What Is Glucose Intolerance?

Glucose intolerance is an umbrella term for a group of metabolic conditions that result in higher than normal blood glucose (sugar) levels. This includes diabetes and prediabetes.

Glucose intolerance also refers to the conditions of impaired fasting glucose and impaired glucose tolerance. Those are different diagnoses that are based on which test revealed prediabetes.

This article looks at the various types of glucose intolerance plus their symptoms, causes, risk factors, and treatments.

Types of Glucose Intolerance 

Glucose intolerance comes in several types, including:

• Impaired fasting glucose
• Impaired glucose tolerance
• Intermediate hyperglycemia (also known as prediabetes)
• Type 2 diabetes

Impaired Fasting Glucose

Impaired fasting glucose is a stage in the natural progression toward diabetes. If you're diagnosed with this, your risk of developing diabetes is high.

This condition involves fasting glucose levels that are above normal but not high enough to be considered diabetes. Glucose values for impaired fasting glucose are:

• 100 to 125 milligrams per deciliter (mg/dL), or 5.6 to 6.9 millimoles per liter (mmol per L)

The diagnosis of impaired fasting glucose gives you an opportunity to prevent or delay the development of diabetes. Talk to your healthcare provider to come up with a plan that'll help reduce your risk.

Impaired Glucose Tolerance

Impaired glucose tolerance is known as an increased risk of developing type 2 diabetes. Many individuals do not have symptoms for a long time.

The diagnosis for impaired glucose tolerance is determined by an oral glucose tolerance test. On the 75-gram oral glucose tolerance test, the level is:

• 140 to 199 mg/dL (7.8 to 11.0 mmol)

Many people with impaired glucose tolerance already have diabetes complications by the time they're diagnosed with type 2 diabetes. It's important to tell your healthcare provider about any symptoms you notice so you can get started with treatments or preventive measures.

Intermediate Hyperglycemia (or Prediabetes)

Intermediate hyperglycemia involves both impaired fasting glucose and impaired tolerance. It's also called prediabetes.

The Centers for Disease Control and Prevention (CDC) says one in three Americans has intermittent hyperglycemia, and more than 84% don’t know they have it.

When you're at the prediabetic stage, your cells don't properly respond to insulin. The pancreas then produces more insulin to help the cells respond. When this a lot, the pancreas has a hard time producing enough insulin, and your blood sugar rises.

This is the beginning of prediabetes; if it's not managed or prevented, it can lead to type 2 diabetes.

Type 2 Diabetes

In type 2 diabetes, the body's response to insulin is further compromised and the blood sugar levels are higher. The condition can lead to a number of complications, such as:

• Kidney disease
• Vision loss
• Heart disease

If you have type 2 diabetes, it's important to work with your healthcare provider to develop and follow a treatment plan.

Symptoms of Glucose Intolerance

Glucose intolerance does not have clear symptoms, but you may have the same signs as someone with diabetes. These include:

• Constant thirst
• Fatigue
• Blurred vision
• Frequent need to urinate
• Neuropathy (tingling, pain, or numbness in your extremities)
• Slow healing from cuts and bruises

Causes and Risk Factors

The suspected causes and risk factors for glucose intolerance are essentially the same. They include:

• Age: While possible at any age, these conditions are most common in people over 45 years old.
• Obesity or being overweight: Excess body fat alters hormones and other substances in a way that contributes to problems with insulin use.
• Diet: A low-fat diet is believed to help reduce the risk and incidence of diabetes-related conditions.
• Genetics: If a parent or sibling has diabetes, your risk is higher. Genetics may also predispose you to obesity or overweightness.
• Sedentary lifestyle: Physical activity lowers blood glucose levels. Being active at least three times per week lowers your risk of insulin-related conditions.

Diagnosis of Glucose Intolerance

Several tests can diagnose glucose intolerance conditions:

• Fasting plasma glucose (FPG) test: Your blood is drawn and glucose levels tested after you've fasted for at least 8 hours.
• Two-hour oral glucose tolerance test (GTT): You drink a sugary drink and have your blood drawn and tested two hours later.
• Glycated hemoglobin (A1C or HbA1C): Your blood is drawn and tested to get an average blood glucose level for the past three months.
• Random plasma glucose test: Your blood is drawn and tested at a time when you have severe diabetes symptoms.

The results of these tests will help your healthcare provider determine which condition you have.

Treatment of Glucose Intolerance

Conditions involving glucose intolerance are treated with lifestyle changes and, if needed, medication.

Lifestyle Changes

You may be able to fully control your glucose intolerance with changes to three elements of your lifestyle:

• Diet: Three meals a day at consistent times can keep blood sugar levels steady. Avoid alcohol and foods high in fat or sugar. Focus on whole grains, fruits, and vegetables.
• Exercise: Exertion lowers blood sugar levels and helps you reach or maintain a healthy weight.
• Reach or maintain a healthy weight: Fat impairs insulin use, so losing weight improves insulin use and blood sugar levels.

An added bonus is that these changes are also considered heart-healthy.

Medications

Not everyone can control their glucose intolerance through lifestyle changes. In those cases, medication becomes necessary. The two main types are:

• Oral medications: These help your body produce insulin and use it more effectively. A common one is Glucophage (metformin).
• Insulin: Directly injecting insulin into your body provides more for your body to use. Insulin comes in slow-acting and fast-acting forms.

You inject insulin at home either on a set schedule or to correct high blood glucose readings. Your healthcare provider or a diabetic educator will help you understand how to use and adjust your insulin.

Summary

Glucose intolerance is an umbrella term for impaired fasting glucose, impaired glucose tolerance, prediabetes, and type 2 diabetes. Symptoms may be absent or may include diabetes symptoms such as excessive thirst, fatigue, and frequent urination.

Causes and risk factors include age, weight, genetics, and lifestyle factors. Several tests can diagnose these conditions. Treatment typically includes dietary changes, more exercise, losing weight and, if necessary, medications.

A Word From Verywell

If you have symptoms of glucose intolerance, it is important to have a conversation with your healthcare provider. They can help guide you in the right direction and create a proper plan so you can manage your condition and have a healthy outcome.