Blood Sugar Levels: Ranges, Symptoms, Testing & Control

Blood sugar provides the body with an essential source of energy, but levels that are too high or too low can affect health. Blood glucose naturally changes throughout the day and can be influenced by food, activity, insulin, health conditions, and other factors.

This guide explains healthy blood sugar ranges, how glucose is measured, what abnormal values may indicate, and how testing and everyday habits can help you better understand and manage your blood sugar.

Table of Contents

• What are blood sugar levels?
• Who should measure their blood sugar level?
• How is blood sugar measured?
• What blood sugar level indicates diabetes?
• What is a healthy blood sugar level?
• Symptoms of high blood sugar
• Symptoms of low blood sugar
• What should you do if your blood sugar level is high?
• What should you do if your blood sugar level is low?
• How can you control your blood sugar levels?
• Summary

What are blood sugar levels?

Blood sugar level refers to the concentration of glucose (sugar) in the blood. Your blood sugar level changes throughout the day, depending on what you eat and drink. Blood sugar ensures the supply of energy to your cells, which is why blood sugar must not drop too low. A low blood sugar level is also referred to as hypoglycaemia. Low blood sugar leads to hunger, dizziness, fatigue, and sweating. Shock and seizures may also occur. Conversely, a blood sugar level that is too high (hyperglycaemia) can, over time, damage blood vessels and cause health problems such as diabetes, kidney disease, or heart disease (CDC, 2022).

Who should measure their blood sugar level?

People with diabetes

If you have diabetes, it is necessary to regularly check your blood sugar level. Diabetes is a condition in which there is too much glucose (sugar) in the blood. This may occur, for example, when the body does not produce insulin or cannot use it properly (CDC, 2022). Insulin is a hormone that transports glucose in the blood into the body’s cells for energy. If not enough insulin is produced, or if insulin resistance is present, glucose accumulates in the blood, causing blood sugar levels to rise. There are two types of diabetes: type 1 and type 2.

Type 1 diabetes: Type 1 diabetes is an autoimmune disease in which the body does not produce insulin. People with type 1 diabetes must take insulin for life to regulate their blood sugar. This is done either through injections or an insulin pump. Type 1 diabetes usually develops in younger people but can also be diagnosed in adults.

Type 2 diabetes: Type 2 diabetes occurs when the body either does not produce enough insulin or cannot use it properly. Unlike type 1 diabetes, type 2 diabetes can be treated without insulin by making lifestyle changes, such as weight loss, a healthy diet, and more physical activity.

People without diabetes

Diabetes can develop gradually and is often only noticed when serious symptoms occur. Therefore, even people who are not diagnosed with diabetes but may be at risk should regularly monitor their blood sugar levels. This helps to detect abnormalities or disorders early (CDC, 2022). Risk factors for type 2 diabetes include:

• Overweight

• Prediabetes

• Age over 45

• A parent or sibling with type 2 diabetes

• Gestational diabetes

• Low physical activity

• Belonging to certain ethnic groups, including: Black, Turkish, South Asian, or Moroccan. Certain ethnic groups are at higher risk of developing type 2 diabetes at a younger age.
  Source: Thuisarts, 2021, CDC, 2022

While type 1 diabetes is not curable, type 2 diabetes can be prevented. Regular exercise, a balanced diet, and maintaining a healthy body weight can improve the body's sensitivity to insulin. It is also important to detect slightly elevated blood sugar levels at an early stage (prediabetes) before diabetes develops. Measuring blood sugar levels in non-diabetics can help diagnose diabetes before noticeable symptoms occur and enable treatment before complications arise.

How is blood sugar measured?

Various types of blood sugar tests are available for diagnosing and monitoring diabetes. For people with diabetes, it is important to regularly measure their blood sugar to ensure their diabetes is well managed.

Self-monitoring of blood sugar

Depending on the type of diabetes and treatment plan, people with diabetes may need to measure their blood sugar several times a day. Self-monitoring helps individuals understand how their body responds to food, exercise, and medication and allows them to keep their blood sugar within a healthy range. Blood sugar can be measured with a glucose meter that uses a small drop of blood, usually from the fingertip. A continuous glucose monitor (CGM) can also be used. CGMs are devices worn on the skin that continuously monitor blood sugar levels without the need for finger pricks (CDC, 2022).

