Blog - Diabetes Information, Symptoms & Diagnoses
Blood glucose levels: normal ranges and testing
Our bodies rely on both glucose and insulin for survival. We absorb glucose from the food we eat and then insulin from the pancreas enables our cells to use this glucose to generate energy. In diabetes, this process is disrupted, and the cells cannot access glucose in the same way, if at all. As a result, glucose builds up in the bloodstream, leading to high blood sugar levels.
There are different reasons why this can happen. In type 1 diabetes (sometimes referred to as insulin-dependent diabetes), the pancreas produces no, or very little insulin. A person with type 1 diabetes must regularly inject insulin so their cells can use the circulating glucose. In type 2 diabetes, the body fails to make enough insulin, or the cells become resistant to insulin, causing high blood sugar levels.1
A continuous glucose monitoring system (CGM) such as Dexcom real-time CGM systems can simplify the way people with diabetes track their glucose. The automated sensor readings help to stay within target range. CGMs measure glucose in the interstitial fluid, replacing traditional finger prick tests‡ which measures the blood sugar levels2,3,4
What is a normal blood glucose level?
Blood glucose levels fluctuate throughout the day, influenced by various factors, including when and what we eat, alcohol intake, exercise, and stress. It’s normal to have raised blood sugar levels after eating, although for non-diabetic people, the body typically keeps blood glucose stable and within a healthy blood sugar range.
In the UK, blood glucose is measured in millimoles per litre (mmol/L). Ordinarily, normal blood sugar levels for non-diabetic people remain stable between 4 mmol/L and 6 mmol/L.5
Optimal blood sugar levels for people with diabetes
If you have type 1 or type 2 diabetes, your target blood sugar range can vary depending on several factors including age, overall health, underlying health conditions, pregnancy, or religious fasting.
Your diabetes specialist or healthcare provider will set you a target range. However, as a guide only, the accepted blood sugar targets for non-pregnant adults with type 1 or type 2 diabetes are 6,§:
- Before a meal (preprandial): 4.4 mmol/L – 7.2 mmol/L
- 1-2 hours after eating (postprandial): <10.0 mmol/L
How are blood glucose levels traditionally tested?
There are several ways of testing blood glucose levels, each with its own uses and limitations.
HbA1c test
The hemoglobin A1C (HbA1c) is known as glycated haemoglobin, and it is the fraction of haemoglobin in your red blood cells that has sugar attached. The HbA1c test measures this fraction and is a good biomarker for your average blood sugar level for the previous three months. The higher your HbA1c result the higher your average blood sugar level. Based on the HbA1c the estimated average glucose (eAG) or glucose management indicator (GMI) was introduced7, translating the HbA1c in an average level based on the measurements of your CGM. Unlike blood glucose tests that give a snapshot of blood sugars at that moment, the HbA1c and eAG/GMI provide a broader view of your glucose level, allowing doctors to spot patterns and early signs of diabetes.
Fasting blood sugar test
A fasting blood sugar test is a blood test taken first thing in the morning, before eating or drinking, to check your blood sugar levels after fasting overnight. Ideally, your blood sugar should remain within normal parameters. This test helps to assess the effectiveness of your current diabetes management.
Glucose tolerance test
A glucose tolerance test involves checking blood sugar levels after an overnight fast and then again 1-2 hours after drinking a high-glucose drink. Your doctor will compare the two results to see how your body copes before and after consuming glucose.
Random blood sugar test/Finger pricks
You can perform a random blood sugar test at any time you want to check your blood glucose level without the need for fasting. This allows people with diabetes to regularly test and manage their blood sugars without attending a clinic or healthcare setting. CGMs measure the glucose under the skin in the body tissue and replace finger pricks‡ (random blood sugar test) as the emerging new standard of care.2,3,4
Glucose level charts
The following chart shows the typical parameters for each blood sugar test8,§.
