Prediabetes, Insulin Resistance and Type 2 Diabetes: Drawing the Distinctions
Level 2, Intermediate
In brief
Insulin resistance is a physiological state; prediabetes and type 2 diabetes are diagnoses defined by glucose thresholds. Prediabetes is defined by impaired fasting glucose, impaired glucose tolerance or an HbA1c in an intermediate range, with thresholds that differ between organisations. Many people with insulin resistance have normal glucose for years. HbA1c can be misleading in anaemia, haemoglobin variants, kidney disease and pregnancy, and not every adult with diabetes has type 2.
The terms insulin resistance, prediabetes and type 2 diabetes are often used as if they described a single slope of increasing severity. They are related, but they are not the same kind of thing. Insulin resistance is a physiological state, measured imperfectly and without a universal diagnostic threshold. Prediabetes and type 2 diabetes are diagnoses defined by specific glucose based criteria that differ between organisations. Understanding these distinctions allows practitioners to communicate accurately with patients and colleagues, stage metabolic risk sensibly and avoid both missed diagnoses and unnecessary labels.
Insulin resistance: a state, not a diagnosis
Insulin resistance describes reduced sensitivity of tissues to insulin, compensated for by increased insulin secretion. It develops gradually, often over a decade or more before glucose rises, and is identified from clinical features and laboratory patterns rather than a single test. There is no internationally agreed threshold for diagnosing it in routine practice, and it does not usually appear as a formal diagnosis in clinical records. It is best thought of as an underlying mechanism that increases the risk of several conditions, including prediabetes, type 2 diabetes, fatty liver disease, polycystic ovary syndrome and cardiovascular disease.
Diagnostic criteria for prediabetes and diabetes
| Test | Prediabetes, American Diabetes Association | Common alternative thresholds | Diabetes |
|---|---|---|---|
| Fasting plasma glucose | 5.6 to 6.9 mmol/L (100 to 125 mg/dL), impaired fasting glucose | The World Health Organization defines impaired fasting glucose from 6.1 mmol/L (110 mg/dL) | 7.0 mmol/L (126 mg/dL) or above |
| 2 hour glucose on oral glucose tolerance test | 7.8 to 11.0 mmol/L (140 to 199 mg/dL), impaired glucose tolerance | Similar across organisations | 11.1 mmol/L (200 mg/dL) or above |
| HbA1c | 39 to 47 mmol/mol (5.7 to 6.4 percent) | Some bodies, including in the United Kingdom, use 42 to 47 mmol/mol (6.0 to 6.4 percent) | 48 mmol/mol (6.5 percent) or above |
| Random glucose | Not used for prediabetes | 11.1 mmol/L (200 mg/dL) or above with classic symptoms |
In the absence of unequivocal hyperglycaemia or symptoms, a diabetes diagnosis generally requires confirmation with a repeat test or 2 different abnormal tests. The different thresholds for prediabetes mean that the same person may be classified differently depending on the country and the test used. The 3 tests also identify partly different groups of people: impaired fasting glucose, impaired glucose tolerance and raised HbA1c overlap only partially.
What prediabetes means for risk
Prediabetes carries an increased risk of progressing to type 2 diabetes, with estimates of annual progression commonly in the range of 5 to 10 percent, varying with the definition and population. Risk is highest when both fasting glucose and glucose tolerance are abnormal, and when HbA1c is towards the upper end of the range. Prediabetes is also associated with increased cardiovascular risk. Importantly, many people with prediabetes do not progress, and some return to normal glucose regulation, particularly with weight loss and increased activity. Structured lifestyle programmes have been shown to reduce progression substantially.
When HbA1c can mislead
HbA1c reflects average glucose over about 2 to 3 months because it measures glucose attached to haemoglobin. Anything that changes red cell lifespan or haemoglobin structure can distort it.
- Falsely low: recent blood loss or transfusion, haemolytic anaemia, treatment of iron or B12 deficiency with rapid red cell turnover, some haemoglobin variants, pregnancy, advanced kidney disease with erythropoietin treatment.
- Falsely high: iron deficiency anaemia, some haemoglobin variants, severe kidney disease in some cases.
- Other considerations: ethnic differences in HbA1c at similar glucose levels have been reported, and HbA1c is not recommended for diagnosing diabetes in pregnancy, children in some guidelines, or suspected type 1 diabetes, where glucose measurements are preferred.
