Normally, the body maintains the level of blood sugar within a rather narrow range (about 70 to 110 milligrams per deciliter of blood). In diabetes, the blood sugar levels become too high; in hypoglycaemia, the blood sugar levels become too low. Low blood sugar causes many organ systems in the body to malfunction. The brain is particularly sensitive to low blood sugar levels, because glucose is the brain's major energy source. The brain responds to low blood sugar levels and, through the nervous system, stimulates the adrenal glands to release epinephrine (adrenaline). This stimulates the liver to release sugar to adjust the level in the blood. If the level falls too low, the brain's function may be impaired.
Hypoglycemia has several different causes: excessive secretion of insulin from the pancreas, too high a dose of insulin or other medication given to a diabetic person to lower the blood sugar levels, an abnormality in the pituitary or adrenal glands, or an abnormality in the liver's storage of carbohydrate or production of glucose.
In general, hypoglycaemia can be categorized as drug-related or non-drug-related. Most cases of hypoglycaemia occur in diabetics and are drug-related. Non-drug-related hypoglycaemia can be further divided into fasting hypoglycaemia, in which hypoglycaemia occurs after fasting, and reactive hypoglycaemia, in which hypoglycaemia oc-curs as a reaction to eating, usually of carbohydrates.
Most often, hypoglycaemia is caused by insulin or other drugs (sulphonylureas) given to people with diabetes to lower the blood sugar levels. If the dose is too high for the amount of food eaten, the drug may lower the blood sugar levels too much. People with long-standing severe diabetes are particularly prone to severe hypoglycemia. This happens because their pancreatic islet cells don't produce glucagon normally and their adrenal glands don't produce epinephrine normally-the major immediate mechanisms by which the body counteracts a low blood sugar level. Many drugs other than those for diabetes, most notably pentamidine used to treat a form of AIDS-related pneumonia, can cause hypoglycaemia.
Hypoglycaemia is sometimes seen in people with psychologic disturbances who surreptitiously administer insulin or hypoglycemic drugs to themselves. The people likely to do this are usually those who have access to the drugs, such as health care workers or relatives of diabetics.
Alcohol consumption, usually in people who drink heavily without eating for a long time (which depletes carbohydrates stored in the liver), can produce hypoglycaemia severe enough to cause stupor. Hypoglycaemia-induced stupor can even occur in a person whose blood alcohol level is below that legally allowed for driving. Police and emergency department personnel may not realize that a stuporous person whose breath smells of alcohol is hypoglycaemic rather than just inebriated.
Prolonged strenuous exercise rarely induces hypoglycaemia in otherwise healthy people. Prolonged fasting causes hypoglycaemia only if a person has another disease, especially a disease of the pituitary or adrenal glands, or consumes large amounts of alcohol. The liver's carbohydrate stores may fall so low that the body can't maintain adequate blood sugar levels. In some people with a liver abnormality, just a few hours of fasting may cause hypoglycaemia. Infants and children with an abnormality in any of the liver enzyme systems that metabolize sugars may develop hypoglycaemia between meals.
Some people who have undergone certain types of stomach surgery develop hypoglycaemia between meals (alimentary hypoglycemia, a type of reactive hypoglycaemia). Hypoglycaemia occurs because sugars are absorbed very quickly, stimulating excessive insulin production. The high level of insulin causes a rapid fall in the blood sugar level. Rarely, alimentary hypoglycaemia occurs in people who haven't had surgery, in whom the condition is called idiopathic alimentary hypoglycaemia.
In the past, doctors tended to diagnose reactive hypoglycaemia in people who had symptoms resembling those of hypoglycaemia 2 to 4 hours after a meal or to diagnose people with vague symptoms (mainly fatigue) as having hypoglycaemia. However, measurement of blood sugar levels during an episode of symptoms doesn't reveal true hypoglycaemia. Attempts have been made to reproduce reactive hypoglycaemia with an oral glucose tolerance test, but this test doesn't accurately reflect what happens after a normal meal.
A type of reactive hypoglycaemia that occurs in infants and children is caused by foods that contain the sugars fructose and galactose or the amino acid leucine. Fructose and galactose prevent the release of glucose from the liver; leucine stimulates overproduction of insulin from the pancreas.
In either case, the result is a low blood sugar level some time after eating foods containing these nutrients. In adults, the ingestion of alcohol in combination with sugar, for example, as a gin and tonic, may precipitate reactive hypoglycaemia.
Excessive insulin production also can cause hypoglycaemia. Excessive production may result from a tumor of the pancreas' insulin-producing cells (an insulinoma) or, rarely, from a generalized proliferation of these cells. Infrequently, a tumor outside the pancreas causes hypoglycaemia by producing an insulinlike hormone.
A rare cause of hypoglycaemia is an autoimmune disease in which the body produces antibodies to insulin. The levels of insulin in the blood fluctuate abnormally as the pancreas produces excessive insulin to cope with the antibodies. This condition may occur in people with or without diabetes.
