabetes is incurable and requires insulin for life. Type 2 diabetes at early stages can be brought into sustained remission through weight loss and lifestyle, but the predisposition remains and constant control is needed.

Related terms

Type 2 diabetes mellitus Persistently high sugar due to insulin resistance and a relative lack of insulin Prediabetes Sugar above normal but not yet diabetes — a reversible "yellow zone" Insulin resistance Reduced sensitivity of cells to insulin Fasting glucose Fasting blood sugar — the main marker of carbohydrate metabolism Glycated hemoglobin HbA1c — an indicator of blood sugar over 3 months Metabolic syndrome A cluster of cardiometabolic risk factors Gestational diabetes Diabetes first detected during pregnancy Impaired glucose tolerance (IGT) An intermediate state between normal and diabetes

Sources

  1. ADA. Standards of Care in Diabetes — 2026: Diagnosis and Classification
  2. American Diabetes Association — Diagnosis
  3. MedlinePlus (NIH) — Diabetes
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This content is educational and does not replace consultation with a physician. Reference ranges may vary depending on the laboratory and method — rely on the ranges stated on your own test report.
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