Biomarker Glossary

Glucose

Glucose is the main sugar in your blood and your body's primary energy source. A fasting blood glucose test measures your blood sugar after at least 8 hours without food and is one of the standard UK tests for diagnosing diabetes and prediabetes, alongside HbA1c.

Also known as: Blood Sugar, Fasting Glucose, FBG, Plasma Glucose

Glucose is most informative when read alongside related markers like HbA1c and Insulin. 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 Glucose?

Glucose comes from the carbohydrates you eat (breads, pastas, fruit, sugar). Your digestive system breaks them down into glucose, which enters the bloodstream and is taken into cells with the help of insulin.

Blood glucose levels rise after meals and fall during fasting. The fasting blood glucose test (after at least 8 hours without food) measures your baseline, when insulin should be keeping blood sugar tightly controlled.

Consistently high fasting glucose suggests insulin resistance, prediabetes or type 2 diabetes. Glucose is usually tested alongside HbA1c (which shows your 2 to 3 month average) and sometimes insulin (which shows how hard your pancreas is working).

Why test Glucose?

  • To screen for and diagnose type 2 diabetes and prediabetes.
  • If you have symptoms of high blood sugar (thirst, fatigue, frequent urination).
  • If you have risk factors: family history of diabetes, central obesity, polycystic ovary syndrome (PCOS), high blood pressure, raised cholesterol.
  • To monitor diabetes alongside HbA1c.
  • As part of a wider metabolic check (heart, weight loss, biohacking panels).
To screen for and diagnose type 2 diabetes and prediabetes.

Glucose normal range (UK)

Result What it means
Below 5.5 mmol/L (fasting) Normal
5.5 to 6.9 mmol/L (fasting) Prediabetes (impaired fasting glucose)
7.0 mmol/L or above (fasting) Diabetes range
Below 7.8 mmol/L (2 hours after glucose load) Normal
11.1 mmol/L or above (any random sample with symptoms) Diabetes range

UK NHS and World Health Organization thresholds. Diagnosis of diabetes requires either a fasting glucose of 7.0 mmol/L or above on two occasions, or an HbA1c of 48 mmol/mol or above, or a single very high reading with symptoms.

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 Glucose?

  • Type 2 diabetes or prediabetes
  • Type 1 diabetes
  • Stress or acute illness (cortisol raises blood sugar)
  • Recent meal high in refined carbohydrates (if not truly fasted)
  • Some medications, especially corticosteroids
  • Pancreatic conditions
  • Cushing's syndrome and other hormonal disorders

What causes low Glucose?

  • Excess insulin (in people with diabetes who take insulin or sulphonylureas)
  • Prolonged fasting or skipped meals
  • Heavy alcohol intake on an empty stomach
  • Reactive hypoglycaemia (drop after a high carbohydrate meal)
  • Adrenal insufficiency (Addison's disease)
  • Severe liver disease
  • Insulin producing tumour (insulinoma, rare)

Symptoms of high Glucose

  • Increased thirst
  • Frequent urination
  • Fatigue and low energy
  • Blurred vision
  • Unexplained weight loss
  • Slow healing cuts and infections
  • Tingling or numbness in hands and feet

Symptoms of low Glucose

  • Shakiness or trembling
  • Sweating
  • Pale skin
  • Hunger
  • Dizziness or lightheadedness
  • Difficulty concentrating
  • Irritability or mood changes
  • In severe cases, confusion or loss of consciousness

How is Glucose tested?

Fasting glucose is measured from a small blood sample, either by finger prick at home or by a clinic blood draw.

Fast for at least 8 hours (water only) before the test. The most reliable reading is first thing in the morning after an overnight fast.

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

How to support healthy Glucose levels

  • Reduce added sugar and refined carbohydrates. Aim for whole carbohydrates with fibre, such as oats, beans, lentils and vegetables.
  • Eat protein with every meal to slow glucose absorption.
  • Move after meals. Even a 10 minute walk significantly lowers post meal glucose.
  • Resistance training improves insulin sensitivity. Aim for 2 to 3 sessions per week.
  • Prioritise sleep. Even one night of poor sleep noticeably worsens glucose regulation.
  • Manage stress. Chronic cortisol raises blood sugar.

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

Chxhealth panels that test Glucose

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

Glucose FAQs

What is a normal fasting blood glucose?

Below 5.5 mmol/L when fasted for 8 hours or more. Between 5.5 and 6.9 mmol/L is the prediabetes range, and 7.0 mmol/L or above on two occasions indicates diabetes.

How is fasting glucose different from HbA1c?

Fasting glucose is a snapshot of your blood sugar right now. HbA1c is your 2 to 3 month average. Both are used to diagnose diabetes, and together they give a richer picture than either alone.

Can stress raise blood sugar?

Yes. The stress hormone cortisol raises blood glucose to give you energy for fight or flight. Chronic stress can drive glucose into the prediabetes range even without dietary change.

Do I need to fast before a glucose test?

Yes, fast for at least 8 hours (water only). Eating or drinking anything containing calories will raise your blood sugar and make the result inaccurate.

What is reactive hypoglycaemia?

A blood sugar drop a few hours after a high carbohydrate meal, often causing shakiness, hunger and fatigue. It is most common in people with insulin resistance and improves with low glycaemic eating.

Often tested with Glucose

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

  • HbA1c: Fasting glucose and HbA1c give complementary diabetes risk views.
  • Insulin: Adding insulin reveals resistance before glucose climbs.
  • Triglycerides: Commonly elevated alongside glucose in metabolic syndrome.

Choose the right test for your goal

If you are reading about Glucose 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.