When HbA1c and glucose measurements disagree, or when these conditions are present, glucose based tests are more reliable.
Not every adult with diabetes has type 2
Type 2 diabetes is by far the most common form in adults, but other forms are important to recognise because they are treated differently.
| Type | Clues |
|---|---|
| Type 1 diabetes in adults, including slowly progressive autoimmune forms | Lean body habitus, rapid progression, weight loss, ketones, personal or family history of autoimmunity; islet antibodies confirm |
| Monogenic diabetes | Onset at a young age with a strong family history across generations, often without obesity |
| Diabetes secondary to pancreatic disease | Previous pancreatitis, pancreatic surgery, cystic fibrosis or pancreatic cancer; often with exocrine insufficiency |
| Medication related diabetes | Glucocorticoids, some antipsychotics and other medicines |
| Gestational diabetes | Diagnosed in pregnancy; indicates increased lifetime risk of type 2 diabetes |
Misclassifying autoimmune diabetes as type 2 can lead to delayed insulin treatment and diabetic ketoacidosis. A practitioner who notices that a person’s diabetes does not behave like typical type 2 disease should raise this with their doctor.
Remission of type 2 diabetes
An international consensus has defined remission of type 2 diabetes as an HbA1c below 48 mmol/mol (6.5 percent) measured at least 3 months after stopping glucose lowering medicines. Remission is most often achieved through substantial weight loss, through structured dietary programmes or bariatric surgery. It is not a cure: continued monitoring is needed because glucose can rise again, and complications may still develop. Using the term carefully avoids giving patients the impression that the condition has disappeared permanently.
A practical staging approach
| Stage | Typical findings | Priorities |
|---|---|---|
| Insulin resistance with normal glucose | Central adiposity, family history, high triglycerides, low HDL, rising glucose trends within normal range | Lifestyle intervention; monitoring of trajectory |
| Prediabetes | Glucose or HbA1c in the intermediate range | Structured lifestyle programme; cardiovascular risk assessment; regular review |
| Type 2 diabetes | Diagnostic thresholds met and confirmed | Comprehensive diabetes care, including medication where indicated, complication screening and lifestyle intervention |
| Remission | HbA1c below 48 mmol/mol off medication for at least 3 months | Continued monitoring and support |
An illustrative case
A 38 year old woman with a BMI of 22 has an HbA1c of 50 mmol/mol found on routine testing. She has lost weight unintentionally over the past year, and her mother has hypothyroidism. She has been told she has type 2 diabetes and advised to lose weight. The practitioner notices that her presentation is unusual for type 2 diabetes and raises this with her doctor, who tests for islet antibodies. They are positive, indicating autoimmune diabetes. Her treatment plan changes accordingly, and she is monitored for progression to insulin dependence. The functional approach to her nutrition and lifestyle still applies, but it now sits within the right diagnosis.
Precise language, better care
Insulin resistance, prediabetes and type 2 diabetes are connected, but precision about each matters. Using the right criteria, recognising when tests mislead, noticing when diabetes is not typical type 2 and describing remission accurately all make metabolic care safer and more effective.
Common questions
Is insulin resistance the same as prediabetes?
What HbA1c indicates prediabetes?
Can type 2 diabetes go into remission?
References and guidelines
- American Diabetes Association Professional Practice Committee. Diagnosis and classification of diabetes: Standards of Care in Diabetes. Diabetes Care. Published annually.
- World Health Organization. Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia. Geneva: WHO; 2006.
- Riddle MC, Cefalu WT, Evans PH, et al. Consensus report: definition and interpretation of remission in type 2 diabetes. Diabetes Care. 2021;44(10).
- Tabák AG, Herder C, Rathmann W, et al. Prediabetes: a high risk state for diabetes development. The Lancet. 2012;379(9833).
- Knowler WC, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. New England Journal of Medicine. 2002;346(6).
- Holt RIG, DeVries JH, et al. The management of type 1 diabetes in adults: a consensus report by the ADA and EASD. Diabetes Care. 2021;44(11).
Continue your learning
Staging metabolic risk precisely
Distinguishing diabetes, prediabetes and insulin resistance accurately is a core objective of the Blood Sugar Dysfunction module in IIFM’s 6 month Functional Medicine and Clinical Nutrition program.
This article is for the education of healthcare professionals. It is not a substitute for individual medical advice, diagnosis or treatment, and does not change any practitioner’s scope of practice. Regulation and guidelines differ between countries.