Normal | Prediabetes | Diabetes | |
A1c test | < 5.7% | 5.7 - 6.4% | > 6.5% |
Fasting blood glucose test | < 5.5 mmol/L | 5.6 mmol/L – 6.9 mmol/L | > 7.0 mmol/L |
Glucose tolerance test | < 7.7 mmol/L | 7.8 mmol/L – 11.0 mmol/L | > 11.1 mmol/L |
Random blood sugar test | N/A | N/A | > 11.1 mmol/L |
What is a healthy glucose range for under 18s with type 1 diabetes?
Diabetes management for children and adolescents differs significantly from that of adults with diabetes9. The following glucose chart shows the ideal blood glucose level parameters in children under 18 with type 1 diabetes4, §:
Blood sugar level before eating (preprandial) | Blood sugar level 1-2 hours after eating (postprandial) |
4.0 - 7.0 mmol/L | < 9.0 mmol/L |
Physical exercise benefits overall health in those with type 1 diabetes10. However, it can also impact blood glucose levels and cause hypoglycaemia or hyperglycaemia, so robust diabetes management is vital. Children must check their sugar levels more frequently than adults, particularly during and after exercising every 30 minutes11.
A Dexcom CGM can support children and adolescents with type 1 diabetes to improve glucose control, reduce the risk of hypoglycaemia, hyperglycaemia or diabetic ketoacidosis.
What is a healthy blood sugar range for under 18s with type 2 diabetes?
Children with type 2 diabetes may be more susceptible to health complications such as12
- Obesity
- Ketosis (raised levels of ketones in blood or urine. You can check levels at home or with your healthcare provider)
- Hypoglycaemia or hyperglycaemia
- Hyperosmolar hyperglycaemic state (HHS).
Healthy eating and regular exercise can help people with type 2 diabetes manage their condition and maintain optimal health.
Both children and adolescents with type 2 diabetes are advised to undergo regular A1C testing, to monitor the effectiveness of current diabetes management. Doctors assess these test results, alongside lifestyle and health factors, to support the patient and develop a treatment plan10.
Recommended HbA1c levels for children and adolescents are as follows13, §:
- HbA1c level < 53 mmol/mol (< 7%) is a reasonable target for most children and adolescents on oral medication alone.
- HbA1c level < 48 mmol/mol (< 6.5%) may be a suitable target if it does not pose a significant risk of hypoglycaemia or other adverse effects of treatment.
- HbA1c level 58mmol/L (7.5%) or thereabouts if there is an increased risk of hypoglycaemia.
Important: In all cases, glucose targets must be agreed upon with your diabetes specialist.
Frequent sugar monitoring at home is vital for effective diabetes care. The Dexcom Continuous Glucose Monitoring system helps people with type 2 diabetes monitor and manage their glucose levels10.
Blood glucose ranges during pregnancy
If your midwife or doctor considers you at risk of gestational diabetes, they will offer you a screening test when you are 24-28 weeks pregnant. A high result can indicate gestational diabetes, a specific type of diabetes that occurs during pregnancy. (High blood sugar detected in early pregnancy suggests type 1 or type 2 diabetes rather than gestational diabetes.)
Target glucose levels in pregnancy for women with any type of diabetes13, §:
Blood sugar level before eating (preprandial) | Blood sugar level 2 hours after eating (postprandial) |
< 5.3 mmol/L | < 6.4 mmol/L |
Pregnant women with diabetes who are taking insulin should maintain their blood sugar levels above 4 mmol/L13.
Find the right Dexcom CGM for you
Dexcom continuous glucose monitoring systems are designed to make diabetes management easier and safer, whatever your age, lifestyle, daily routine or health status.
Dexcom CGMs are proven to improve glycaemic control10,14,15,16,17,18. CGM use for people with diabetes in pregnancy is recommended to reduce the risk of complications10. Get accurate||, real-time glucose readings, set up alerts and share¶ your results with family or friends, without the need for finger pricks†,‡.
