Hypoglycemia is abnormally low levels of sugar (glucose) in the blood.
Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include other medications, critical illness or organ failure, a reaction to carbohydrates (in susceptible people), an insulin-producing tumor in the pancreas, and some types of bariatric (weight loss) surgery.
A fall in blood glucose causes symptoms such as hunger, sweating, shakiness, fatigue, weakness, and inability to think clearly, whereas severe hypoglycemia causes symptoms such as confusion, seizures, and coma.
The diagnosis is based on finding low glucose levels in the blood while the person is experiencing symptoms.
Symptoms of hypoglycemia are treated by consuming sugar in any form.
Doses of medications that cause hypoglycemia may need to be decreased.
(See also Diabetes Mellitus.)
Normally, the body maintains the level of glucose in the blood within a range of about 70 to 110 milligrams per deciliter (mg/dL), or 3.9 to 6.1 millimoles per liter (mmol/L) of blood. In hypoglycemia, the glucose level becomes too low. Although diabetes mellitus, a disorder involving blood glucose levels, is characterized by high levels of glucose in the blood (hyperglycemia), many people with diabetes periodically experience hypoglycemia due to side effects of diabetes treatment. Hypoglycemia is uncommon among people without diabetes.
Very low levels of glucose in the blood may interfere with the function of certain organ systems. The brain is particularly sensitive to low glucose levels because sugar is the brain's major energy source. To prevent glucose levels in the blood from falling too far below their usual range, the brain responds by stimulating the
Adrenal glands to release epinephrine (adrenaline)
Adrenal glands to release cortisol
Pancreas to release glucagon
Pituitary gland to release growth hormone
All of these hormones cause the liver to release glucose into the blood, but sometimes these hormones do not raise the blood glucose level enough to overcome the hypoglycemia. If the blood glucose level remains too low, the brain will get insufficient fuel, resulting in confusion, seizures, or loss of consciousness.
Causes of Hypoglycemia
Medications
Most cases of hypoglycemia occur in people with diabetes and are caused by insulinMedication Treatment of Diabetes Mellitus: Oral Antihyperglycemic Medicationschronic kidney disease are more likely to have hypoglycemia. Older adults are more susceptible than younger people to hypoglycemia resulting from sulfonylurea medications.
If, after taking a dose of a medication for diabetes, a person eats less than usual or is more physically active than normal, the medication may lower the level of glucose in the blood too much. People with type 1 diabetes or people with long-standing type 2 diabetes (at least 10 years) are more prone to hypoglycemia in these situations because they may not produce enough glucagon or epinephrine to counteract a low level of glucose in the blood.
An uncommon type of medication-related hypoglycemia sometimes occurs in people who secretly take insulin or other medications that treat diabetes as part of a psychologic disorder such as factitious disorder imposed on self (previously called Munchausen syndrome).
Fasting hypoglycemia
In otherwise healthy people, prolonged fasting (even up to several days) and prolonged strenuous exercise (even after a period of fasting) are unlikely to cause hypoglycemia.
However, there are several diseases or conditions in which the body fails to maintain adequate levels of glucose in the blood after a period without food (fasting hypoglycemia). In people who drink heavily without eating, alcohol can block the formation of glucose in the liver. In people with advanced liver disease, such as viral hepatitis, cirrhosis, or cancer, the liver may not be able to store and produce sufficient glucose. Infants and children who have an abnormality of the enzyme systems that control glucose use (such as a glycogen storage disease) also may have fasting hypoglycemia.
A rare cause of fasting hypoglycemia is an insulinoma, which is an insulin-producing tumor in the pancreas. Disorders that lower hormone production by the pituitary and adrenal glands (most notably Addison disease) can cause hypoglycemia. Other diseases, such as chronic kidney disease, heart failure, cancer, and sepsis, may also cause hypoglycemia, especially in critically ill people.
Reaction to eating
Hypoglycemia can occur after a person eats a meal containing a large amount of carbohydrates (reactive hypoglycemia) if the body produces more insulin than is needed. However, this type of reaction is rare. In some cases, people with normal blood glucose levels experience symptoms that can be confused with hypoglycemia.
After certain types of bariatric surgery, such as gastric bypass surgery, sugars are absorbed very quickly, stimulating excess insulin production, which then may cause hypoglycemia.
Rare problems with metabolism of some sugars (fructose and galactose) and amino acids (leucine) may also cause hypoglycemia if an affected person eats foods containing those substances.