Fasting blood sugar test

According to the NHG guideline, the fasting blood sugar test (fasting plasma glucose) is the preferred glucose measurement for detecting and diagnosing diabetes mellitus. “Fasting” means that the patient has had no caloric intake for at least 8 hours. The diagnosis should be based on plasma glucose values, preferably measured in venous plasma by a laboratory.

Diabetes mellitus is diagnosed with 2 fasting plasma glucose values ≥ 7.0 mmol/L on 2 different days. It can also be diagnosed with 1 fasting value ≥ 7.0 mmol/L or a random value ≥ 11.1 mmol/L when symptoms of hyperglycaemia are present. Impaired fasting glucose or glucose tolerance indicates increased diabetes and cardiovascular risk; repeat fasting laboratory glucose after 3 months and then annually if diabetes is not diagnosed. Marginally abnormal finger-prick results should be confirmed with a laboratory plasma glucose test because glucose meters may have a 10–15% measurement error.

Source: NHG, 2026

Glucose tolerance test

A glucose tolerance test assesses whether the body can process glucose normally. Blood sugar levels are measured before and after drinking a glucose-rich beverage. This test can diagnose diabetes or gestational diabetes (diabetes during pregnancy). Blood sugar is measured in a fasting state (after fasting for 8–12 hours), followed by another measurement 1, 2, or 3 hours after drinking the glucose solution (Mayo Clinic, 2023). The threshold for diabetes in this test depends on the time of measurement and whether the patient is pregnant.

Random blood sugar test (non-fasting)

This test measures your blood sugar at the time of testing and can also be used to diagnose diabetes. You do not need to fast before this test. A non-fasting blood sugar value above 11 mmol/l (200 ng/dl) may indicate diabetes (Mayo Clinic, 2023).

HbA1c test

HbA1c (glycated haemoglobin) reflects the average blood glucose level over approximately the previous 3 months. It forms when glucose binds to haemoglobin in red blood cells; therefore, higher average glucose levels generally result in a higher HbA1c value.

According to the NHG Standard Diabetes mellitus type 2, HbA1c should not be used to screen for or diagnose diabetes mellitus. Diagnosis is based on plasma glucose measurements. HbA1c is mainly used after diagnosis to monitor glycaemic control and guide treatment.

Source: NHG, 2026

With Homed-IQ’s blood sugar test, you can also determine your HbA1c level at home. This test involves taking a blood sample from your finger and sending it to a lab for analysis.

What blood sugar level indicates diabetes?

• Diabetes: fasting plasma glucose ≥ 7.0 mmol/L on 2 different days.
• Diabetes: fasting plasma glucose ≥ 7.0 mmol/L or random plasma glucose value ≥ 11.1 mmol/L with symptoms.
• Impaired glucose levels: disturbed fasting glucose value and a disturbed glucose tolerance increase the risk of diabetes and cardiovascular disease.

Source: NHG, 2026

What does mmol/l and ng/ml mean?

Mmol/l stands for millimoles per litre and is a unit used to express the concentration of substances in a given amount of liquid. Depending on the country, either mmol/l or mg/dl (milligrams per decilitre) is used to express blood sugar levels. For example, a blood sugar level of 5 mmol/l means that there are 5 millimoles of glucose per litre of blood, or 90 milligrams per decilitre.

What is a healthy blood sugar level?

A healthy blood sugar level (for a non-diabetic) is generally:

• below 6.1 mmol/L when fasting and below 7.8 mmol/L when not fasting.
  

The thresholds for diagnosing diabetes may vary, and test results should be interpreted by a doctor. 

Source: NHG, 2026

Symptoms of high blood sugar

High blood sugar (hyperglycemia) occurs when the level of glucose in the blood is too high. High blood sugar is the main symptom of Type 1 and Type 2 diabetes, but it can also occur in people who have certain chronic diseases, are stressed, or are ill. Lack of physical activity, insufficient insulin intake (in diabetics), overeating, dehydration, unhealthy diet, and irregular meals can all cause high blood sugar (NHS, 2022).

