Biomarker Glossary

Insulin

Insulin is the hormone that moves glucose from your bloodstream into your cells. A fasting insulin blood test is one of the best early markers of insulin resistance, the underlying driver of type 2 diabetes, PCOS and metabolic syndrome, often years before HbA1c or fasting glucose become abnormal.

Also known as: Serum Insulin, Fasting Insulin

Insulin is most informative when read alongside related markers like Glucose and HbA1c. A single number rarely tells the whole story. If your reading sits outside the typical range, share the full report with your GP or healthcare professional before drawing conclusions.

What is Insulin?

Insulin is made by the beta cells of the pancreas. After you eat, blood glucose rises and the pancreas releases insulin to move glucose into muscle, liver and fat cells for energy or storage.

If cells become resistant to insulin, the pancreas compensates by producing more. Fasting insulin rises long before fasting glucose or HbA1c moves out of normal range, making it one of the earliest detectable markers of metabolic dysfunction.

Fasting insulin is often combined with fasting glucose to calculate HOMA-IR, a research grade measure of insulin resistance.

Why test Insulin?

  • To detect insulin resistance early, often before HbA1c or fasting glucose has changed.
  • If you have central weight gain, fatigue after meals, sugar cravings or difficulty losing weight.
  • To investigate suspected PCOS, fatty liver or metabolic syndrome.
  • To monitor metabolic health during weight loss, GLP-1 medication, or biohacking interventions.
To detect insulin resistance early, often before HbA1c or fasting glucose has changed.

Insulin normal range (UK)

Result What it means
Below 5 mIU/L (fasting) Optimal insulin sensitivity
5 to 10 mIU/L Average. Mild insulin resistance may be developing
10 to 25 mIU/L Insulin resistance
Above 25 mIU/L Marked insulin resistance, often with PCOS or type 2 diabetes

Standard NHS laboratories report a wide reference range up to about 25 mIU/L as "normal", but functional medicine and metabolic researchers consider levels above 5 mIU/L as the start of insulin resistance, particularly in lean adults.

About these ranges. The ranges above are typical UK clinical lab ranges aligned to NHS and Royal College of Pathologists guidance. Your Chxhealth report will show the specific reference range used by our partner lab, Randox, for each marker. Lab ranges vary slightly between providers and assays. Always interpret your results in the context of the range printed on your own report.

What causes high Insulin?

  • Insulin resistance from a diet high in refined carbohydrates and sugar
  • Central obesity and lack of activity
  • Polycystic ovary syndrome (PCOS)
  • Type 2 diabetes (early or pre diabetic stages)
  • Cushing's syndrome (chronic high cortisol)
  • Some medications such as steroids and antipsychotics
  • Insulin producing tumour (insulinoma, very rare)

What causes low Insulin?

  • Type 1 diabetes (autoimmune destruction of insulin producing cells)
  • Late stage type 2 diabetes (pancreatic burnout)
  • Severe pancreatitis or pancreatic surgery
  • Prolonged fasting

Symptoms of high Insulin

  • Fatigue, particularly after meals
  • Cravings for sweet or starchy foods
  • Difficulty losing weight despite calorie restriction
  • Central (abdominal) weight gain
  • Skin tags, dark velvety patches in skin folds (acanthosis nigricans)
  • Irregular periods or PCOS symptoms in women
  • Erectile dysfunction in men
  • High blood pressure or fatty liver

Symptoms of low Insulin

  • Symptoms typically reflect uncontrolled blood sugar (hyperglycaemia): thirst, frequent urination, weight loss, fatigue.
  • In type 1 diabetes or severe pancreatic failure, low insulin can rapidly lead to diabetic ketoacidosis.

How is Insulin tested?

Insulin is measured from a small blood sample, taken after a 12 hour fast.

Do not eat or drink anything except water before the test. Avoid coffee, which can affect insulin sensitivity.

Chxhealth samples are analysed by Randox, a UK laboratory accredited by UKAS. Results return in 3 to 5 working days.

How to support healthy Insulin levels

  • Reduce sugar and refined carbohydrates. Even short term low carb diets noticeably lower fasting insulin within weeks.
  • Eat protein and fibre with every meal.
  • Strength training is one of the most effective ways to lower insulin. Aim for 2 to 3 sessions per week.
  • Walk after meals. A 10 to 15 minute walk lowers post meal insulin response significantly.
  • Prioritise 7 to 9 hours of sleep. Poor sleep raises insulin resistance within days.
  • Intermittent fasting (16:8 or alternate day) lowers fasting insulin in many people, though it is not for everyone.

These are general lifestyle suggestions. Chxhealth is an information service. For personal medical advice, please speak to a healthcare professional.

Chxhealth panels that test Insulin

16 Chxhealth biomarker panels include Insulin. Each is analysed by Randox, a UK laboratory accredited by UKAS. Reports are delivered in 3 to 5 working days.

Insulin FAQs

What is a healthy fasting insulin level?

Below 5 mIU/L when fasted for 12 hours is considered optimal by metabolic researchers. The standard NHS reference range extends to about 25 mIU/L, but anything above 10 mIU/L usually signals developing insulin resistance.

Can insulin be high while glucose is normal?

Yes. This is the hallmark of early insulin resistance: the pancreas keeps glucose under control by producing more insulin. Glucose only starts rising once insulin production cannot keep up, often years later.

What is HOMA-IR?

HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) is a calculation using fasting insulin and fasting glucose. Values below 1.0 are excellent, 1.0 to 1.9 are average, and above 2.0 suggests insulin resistance.

Can I reverse insulin resistance?

Yes. For most people, sustained changes to diet (less sugar, more protein and fibre), regular exercise (especially strength training), better sleep and weight loss can lower fasting insulin within weeks to months.

Should I test insulin or HbA1c?

Insulin is the earliest marker, often abnormal years before HbA1c. HbA1c is more useful for diagnosing and tracking diabetes once established. Testing both gives the fullest picture of metabolic health.

Often tested with Insulin

The biomarkers below are commonly investigated alongside Insulin because they reveal connected aspects of the same physiological picture:

  • Glucose: HOMA-IR scoring uses both fasting glucose and insulin.
  • HbA1c: HbA1c shows longer-term trend that insulin alone cannot.
  • SHBG: Low SHBG often accompanies high insulin and metabolic dysfunction.
  • Triglycerides: Both rise together in insulin resistance.

Choose the right test for your goal

If you are reading about Insulin because of a specific health goal, our buying guides walk you through which Chxhealth panels fit:

Sources and further reading

This page is informed by guidance from the NHS, NICE, Royal College of Pathologists and other UK authoritative bodies. For deeper detail or to verify the information, see:

About this page. Last reviewed: 13 May 2026. Next scheduled review: May 2027. This page has not yet been independently reviewed by a clinician. It is written from authoritative UK medical guidance (NHS, NICE, Royal College of Pathologists, peer-reviewed sources) but has not undergone formal clinical sign off.

Important. Chxhealth is a UK information service. We do not diagnose, treat or prescribe. The reference ranges and information on this page are general educational content and should not be used as a substitute for advice from a qualified healthcare professional. For any concerns about your health or results, please speak to your GP or another healthcare professional.