Hypoglycaemia can also result from kidney or heart failure, cancer, malnutrition, abnormal pituitary or adrenal function, shock, and severe infection. Extensive liver disease for example from viral hepatitis, cirrhosis, or cancer may also produce hypoglycemia.
The body first responds to a fall in blood sugar levels by releasing epinephrine (adrenaline) from the adrenal glands and certain nerve endings. Epinephrine stimulates the release of sugar from body stores but also causes symptoms similar to those of an anxiety attack: sweating, nervousness, quivering, faintness, palpitations, and sometimes hunger. More severe hypoglycaemia reduces the glucose supply to the brain, causing dizziness, confusion, fatigue, weakness, headaches, inappropriate behavior that can be mistaken for drunkenness, inability to concentrate, vision abnormalities, epilepsylike seizures, and coma.
Prolonged hypoglycaemia may permanently damage the brain. Both the anxietylike symptoms and impairment of brain function can begin slowly or suddenly, progressing from mild discomfort to severe confusion or panic within minutes. People who take insulin or oral hypoglycaemic drugs for diabetes are most commonly affected.
In a person with an insulin-producing pancreatic tumour, symptoms are likely to occur early in the morning after an overnight fast, especially if the blood sugar stores are further depleted by exercise before breakfast. At first, people with a tumour usually have only occasional episodes of hypoglycaemia, but over months or years, episodes become more frequent and severe.
Doctors measure the blood sugar and then insulin levels when a nondiabetic and otherwise healthy person develops anxiety, drunkenlike behavior, or the other symptoms of impaired brain function described above. The symptoms of hypoglycaemia rarely develop until the blood sugar level falls below 50 milligrams per deciliter of blood, although occasionally people develop symptoms at slightly higher levels, and some don't develop symptoms until their levels are much lower. Low blood sugar levels along with the symptoms of hypoglycaemia confirm the diagnosis. If symptoms are relieved as the blood sugar level rises within a few minutes of ingesting sugar, the diagnosis is supported.
A doctor tests a person's blood sugar in the doctor's office. Blood sugar can be tested at home, using a drop of blood obtained by pricking the finger at the time symptoms occur and a device to monitor blood sugar levels, but home monitoring of blood sugar is recommended only for diabetics. The oral glucose tolerance test, which is commonly used to help diagnose diabetes, is rarely used for diagnosing hypoglycaemia because results are often misleading.
A doctor can almost always find the cause of hypoglycaemia. The person's medical history, a physical examination, and simple laboratory tests are usually all that are needed to determine the cause. However, a few people may need to be hospitalized for more extensive testing. If the doctor suspects autoimmune hypoglycaemia, the blood is tested for antibodies to insulin.
Measurements of insulin levels in the blood during fasting (sometimes up to 72 hours) may be needed to determine whether the person has an insulin-secreting tumor. Ideally, a tumour should be located before surgery. However, although some insulin-secreting tumours of the pancreas are visible on a computed tomography (CT) scan, magnetic resonance imaging (MRI) scan, or ultra-sound imaging, tumours are usually so small that they can't be detected with these imaging devices. Frequently, exploratory surgery is needed to detect an insulin-secreting tumor.
The symptoms of hypoglycaemia are relieved within minutes of consuming sugar in any form, such as candy or glucose tablets, or of drinking a glass of fruit juice, a glass of water with several tablespoons of sugar, or a glass of milk (which contains lactose, a type of sugar). People with recurring episodes of hypoglycaemia, especially diabetics, 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 hypoglycaemia may benefit from consuming sugar followed by a food that provides longer-lasting carbohydrates (such as bread or crackers). When hypoglycaemia is severe or prolonged and taking sugar by mouth isn't possible, doctors give glucose intravenously to prevent serious brain damage.
People who are known to be at risk for severe episodes of hypoglycaemia may keep glucagon on hand for emergencies. Glucagon is a protein hormone secreted by the islet cells of the pancreas, which stimulates the liver to produce large amounts of glucose from its carbohydrate stores. It is given by injection and generally restores blood sugar within 5 to 15 minutes.
Insulin-secreting tumours should be removed surgically. However, since they are very small and difficult to locate, the surgery should be performed by a specialist experienced in dealing with this problem. Before surgery, the person may need a drug such as diazoxide to inhibit the tumour's insulin secretion. Sometimes more than one tumour is present, and if the surgeon doesn't find them all, a second operation may be necessary.
Nondiabetics who are prone to hypoglycaemia often can avoid episodes by eating frequent small meals rather than the usual three meals a day. People prone to hypoglycaemia should carry identification or a Medic Alert bracelet to inform emergency medical personnel of their condition.
STEFAN, S.F. MD
The author is a professor Emeritas of Michigan University.
Similar of Hypoglycaemia