A random glucose test is one method for measuring the amount of glucose or sugar circulating in a person’s blood.

Doctors perform this test and use the result to determine whether a person is likely to have diabetes. While other tests may be necessary to confirm a full diagnosis, a random glucose test may help a doctor decide if additional testing is needed.

This article examines what a random glucose test is, why a doctor may recommend it, and what the results can mean.

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Random glucose testing measures a person’s blood glucose levels at any given point in the day. Blood glucose is also known as blood sugar.

Many blood tests for diabetes involve either fasting or continuous monitoring, but this test does not.

It is useful for people who need a speedy diagnosis, such as those with type 1 diabetes who require urgent supplementary insulin.

How does the test work?

Glucose is a form of sugar. It is the body’s primary energy source and fuels every cell — including those in the brain, heart, and muscles.

Glucose mainly comes from food and drink people consume. The body also breaks down stored forms of the carbohydrate glycogen into glucose.

The body works continuously to keep the amount of blood glucose at optimum levels. It produces a hormone called insulin to achieve this, which helps glucose get into the cells that need it for energy.

A person with type 1 diabetes does not produce insulin as their body no longer makes insulin.

Someone with type 2 diabetes either does not produce enough insulin, or their body does not respond to it appropriately.

When a person does not make insulin correctly, glucose remains in the blood. Hyperglycemia occurs when levels remain consistently high, and hypoglycemia occurs when they are too low.

Random glucose testing is one way of checking glucose levels in the blood. Doctors may perform this test at any time of day.

If the result indicates that a person has higher than expected glucose levels, the doctor will typically order a follow-up test to confirm the diagnosis. This can include:

  • Fasting glucose test: This measures blood glucose levels after the person has had nothing to eat or drink for 8 hours. Doctors usually perform this test in the morning before breakfast.
  • Oral glucose tolerance test (OGTT): People with diabetes can sometimes demonstrate normal results in the fasting or random glucose tests yet still have diabetes. If a doctor still suspects that a person has diabetes, they may recommend an OGTT. This test also requires that a person not eat or drink for 8 hours. After an initial blood sample, the individual drinks a liquid containing glucose. The doctor then takes more blood samples hourly over the next 2 hours.

A doctor may recommend a random blood glucose test if a person shows symptoms of diabetes. These symptoms may include:

Type 2 diabetes can often develop slowly, which might make initial symptoms difficult to detect.

People with diabetes may also experience a sensation of tingling or numbness in the hands or feet, called diabetic neuropathy. This is more likely to occur if a person does not control blood glucose for extended periods.

A random glucose test is a quick test that a doctor or nurse can perform at short notice in their office or clinic. The person does not need to fast beforehand.

The test requires a small blood sample using a needle, often from the finger.

Doctors measure the amount of glucose in a person’s blood in milligrams per deciliter (mg/dl).

For a random glucose test, a result of 200 mg/dl or above indicates that a person may have diabetes. However, the doctor will usually repeat the test on another day for a more reliable diagnosis.

To help confirm the diagnosis, the doctor may also order a different type of test, such as a fasting glucose test or an OGTT.

Results of a fasting glucose test indicate the following:

  • Normal: less than 100 mg/dl
  • Prediabetes: 100–125 mg/dl
  • Diabetes: 126 mg/dl or above

Results of an OGTT indicate the following:

  • Normal: less than 140 mg/dl
  • Prediabetes: 140–199 mg/dl
  • Diabetes: 200 mg/dl or above

One 2015 study suggests that one random glucose test with a reading of over 100 mg/dl is a greater risk factor for diabetes than traditional factors, such as obesity.

Prediabetes means that a person’s blood glucose levels are higher than usual, but doctors do not yet consider that they have diabetes. Doctors sometimes call this impaired glucose tolerance (IGT) or impaired fasting glucose (IFG).

People with prediabetes are at increased risk of developing diabetes. Lifestyle modifications, such as weight loss and exercise, and certain medications can help reduce this risk.

Blood glucose levels change throughout the day, depending on various factors.

These might include a person’s food intake, as well as the duration and intensity of any exercise or physical activity that day. However, people without diabetes tend to stay within the expected range of blood glucose levels.

The following factors may increase a person’s blood glucose levels:

The following factors may decrease a person’s blood glucose levels:

  • eating little or no food
  • drinking alcohol
  • medication side effects
  • intense physical activity or exercise

Diagnosis with any chronic condition can be distressing, and, without treatment, diabetes can lead to serious health problems and complications. These can include:

However, with effective treatment and management, people with diabetes can enjoy a long and active life.

Doctors usually diagnose type 1 diabetes in children and young adults. People with type 1 diabetes need to take insulin daily and regularly monitor their blood glucose levels for life.

Type 2 diabetes often develops later in life. A person can sometimes manage type 2 diabetes using only diet and exercise. Other people may need medication or insulin to keep their blood glucose levels within the healthy range.

A random glucose test measures the amount of glucose or sugar circulating in a person’s blood. They will not need to fast before the test takes place.

Doctors perform this test to determine whether a person may have diabetes. A random glucose test may help a doctor establish if additional testing is needed to make a full diagnosis.

Anyone with symptoms of diabetes should contact their doctor for an evaluation.