What Causes Blood Sugar to Rise in Non-Diabetics?

High blood sugar, also called hyperglycemia, occurs when there is too much glucose in the blood. High blood sugar is the [primary symptom that underlies diabetes], but it can also occur in people who don’t have type 1 or type 2 diabetes, either because of stress or trauma, or gradually as a result of certain chronic conditions.

It is important to manage high blood sugar, even if you don’t have diabetes, because elevated blood glucose can delay your ability to heal, increase your risk of infections, and cause irreversible damage to your nerves, blood vessels, and organs, such as your eyes and kidneys. Blood vessel damage from high blood sugar also increases your risk of heart attack and stroke.

High Blood Sugar Causes in People Without Diabetes - Illustration by Jessica Olah

Verywell / Jessica Olah

Non-Diabetic Hyperglycemia and Prediabetes

You are considered to have impaired glucose tolerance or prediabetes if you have a fasting glucose level between 100–125 mg/dL. If your fasting blood glucose level is greater than 125 mg/dL, or greater than 180 mg/dL one to two hours after eating, that is considered hyperglycemia.

The body obtains glucose mainly by consuming carbohydrates, but also through the breakdown of glycogen to glucose—a process called glycogenolysis—or conversion of non-carbohydrate sources to glucose—called gluconeogenesis—that primarily occurs in the liver.

While 50% to 80% of glucose is used by the brain, kidneys, and red blood cells for energy, the remaining supply of glucose is used to produce energy. It is stored as glycogen in the liver and muscles, and can be tapped into at a later time for energy or converted into fat tissue.

In healthy people, blood glucose levels are regulated by the hormone insulin to stay at a steady level of 80–100 mg/dL. Insulin maintains steady blood sugar by increasing the uptake and storage of glucose and decreasing inflammatory proteins that raise blood sugar when there is an excess of glucose in the blood.

Certain conditions can increase your blood glucose levels by interfering with the ability of insulin to transport glucose out of the bloodstream. When this occurs, you develop hyperglycemia, which puts you at an increased risk of prediabetes, diabetes, and related complications.

Common Causes

Causes of high blood sugar in non-diabetics include:

Cushing’s Syndrome

Cushing’s syndrome results from excess secretion of the adrenocorticotropic hormone, a hormone produced in the anterior (back) portion of the pituitary gland. This hormone that causes excess cortisol to be produced and released from the adrenal glands. Pituitary adenomas, or tumors of the pituitary gland, are the cause of Cushing’s syndrome in more than 70% of cases. Prolonged use of corticosteroid medication can also significantly increase the risk.

People with Cushing’s syndrome are at an increased risk of developing decreased glucose tolerance and hyperglycemia as a result of increased levels of cortisol throughout the body. Cortisol is a hormone that counteracts the effects of insulin by blocking the uptake of glucose from the bloodstream. This increases insulin resistance and maintains high blood sugar levels. Elevated cortisol levels also partially decrease the release of insulin from where it is produced in the pancreas.

Approximately 10% to 30% of people with Cushing’s syndrome will develop impaired glucose tolerance, while 40% to 45% will develop diabetes.

Corticosteroid medication is often prescribed to decrease inflammation throughout the body. However, corticosteroids can lead to the development of Cushing’s syndrome and hyperglycemia because they activate specific enzymes. These enzymes can convert non-carbohydrate molecules into glucose (gluconeogenesis). Corticosteroids also disrupt pancreatic cell function by interfering with cell signaling pathways involved in the release of insulin from the pancreas.

Pancreatic Diseases

Pancreatic diseases such as pancreatitis, pancreatic cancer, and cystic fibrosis can cause hyperglycemia because pancreas cells are damaged in these conditions. Insulin is produced and released from the cells of the pancreas. With inflammation and damage to the pancreas, pancreatic cells are no longer able to produce enough insulin to remove glucose from the blood to control blood sugar.

Polycystic Ovarian Syndrome

Polycystic ovary syndrome (PCOS) is a condition that causes irregular, often heavy menstrual periods. It is a common endocrine disorder among women of reproductive age. Women with PCOS have hormonal imbalances, such as increased levels of testosterone, insulin, and inflammatory proteins called cytokines released from fat tissue.

Despite increased levels of insulin, women with PCOS exhibit insulin resistance since their insulin hormones cannot adequately uptake glucose or utilize it for energy. Insulin receptors in women with PCOS cannot efficiently bind to insulin. Because insulin transports glucose, excess glucose remains in the bloodstream, producing hyperglycemia.


Physical stress to the body, including trauma, burns, and other injuries, can cause high blood sugar by altering the way glucose is metabolized. Stress-induced hyperglycemia results when physical stressors to the body stimulate increased activity of the sympathetic nervous system, the body’s fight-or-flight response, to release cytokines and hormones that counteract the effects of insulin in removing excess glucose from the bloodstream.

These cytokines and hormones like epinephrine increase the production of glucose through the breakdown of glycogen stores into glucose (glycogenolysis) and conversion of non-carbohydrate sources into glucose (gluconeogenesis).

