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Medical illustration showing insulin and glucose interacting with cell receptors to represent insulin resistance

Insulin Resistance: What It Is, Causes and How It Is Tested


Metabolic health guide

Insulin resistance happens when the body's cells do not respond to insulin as effectively as they should. The pancreas may compensate by producing more insulin to help keep blood glucose controlled.

Insulin resistance can develop before blood glucose becomes persistently raised and may cause no obvious symptoms. Over time, reduced insulin sensitivity can be associated with a higher risk of developing type 2 diabetes.

Fasting insulin, glucose, HbA1c and calculations such as HOMA-IR can provide useful information about glucose and insulin metabolism, but no single result should be used as a stand-alone diagnosis.


Reduced insulin sensitivity Cells respond less effectively to insulin.

Often symptom-free Insulin resistance can develop before obvious symptoms appear.

Results need context Fasting insulin and HOMA-IR are not stand-alone diagnoses.

What is insulin resistance?

Insulin resistance means that tissues including muscle, body fat and the liver have a reduced response to insulin. Insulin is a hormone produced by the pancreas that plays an important role in regulating the amount of glucose circulating in the blood.

When insulin sensitivity decreases, the body may compensate by producing more insulin. This additional insulin can help keep blood glucose within an appropriate range, particularly during the earlier stages.

This means someone may have increased insulin production before standard glucose measurements become clearly abnormal.

How does insulin normally work?

After you eat food containing carbohydrate, some of it is broken down into glucose. Glucose enters the bloodstream and can then be used by cells as a source of energy.

As blood glucose rises, the pancreas releases insulin. Insulin helps glucose move from the bloodstream into cells and also affects how the liver stores and releases glucose.

With insulin resistance, cells respond less effectively to that signal. The pancreas may therefore release more insulin to compensate. If this compensation eventually becomes insufficient, blood glucose can rise.

What can increase the risk of insulin resistance?

Insulin resistance rarely has one single cause. Genetics, body composition, physical activity, medical conditions and other factors can all affect insulin sensitivity.

Factors associated with an increased risk of type 2 diabetes and reduced insulin sensitivity can include:

  • excess body fat, particularly around the abdomen;
  • low levels of physical activity;
  • a family history of type 2 diabetes;
  • high blood pressure and other cardiometabolic risk factors;
  • polycystic ovary syndrome (PCOS);
  • a history of gestational diabetes;
  • certain medicines or medical conditions; and
  • age and ethnic background, which can influence type 2 diabetes risk.

Weight alone cannot determine whether someone has insulin resistance. Risk should be considered alongside medical history, family history, blood pressure, glucose-related blood results and other relevant findings.

NICE provides further information about preventing type 2 diabetes in people at high risk .

Does insulin resistance cause symptoms?

Insulin resistance often does not cause obvious symptoms, particularly during its earlier stages.

Symptoms such as tiredness, weight changes or increased appetite are non-specific and can occur for many different reasons. They should not be used to diagnose insulin resistance.

If blood glucose becomes significantly raised, symptoms associated with diabetes may develop. These can include increased thirst, passing urine more frequently, tiredness and unexplained weight loss.

You can read more in the NHS guide to type 2 diabetes symptoms and diagnosis .

What is the difference between insulin resistance and prediabetes?

Insulin resistance and prediabetes are related, but they do not mean the same thing.

Insulin resistance describes reduced responsiveness to insulin. Prediabetes, also called non-diabetic hyperglycaemia, describes blood glucose levels that are higher than normal but not high enough for a diagnosis of diabetes.

Insulin resistance can develop before glucose or HbA1c reaches a range associated with prediabetes. If insulin resistance progresses and pancreatic compensation becomes insufficient, blood glucose may increase.

This does not mean everyone with insulin resistance will develop type 2 diabetes. Individual risk varies.

How is insulin resistance assessed?

There is no single routine blood result that gives a complete assessment of insulin resistance in every person. Different biomarkers provide different information and should be interpreted alongside the wider clinical picture.

Glucose

Glucose testing measures the amount of glucose in the blood at the time the sample is taken. A fasting measurement provides information about fasting blood glucose regulation.

Insulin

Insulin testing measures the hormone involved in regulating blood glucose. A fasting insulin result can provide information about insulin production in the fasting state.

HbA1c

HbA1c estimates average blood glucose over approximately the previous two to three months. It is used within established diabetes assessment and monitoring pathways.

C-peptide

C-peptide is released when the pancreas produces insulin. It can provide additional information about the body's own insulin production in appropriate clinical circumstances.

Marker What it can show Important limitation
Fasting glucose Blood glucose at a particular fasting time point. It does not directly measure insulin sensitivity.
Fasting insulin Insulin concentration while fasting. Results vary between individuals and laboratory methods.
HbA1c Average glucose exposure over recent months. It does not directly measure insulin resistance.
C-peptide Information about the body's own insulin production. It requires clinical context and does not diagnose insulin resistance by itself.
HOMA-IR A calculated estimate using fasting glucose and fasting insulin. There is no single universal diagnostic cut-off suitable for every population or laboratory method.

