Fasting Blood Glucose Test: Purpose, Preparation, and Normal Levels

What is fasting blood sugar?

A fasting blood sugar test measures how much glucose (sugar) is in your blood after fasting for at least 8 hours. This test helps doctors assess how well your body manages blood sugar and can identify conditions like diabetes and prediabetes early on.

During an overnight fast, your body isn't processing food. The test provides a clear picture of your body's baseline blood sugar levels.

Even when you're not eating, your liver releases stored glucose to maintain your blood sugar. If these levels are too high even during fasting, it may signal health problems that need attention.

How does blood glucose work?

Blood glucose is your body's main source of energy.

When you eat foods containing carbohydrates (such as bread, rice, fruits, and pasta), your body breaks them down into glucose. This glucose enters your bloodstream and raises your blood sugar levels.

The role of insulin

• Your pancreas detects the rising blood sugar and releases insulin hormone.

• Insulin helps move glucose from your blood into your body's cells.

• Your cells then use this glucose for energy or store it for future use.

What happens when blood glucose regulation fails?

• In type 1 diabetes, the body produces little to no insulin.

• In type 2 diabetes, the body is resistant to insulin or doesn't produce enough.

• When glucose can't enter cells, it accumulates in the blood, causing high blood sugar levels that can lead to serious health issues over time.

Your body normally keeps blood glucose levels within a healthy range by balancing food intake with insulin action.

Normal fasting blood sugar level vs. Diabetes blood sugar level

Doctors compare your fasting blood glucose to standard ranges to see how well your body manages blood sugar. These ranges help identify whether you have normal blood glucose, prediabetes, or diabetes.

Fasting blood glucose ranges for diagnostic classification

Note: These guidelines are specific to Singapore's healthcare standards.

Who should get a fasting blood glucose test?

Doctors recommend this test for:

• Adults over 35, especially those with risk factors like:

  • Obesity

  • Family history of diabetes

  • High blood pressure

  • Sedentary lifestyle

• Pregnant women who may develop gestational diabetes due to hormonal changes during pregnancy.

• People showing signs of high blood sugar (hyperglycemia):

  • Increased thirst

  • Frequent urination

• Individuals with conditions like PCOS or history of gestational diabetes

• Anyone during routine annual check-ups

• People with previous tests indicating higher-than-normal results

It's important to know that prediabetes, type 2 diabetes, and gestational diabetes often have no symptoms in their early stages. You might have one of these conditions without knowing it, which is why testing is important.

If you are experiencing any of these symptoms, request an appointment with Thomson Medical. Our specialists can assist with further diagnosis, including a fasting blood glucose test, to determine the cause of your symptoms and provide an appropriate treatment plan.

How do I prepare for a fasting blood sugar test?

Preparing for a fasting blood test of glucose is simple but important for correct results.

• Fasting duration

  • Don't eat or drink anything except water for at least 8 hours before your test.

• Avoid physical stress

  • Don't do heavy exercise right before the test, as the activity can affect your blood sugar levels.

• Medication guidance

  • Take your regular medications as usual unless your doctor advises otherwise.

What can I expect on the day of the test?

 Your fasting blood glucose test is a quick, simple procedure. Here's what will happen:

• Arrival at the clinic/lab

  • On the day of the test, you'll check in at the clinic or lab and complete any necessary paperwork for registration.

• Blood sample collection

  • A healthcare worker will clean a spot on your arm and insert a small needle into a vein to collect blood.

• Sample processing

  • After collection, they'll send your blood sample to the laboratory for testing.

• Post-test routine

  • You can eat and drink normally and can continue your daily activities right after the test.

• Results timeline

  • Most results are ready within a day. Your doctor will explain what your reports say.

Are there any risks with a fasting blood sugar test?

The test is very safe, with only a few minor possible side effects:

• You might get a small bruise where the needle went in your arm

• Some people feel dizzy or light-headed during blood draws, but this doesn't happen often

• There's a minimal chance of infection where the skin was punctured, but proper cleaning before the test makes this rare.

FAQ

What is a normal glucose level when fasting?

A normal level of fasting blood glucose is usually less than 5.6 mmol/L in Singapore. The level of glucose is usually assessed through routine blood tests, where a sample of blood is taken after fasting for at least 8 hours.

What is a normal blood sugar level without fasting?

For a random blood glucose test in Singapore, a healthy blood sugar level should be less than 7.8 mmol/L. This threshold can vary depending on when you last ate and is an important part of monitoring blood glucose levels.

What are five signs that your blood glucose is too high?

1. Frequent urination

2. Increased thirst

3. Blurred vision

4. Fatigue

5. Slow-healing wounds

If you experience these symptoms, contact your healthcare provider. They may recommend blood glucose testing or a diabetes screening test to check for the type of diabetes, as these are common symptoms of the condition.

How can I reduce my blood sugar level immediately?

• Engage in light physical activity (like walking).

• Drink plenty of water to help flush out excess sugar.

• If blood glucose levels are significantly high, seek immediate medical attention.

Can drinking water lower blood sugar?

Yes, drinking water helps flush excess glucose through urine, which can help regulate blood sugar levels.

Is 6.3 considered diabetic?

• HbA1c Levels

  • HbA1c reflects your average blood sugar levels over the past 2–3 months. An HbA1c of ≥ 6.3% (45 mmol/mol) is a sign of diabetes mellitus.

• Fasting Blood Sugar

  • A fasting blood sugar level of 6.3 mmol/L falls within the impaired fasting glucose range, indicating an increased risk of developing diabetes. This level is not considered diabetic but suggests prediabetes.

Regular blood testing, including glucose tolerance tests or continuous glucose monitoring, can help assess your risk and manage diabetes if diagnosed.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations based on your medical conditions, request an appointment with Thomson Medical.