Section 13. Hormonal Disorders

Chapter 166. Hypoglycemia

Topic: Hypoglycemia

Hypoglycemia

Hypoglycemia is abnormally low levels of sugar (glucose) in the blood.

Normally, the body maintains the levels of sugar in the blood within a range of about 70 to 110 milligrams per deciliter (mg/dL) of blood. In hypoglycemia, the sugar levels in the blood become too low. In diabetes mellitus, the sugar levels in the blood become too high, a condition called hyperglycemia. Although diabetes is characterized by high levels of sugar in the blood, many people with diabetes periodically experience hypoglycemia. Hypoglycemia is uncommon among people without diabetes.

Low levels of sugar in the blood interfere with the function of many organ systems. The brain is particularly sensitive to low sugar levels, because sugar is the brain's major energy source. If the sugar levels in the blood fall far below their usual range, the brain responds by stimulating the adrenal glands to release epinephrine (adrenaline), the pancreas to release glucagon, and the pituitary gland to release growth hormone, all of which cause the liver to release sugar into the blood.

Causes

Drugs: Most cases of hypoglycemia occur in people with diabetes and are caused by the insulin or other drugs (for example, sulfonylureas) they take to lower the levels of sugar in their blood. People with diabetes sometimes call the hypoglycemia that can occur after taking insulin an "insulin reaction" or "being shaky." Insulin reactions are more common when intense efforts are made to keep the sugar levels in the blood as close to normal as possible. People who are losing weight or who develop kidney failure are more likely to have hypoglycemia. Older people are more susceptible than younger people to hypoglycemia resulting from sulfonylurea drugs.

If, after taking a dose of a drug for diabetes, a person eats less than usual or is more physically active than normal, the drug may lower the level of sugar in the blood too much. People with long-standing severe diabetes are particularly prone to hypoglycemia in these situations because they do not produce enough glucagon or epinephrine. The amounts of glucagon and epinephrine that are released are often too low to counteract a low level of sugar in the blood.

Many drugs other than those for diabetes, most notably pentamidine, used to treat a form of pneumonia that occurs most often as part of AIDS, and quinine, used to treat muscle cramps, can cause hypoglycemia.

An uncommon type of drug-related hypoglycemia sometimes occurs in people with Münchausen syndrome, who secretly take insulin or other drugs as part of their attention-seeking behavior (see Section 7, Chapter 99).

Fasting: In fasting hypoglycemia, the body is not able to maintain adequate levels of sugar in the blood after a period without food. Prolonged fasting and prolonged strenuous exercise, even after a period of fasting, are unlikely to cause hypoglycemia in otherwise healthy people, but they can do so occasionally.

There are several diseases or conditions that can cause fasting hypoglycemia. In people who drink heavily without eating, alcohol can block the release of stored sugar from the liver. In people with liver disease, such as viral hepatitis, cirrhosis, or cancer, the liver may not store sufficient sugar. Infants and children who have an abnormality of the enzyme systems that control sugar use also may have fasting hypoglycemia.

Reaction to Eating: Hypoglycemia can occur as a reaction to eating, usually carbohydrates. The body's response to food is excessive, so the body produces more insulin than is needed.

After certain types of stomach surgery, such as removal of part of the stomach, sugars are absorbed very quickly, stimulating excess insulin production. Problems with digestion of some sugars (fructose and galactose) and amino acids (leucine) may also cause reactive hypoglycemia. An uncommon form of reactive hypoglycemia can occur after drinking alcohol in combination with sugar (for example, a gin and tonic).

Other Causes: Some causes of hypoglycemia seem to have no specific relation to food, but fasting or vigorous exercise can trigger or worsen an episode of hypoglycemia. Rarely, a tumor in the pancreas can produce large amounts of insulin, leading to hypoglycemia. In some people, an autoimmune disorder lowers sugar levels in the blood by changing insulin secretion or by some other means. Disorders that lower hormone production by the pituitary and adrenal glands (most notably Addison's disease) can cause hypoglycemia. Certain severe diseases, such as kidney or heart failure, cancer, and shock, may also cause hypoglycemia, particularly in a person who is also being treated for diabetes.

Symptoms

The symptoms of hypoglycemia rarely develop until the level of sugar in the blood falls below 60 milligrams per deciliter of blood. Some people develop symptoms at slightly higher levels, especially when blood sugar levels fall quickly, and some do not develop symptoms until the sugar levels in their blood are much lower.

The body first responds to a fall in the level of sugar in the blood by releasing epinephrine (adrenaline) from the adrenal glands. Epinephrine stimulates the release of sugar 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 sugar 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. Prolonged hypoglycemia may permanently damage the brain. Symptoms can begin slowly or suddenly, progressing from mild discomfort to severe confusion or panic within minutes. On the infrequent occasions when people who have well-controlled diabetes develop hypoglycemia, awareness of the symptoms of hypoglycemia may be lost, and faintness or even coma may develop without any other warning.

In a person with an insulin-producing pancreatic tumor, symptoms are likely to occur early in the morning after an overnight fast, especially if the sugar 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 become more frequent and severe.

Diagnosis

In someone who is known to have diabetes, a doctor may suspect hypoglycemia when symptoms of hypoglycemia are described. The diagnosis may be confirmed when low sugar 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 sugar in the blood. A low sugar 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 sugar level in the blood and symptoms is demonstrated more than once. If symptoms are relieved as the sugar levels in the blood rise within a few minutes of ingesting sugar, the diagnosis is supported.

When the relationship between a nondiabetic person's symptoms and the level of sugar in the blood remains unclear, additional tests may be needed. Often, the next step is measurement of the sugar level in the blood after a night of fasting in a hospital or other closely supervised setting. More extensive tests may also be needed.

If the use of a drug such as pentamidine or quinine is thought to be the cause of hypoglycemia, the drug is stopped and blood sugar levels are measured to determine if they increase. If the cause remains unclear, other laboratory tests may be needed.

If an insulin-producing tumor is suspected, measurements of insulin levels in the blood during fasting (sometimes up to 72 hours) may be needed. If the insulin measurements reveal a tumor, the doctor will try to locate it before treatment.

Treatment

The symptoms of hypoglycemia are relieved within minutes of consuming sugar in any form, such as candy or glucose tablets, or of drinking 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. Both diabetic and nondiabetic people with hypoglycemia 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 sugar intravenously to prevent brain damage.

People who are known to be at risk of severe episodes of hypoglycemia may keep glucagon on hand for emergencies. Glucagon administration stimulates the liver to release large amounts of sugar. It is given by injection and generally restores blood sugar to an adequate level within 5 to 15 minutes.

Insulin-producing tumors should be removed surgically. However, because these tumors are small and difficult to locate, a specialist should perform the surgery. Before surgery, the person may be given a drug such as diazoxide to inhibit the tumor's insulin production. Sometimes more than one tumor is present, and if the surgeon does not find them all, a second operation may be necessary.

Nondiabetic people who are prone to hypoglycemia often can avoid episodes by eating frequent small meals rather than the usual three meals a day. People prone to hypoglycemia should carry or wear a medical identification bracelet or tag to inform health care professionals of their condition.