Symptoms of Hypoglycemia
Mild hypoglycemia: Sweating, nervousness, shaking, faintness, palpitations, and hunger
Severe hypoglycemia: Dizziness, fatigue, weakness, headaches, inability to concentrate, confusion, slurred speech, blurred vision, seizures, and coma
Hypoglycemia symptoms rarely develop until the level of glucose in the blood falls below 60 mg/dL (3.3 mmol/L). Some people develop symptoms at slightly higher levels, especially when blood glucose levels fall quickly, and some do not develop symptoms until the glucose levels in their blood are much lower.
The body first responds to a fall in the level of glucose in the blood by releasing epinephrine from the adrenal glands. Epinephrine is a hormone that stimulates the release of glucose from body stores but also causes symptoms similar to those of an anxiety attack: sweating, nervousness, shaking, faintness, palpitations, and hunger.
More severe hypoglycemia reduces the glucose supply to the brain, causing dizziness, fatigue, weakness, headaches, inability to concentrate, confusion, inappropriate behavior that can be mistaken for drunkenness, slurred speech, blurred vision, seizures, and coma. Severe and prolonged hypoglycemia may permanently damage the brain.
Symptoms can begin slowly or suddenly, progressing from mild discomfort to severe confusion or panic within minutes. Sometimes, people who have had diabetes for many years (especially if they have had frequent episodes of hypoglycemia) are no longer able to sense the early symptoms of hypoglycemia, and faintness or even coma may develop without any other warning.
In a person with an insulinoma, symptoms are likely to occur early in the morning after an overnight fast, especially if the glucose stores in the blood are further depleted by exercise before breakfast. At first, people with a tumor usually have only occasional episodes of hypoglycemia, but over months or years, episodes may become more frequent and severe.
Diagnosis of Hypoglycemia
Blood tests to measure glucose level
In someone who is known to have diabetes, a doctor may suspect hypoglycemia when symptoms are described. The diagnosis may be confirmed when low glucose levels in the blood are measured while the person is experiencing symptoms.
In an otherwise healthy person who does not have diabetes, a doctor is usually able to recognize hypoglycemia based on the symptoms, medical history, a physical examination, and simple tests.
Doctors first measure the level of glucose in the blood. A low glucose level in the blood found at the time a person is experiencing typical symptoms of hypoglycemia confirms the diagnosis in a person without diabetes, especially if the relationship between a low glucose level in the blood and symptoms is demonstrated more than once. If symptoms are relieved as the glucose levels in the blood rise within a few minutes of ingesting sugar, the diagnosis is supported.
When the relationship between a person's symptoms and the level of glucose in the blood remains unclear in a person who does not have diabetes, additional tests may be needed. Often, the next step is measurement of the glucose level in the blood after fasting in a hospital or other closely supervised setting. More extensive tests may also be needed.
If an insulinoma is suspected, measurements of insulin levels in the blood during fasting (sometimes up to 72 hours) may be needed. If the insulin levels are high and suggest a tumor, the doctor will try to locate it before treatment.
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Treatment of Hypoglycemia
Consuming sugar to raise the level of glucose in the blood
Changing medication doses
Eating several small meals during the day
Sometimes surgery to remove a tumor
People prone to hypoglycemia should carry or wear medical identification to inform health care professionals of their condition.
Immediate treatment of hypoglycemia
The symptoms of hypoglycemia are relieved within minutes of consuming sugar in any form, such as candy, glucose tablets, or a sweet drink, such as a glass of fruit juice. People with recurring episodes of hypoglycemia, especially those with diabetes, often prefer to carry glucose tablets because the tablets take effect quickly and provide a consistent amount of sugar. These people may benefit from consuming sugar followed by a food that provides longer-lasting carbohydrates (such as bread or crackers). When hypoglycemia is severe or prolonged and taking sugar by mouth is not possible, doctors quickly give glucose intravenously to prevent brain damage.
Glucagon administration stimulates the liver to release large amounts of glucose. It is given by injection or by a nasal inhaler and generally restores blood glucose to an adequate level within 5 to 15 minutes. Glucagon kits are easy to use, and family members or trusted others can be trained to administer the glucagon.
Treatment of the cause of hypoglycemia
If a medication is causing hypoglycemia, the dose is adjusted or the medication is changed.
People who do not have diabetes but are prone to hypoglycemia often can avoid episodes by eating frequent small meals rather than the usual three meals a day.