Reference ranges and interpretation can vary according to laboratory method, units, fasting conditions and individual circumstances.

What is HOMA-IR?

HOMA-IR stands for Homeostatic Model Assessment of Insulin Resistance. It is a calculated index based on fasting glucose and fasting insulin measurements.

The calculation can provide additional information about the relationship between glucose and insulin in the fasting state. However, HOMA-IR is method-dependent and is not universally standardised as a routine diagnostic test.

There is therefore no single HOMA-IR number that should automatically be treated as proof that a person does or does not have insulin resistance.

Can you have normal blood glucose and still have reduced insulin sensitivity?

Yes. It is possible for blood glucose to remain within the expected range during earlier stages of reduced insulin sensitivity.

The pancreas may initially compensate by producing more insulin. This can help maintain glucose levels despite a weaker response to insulin in the body's tissues.

This is one reason fasting insulin and glucose considered together can provide different information from glucose alone. However, a raised fasting insulin result does not automatically prove insulin resistance, and a normal result cannot exclude every metabolic problem.

Does insulin resistance mean you have diabetes?

No. Insulin resistance does not automatically mean that someone has diabetes.

Insulin resistance is involved in the development of many cases of type 2 diabetes, but diabetes is assessed using recognised glucose-based criteria rather than fasting insulin or HOMA-IR alone.

If you are primarily interested in glucose-related biomarkers, you can also review the AIS Health Check Diabetes Blood Test Panel .

Can insulin sensitivity improve?

Insulin sensitivity can change over time. Regular physical activity and, where appropriate, reducing excess body weight can improve glucose regulation and reduce the risk of developing type 2 diabetes.

Dietary patterns, sleep, smoking, alcohol intake and management of other cardiovascular and metabolic risk factors can also be relevant.

Eligible people in England may be referred to the Healthier You NHS Diabetes Prevention Programme .

There is no single lifestyle approach suitable for everyone. People who already have diabetes, are pregnant, have significant medical conditions or take medicines affecting blood glucose may need personalised medical advice.

Prescribed medicines should not be stopped or changed because of an insulin or HOMA-IR result unless a healthcare professional has advised you to do so.


Want to assess insulin and glucose markers together?

The current AIS Health Check Insulin Resistance Test combines glucose, HbA1c, insulin, C-peptide and HOMA-IR with selected health measurements.

Because fasting insulin and glucose are used in the assessment, the current preparation instructions advise having the blood test in the morning following an overnight fast, with no food or drinks other than water for 8–12 hours beforehand.

Continue prescribed medicines as usual unless a healthcare professional has specifically advised otherwise.

How should insulin resistance test results be interpreted?

Insulin-resistance-related blood results are generally most useful when considered as a pattern rather than as isolated numbers.

Fasting insulin can be considered alongside fasting glucose and HOMA-IR. HbA1c adds information about average glucose exposure over a longer period, while C-peptide can provide additional information about insulin production.

Results may also be influenced by fasting duration, medicines, recent illness, physical activity, biological variation and the laboratory method used.

An abnormal result does not automatically establish a diagnosis. Repeat testing or further medical assessment may sometimes be appropriate. Equally, normal results cannot exclude every cause of symptoms or every future metabolic risk.

AIS customers can also read the AIS Health Check guide to understanding results .

Frequently asked questions about insulin resistance

Can insulin resistance occur without symptoms?

Yes. Reduced insulin sensitivity can develop without obvious symptoms, particularly before blood glucose becomes significantly raised. Symptoms alone cannot confirm or exclude insulin resistance.

Is HOMA-IR a diagnostic test for diabetes?

No. HOMA-IR is a calculated estimate based on fasting insulin and glucose. Diabetes diagnosis relies on recognised glucose-based testing pathways rather than HOMA-IR alone.

Does a high fasting insulin result mean I have insulin resistance?

Not necessarily. Insulin values vary between individuals and laboratory methods. A fasting insulin result should be interpreted alongside glucose, HbA1c, fasting conditions, medical history and other relevant findings.

Do I need to fast for the AIS Insulin Resistance Test?

The current AIS Health Check preparation instructions advise testing in the morning following an overnight fast, with no food or drinks other than water for 8–12 hours before the blood test.

What should I do if my results are abnormal?

The appropriate next step depends on which markers are abnormal and your wider circumstances. A healthcare professional may consider your medical history, previous results, medicines, blood pressure, cholesterol and other metabolic risk factors. Repeat testing or additional assessment may sometimes be appropriate.


Check your insulin and glucose markers

If you want to measure fasting insulin and glucose alongside HbA1c, C-peptide and HOMA-IR, review the current AIS Health Check test details and preparation requirements before booking.

Sources and further reading

This article provides general health information and is not a substitute for individual medical advice, diagnosis or treatment.