Increased levels of the stress hormone cortisol, which is also released, block the effects of insulin from taking glucose from the bloodstream into cells, further contributing to high blood sugar.

Surgery and Stress

Alterations to glucose metabolism that occur from physical stress to the body also occur after surgery. Surgery is a controlled form of stress to the body that results in similar increases in cytokines and hormones that drive the production of glucose in the liver and block the effects of insulin from removing excess glucose from the blood.

Up to 30% of patients can develop stress-induced hyperglycemia after surgery, with blood glucose levels that stay elevated long after returning home from the hospital. Elevated blood sugar after surgery can have significant effects on overall health and increases the risk of developing diabetes and other serious conditions.


Stress-induced hyperglycemia can also result from the physical stress of having an infection, such as pneumonia or urinary tract infections. Increased levels of the stress hormone cortisol that occurs with infections block the ability of insulin to remove excess glucose from the bloodstream, keeping the body in a state of high blood sugar.

High blood glucose also results from infections as a normal reaction in order to support the needs of organs like the brain, kidneys, and red blood cells that depend on glucose for energy to aid in the immune system’s response to fight off an infection.

Medication Side Effects

Certain medications—such as catecholamine vasopressors like dopamine and norepinephrine, immunosuppressants like tacrolimus and cyclosporine, and corticosteroids—can increase blood glucose levels by activating enzymes that increase blood glucose levels and disrupting the release and activity of insulin to uptake glucose from the blood.

Hospitalized patients receiving nutrition through an IV may also be at an increased risk of developing hyperglycemia, as the nutritional fluid contains a sugar solution to help restore electrolyte balance. The concentration of this fluid should be carefully monitored in patients who are ill or recovering from surgery or injury in order to prevent further spikes in blood sugar.


High blood sugar is associated with obesity since excess fat cells disrupt the balance of glucose and insulin. Excess fat cells called adipocytes release inflammatory proteins, such as interleukins and tumor necrosis factor, which increase the body’s resistance to insulin by activating processes that disrupt the body’s ability to produce and release insulin when blood sugar is high.

Excess fat cells also decrease the ability to remove glucose from the blood to be used for energy or stored as glycogen within skeletal muscles. With obesity, increased lipids, or fatty acid molecules, activate pathways that impair insulin signaling within muscles.



A family history of diabetes can increase your risk of developing hyperglycemia. While diabetes can be prevented through diet and lifestyle factors, impaired insulin sensitivity can run in families and may make you more prone to developing high blood sugar.

Pregnant women can also develop gestational diabetes, often between 24 and 28 weeks of pregnancy, due to hormonal changes that affect the way that glucose is metabolized in the body. The influence of pregnancy hormones can interfere with the ability of insulin to remove excess glucose from the blood, causing blood sugar to stay elevated.

Lifestyle Risk Factors 


Diet plays a significant role in the development of high blood sugar. Excess consumption of sugar- and carbohydrate-containing foods raise blood sugar levels after eating as the food is broken down into glucose molecules that enter the bloodstream.

In a healthy person, the presence of more glucose molecules in the blood signals the pancreas to release insulin, which helps uptake glucose from the blood and transports it to the muscles and liver to be used for energy and storage. As blood sugar decreases, the signals to the pancreas to release more insulin stop, and blood sugar levels should return to a stable baseline.

When levels of blood sugar continually become elevated with repeat and excessive sugar and carbohydrate consumption, the excess glucose in the bloodstream stimulates the pancreas to release a lot of insulin. Over time, the body stops responding to insulin due to chronic high blood sugar, causing insulin resistance and keeping blood sugar high.

Managing a healthy and balanced diet with proteins, fats, and fiber-rich foods while limiting sugar and processed and refined carbohydrates can help control blood sugar levels.

Excess alcohol consumption can also affect your blood sugar by interfering with your liver’s ability to regulate the production and release of glucose and negatively impact your body’s response to insulin.

Lack of Physical Activity

Lack of physical activity can increase your blood sugar, as skeletal muscles are a main part of the body that uses glucose for energy or stores extra glucose as glycogen for later use. With low levels of physical activity, the muscles become inactive and do not remove glucose efficiently from the blood.

Regular exercise can help lower blood sugar levels by increasing the need for muscles to remove glucose from the blood to use for energy.

A Word From Verywell

High blood sugar can result from a variety of causes, not just diabetes. You do not have to live with diabetes to develop hyperglycemia. Having high blood sugar can increase your risk of developing diabetes and related complications later on. 

A variety of factors can contribute to high blood sugar, and some of them like diet and exercise can help keep your blood glucose in check. Sometimes high blood sugar in people without diabetes could be due to prediabetes, which could lead to the development of diabetes. If you have high blood sugar often, it’s important to check with your healthcare provider and monitor it.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Kristen Gasnick, PT, DPT
Kristen Gasnick, PT, DPT, is a medical writer and a physical therapist at Holy Name Medical Center in New Jersey.