NB: Blood sugar level conversions between US and UK measurements calculated at: https://www.diabetes.co.uk/blood-sugar-converter.html
†Display devices sold separately. For a list of compatible smart devices, please visit www.dexcom.com/en-GB/compatibility.
‡Finger pricks are required for diabetes treatment decisions if symptoms or expectations do not match readings
§ Measurement has been converted from mg/dL to mmol/L. Available at Blood Sugar Converter, diabetes.co.uk. Last reviewed on June 10, 2022.
|| Please refer to G6, Dexcom ONE and G7 User Guide.
¶ Following requires an internet connection and the Dexcom Follow app.
2 NICE. Type 1 diabetes in adults: diagnosis and management NICE guideline [NG17]. Updated 17 August 2022. Accessed 10 January 2023. NICE.
3 NICE. Type 2 diabetes in adults: management NICE guideline [NG28]. Updated 29 June 2022. Accessed 10 January 2023. NHS.
4 NICE. Diabetes (type 1 and type 2) in children and young people: diagnosis and management NICE guideline [NG18]. Updated 29 June 2022. Accessed 10 January 2023. NICE.
5 Mathew TK, et al. Blood Glucose Monitoring. StatPearls Publishing. Updated 8 August 2022. . Accessed 10 January 2022. National Library of Medicine.
6 American Diabetes Association. The Big Picture: Checking Your Blood Glucose. Accessed 10 January 2023. Diabetes.org.
7 Klonoff DC. ADAG Study Group Data Links A1C Levels with Empirically Measured Blood Glucose Values- New Treatment Guidelines Will Now be Needed. J Diabetes Sci Technol. 2014;8(3):439-443.
8 Centers for Disease Control and Prevention. Diabetes Tests. Updated 10 August 2021. Accessed 10 January 2023. CDC.
9 Iyengar J, et al. Transition from pediatric to adult care in emerging adults with type 1 diabetes: a blueprint for effective receivership. 2019;5(3). Clinical Diabetes and Endocrinology.
10 Martens T, et al. Effect of continuous glucose monitoring on glycemic control in patients with type 2 diabetes treated with basal insulin: A randomized clinical trial. JAMA. 2021;325(22):2262-2272.
11 Mayo Clinic. Diabetes and exercise: When to monitor your blood sugar. Updated 20 January 2022. Accessed 10 January 2023. Mayo Clinic.
12 Diabetes Care. 13. Children and Adolescents: Standards of Medical Care in Diabetes—2021.2021;44(1): S180-S199. American Diabetes Association.
13 NICE. Diabetes in pregnancy: management from preconception to the postnatal period ([NG3]. Updated 16 December 2020. Accessed 10 January 2023. NICE.
14 Beck RW, et al. Effect of continuous glucose monitoring on glycemic control in adults with type 1 diabetes using insulin injections: The DIAMOND randomized clinical trial. JAMA. 2017;317(4):371-378.
15 Beck RW, et al. Continuous glucose monitoring versus usual care in patients with type 2 diabetes receiving multiple daily insulin injections: A randomized trial. Ann Intern Med. 2017;167(6):365-374.
16 Šoupal J, et al. Glycemic Outcomes in Adults with T1D Are Impacted More by Continuous Glucose Monitoring Than by Insulin Delivery Method: 3 Years of Follow‐Up from The COMISAIR Study. Diabetes Care. 2020;43:37-43.
17 Welsh JB, et al. Comparisons of Fifth-, Sixth-, and Seventh-Generation Continuous Glucose Monitoring Systems. J Diabetes Sci Technol. 2022:19322968221099879.
18 Lind M, et al. Continuous Glucose Monitoring vs Conventional Therapy for Glycemic Control in Adults With Type 1 Diabetes Treated With Multiple Daily Insulin Injections: The GOLD Randomized Clinical Trial. JAMA. 2017;317(4):379-387.