The symptoms of high blood sugar are usually subtle at first and only appear when levels become very high. The symptoms of high blood sugar are the same as the symptoms of untreated diabetes, which leads to high blood sugar due to a lack of insulin. Symptoms may include:

• Extreme thirst

• Frequent urination

• Weight loss

• Blurred vision

• Fatigue

• Recurrent infections such as thrush, bladder infections, and skin infections

A very high blood sugar level can lead to life-threatening complications such as diabetic ketoacidosis (DKA). Ketones are a chemical substance produced by the liver when it breaks down fat. Your body uses ketones during fasting, prolonged exercise, and when few carbohydrates are available. If your body does not have enough insulin, it starts turning fat into energy instead of using blood sugar. This process creates ketones, which accumulate in the blood and can lead to DKA. This is a medical emergency and must be treated immediately (NHS, 2022).

Symptoms of DKA include:

• Fruity-smelling breath

• Thirst

• Fainting

• Feeling unwell

• Frequent urination

• Confusion

• Coma

Symptoms of low blood sugar

Low blood sugar is defined as a blood glucose level below 3.5 mmol/L (CDC, 2021). Hypoglycemia most commonly occurs in people with Type 1 diabetes and can be caused by too much insulin, too few carbohydrates for insulin uptake, changes in daily routine, hot weather, or alcohol consumption.

The symptoms of low blood sugar vary from person to person. For diabetics, it is important to recognize their own signs of hypoglycemia. Symptoms may include:

• Hunger

• Dizziness

• Rapid heartbeat

• Nervousness

• Shaking

• Sweating

• Irritability or confusion

Some people do not experience symptoms of low blood sugar until levels become dangerously low. This is known as hypoglycemia unawareness and can occur in people who have had diabetes for a long time, frequently have low blood sugar, or take certain medications (CDC, 2021). People who are unaware of their hypoglycemia may need to monitor their blood sugar more frequently.

What should you do if your blood sugar level is high?

If you have diabetes, it is important to prevent your blood sugar level from rising too much. You can do the following:

• Contact your doctor: They can advise you on how to manage your blood sugar over time and adjust your insulin dose if necessary.

• Monitor your blood sugar: Check your levels regularly and discuss changes with your doctor.

• Take diabetes medication as prescribed: Make sure to follow the instructions given by your doctor or care team.

• Drink enough fluids (sugar-free): Dehydration can lead to high blood sugar.

• Reduce intake of sugary or starchy foods: These foods are high in carbohydrates, which can quickly raise blood sugar.

• Exercise regularly: Aim to be active for at least 30 minutes a day. Strength and endurance training should be part of your routine.
  Source: NHS, 2023

Keep in mind that a high blood sugar level over time can damage organs and tissues. If your blood sugar is too high, you should consult your doctor and discuss how to best manage it. Some people can control their blood sugar through lifestyle changes such as diet and exercise, while others may need medication to maintain a healthy level.

What should you do if your blood sugar level is low?

Hypoglycaemia occurs when your blood sugar level drops too low. This mainly affects people with diabetes who take insulin. Low blood sugar can be dangerous and requires immediate action to raise it. Here are a few steps you can take:

• Eat or drink fast-acting carbohydrates: These include sugar, honey, glucose tablets, juice, candy, or soda (not diet).

• Monitor blood sugar: Check your level 10 minutes after consuming fast-acting carbohydrates. If there is no change, take more and check again after 10–15 minutes.

• Eat a snack or meal: Once your blood sugar returns to normal, eat a meal or snack containing slowly released carbohydrates (e.g., whole grain bread with cheese) to prevent another drop.

• Talk to your doctor: If you have a very low blood sugar or frequent episodes, speak to your doctor. They may need to adjust your treatment plan.
  Source: NHS, 2020

How can you control your blood sugar levels?

Maintaining a normal blood sugar level is important to prevent type 2 diabetes and to ensure that people with diabetes keep their levels stable. Tips for controlling blood sugar levels include:

• Eat a healthy, balanced diet rich in vegetables, fruits, whole grains, and protein.

• Maintain a healthy weight.

• Exercise regularly.

• Avoid stress.

• Check your blood sugar levels regularly.

• Eat at regular times and do not skip meals.

• Avoid alcohol, juice, and soda.
  Source: CDC, 2022

If you have diabetes, it is important to work closely with your doctor to regulate your blood sugar. This can help prevent complications in the future and allow you to live a healthy and active life.

Summary

Blood sugar levels are an important indicator of how the body processes and uses glucose. Understanding normal ranges, testing methods, and the signs of high or low blood sugar can help identify changes that may require further attention.

Whether you have diabetes, are at increased risk, or simply want to understand your metabolic health better, regular monitoring and healthy lifestyle habits can provide valuable insight into blood sugar control.