Home > Encyclopedia of Nursing & Allied Health > Diabetes Mellitus

Definition

Diabetes mellitus is a condition that occurs when either the pancreas does not produce enough insulin or the body's cells stop responding to the insulin that is produced. In either case, glucose in the blood cannot be absorbed or used by the cells of the body.

Description

Diabetes has been recognized as a disease since ancient times. Egyptian papyri described its symptoms in 1550 B.C., and Hindu physicians noted 500 years later that insects were drawn to the sugary urine of people afflicted with diabetes. The disease was first named in 230 B.C. by Apollonius of Memphis, who took it from the Greek diabainein (to pass through), a description of the unquenchable thirst and copious urine produced by diabetics. It was not until the latter part of the eighteenth century that the British physician John Rollo appended the Latin term mellitus (honey-sweet) to distinguish diabetes from other diseases that caused excessive urine production.

Diabetes mellitus is a chronic disease that causes serious health complications including renal failure, heart disease, stroke, blindness, and peripheral neuropathy with vascular insufficiency, putting patients at risk for gangrene and subsequent amputation of the extremities. Approximately 16 million Americans have diabetes; of these, it is estimated that around 5.4 million are undiagnosed. Diabetes afflicts 120 million people worldwide, with the World Health Organization predicting that the number will reach 300 million by 2025.

Physiology

Every cell in the human body requires fuel to function. The body's primary energy source is glucose, a simple sugar resulting from the digestion of foods containing carbohydrates. Glucose from the digested food circulates in the blood as a ready energy source for any cells that need it. Insulin is a protein hormone secreted into the blood by cells in the pancreas called islets of Langerhans. Insulin bonds to a receptor site on the outside of a cell, and acts like a key to open a doorway into the cell through which glucose can enter. The liver may convert excess glucose to concentrated energy sources like glycogen or fatty acids, which are stored for later use. If there is insufficient insulin production, or when the doorway no longer recognizes the insulin key, glucose stays in the blood rather than entering the cells.

As the level of glucose in the blood rises, a condition called hyperglycemia results. The body will try to dilute this high blood glucose level by drawing water out of the cells, pumping it into the bloodstream, and excreting it in urine. It is not unusual for those with undiagnosed diabetes to complain of constant thirst, to drink large quantities of fluids, and to urinate frequently as their bodies attempt to get rid of the extra glucose.

At the same time that the body is attempting to rid itself of glucose in the blood, its cells are starving for glucose and sends signals to eat more food, giving patients tremendous appetites. To provide energy for the starving cells, the body also tries to convert fats and proteins into glucose. Breaking down these substances causes acid compounds called ketones to form in the blood and to be excreted in the urine. As ketones build up in the blood, a condition called ketoacidosis can occur. If left untreated, this condition can be life threatening, eventually leading to coma and death.

Types of diabetes mellitus

Type 1 diabetes, sometimes called juvenile diabetes, commonly begins in childhood or adolescence. It occurs more frequently in populations descended from northern European countries than in those from southern Europe, the Middle East, or Asia. This form of diabetes is also called insulin-dependent diabetes because people who develop it need to have insulin injections at least once a day. In this form of diabetes, the body produces little or no insulin. Its onset is sudden, and it usually–but not always—occurs in people under 30.

Brittle diabetics are a subgroup of type 1 in which patients have frequent and rapid blood sugar level swings, alternating between hyper-and hypoglycemia. These patients may need several injections of different types of insulin taken at specific times during the day to maintain a blood glucose level within a fairly normal range.

The more common form of diabetes is type 2, sometimes called age-onset or adult-onset diabetes. It accounts for more than 90% of all diabetes in the United States. This form occurs most often in people who are over 50, as well as those who are overweight and sedentary; it is also more common in people of Native American, Hispanic, and African-American descent. People who have migrated to Western cultures from East India, Japan, and Australian Aboriginal cultures are also more likely to develop type 2 diabetes than those who remain in their native countries.

Type 2, also called noninsulin-dependent diabetes, is considered a milder form of diabetes because of its gradual onset (sometimes developing over the course of several years) and because it can often be controlled with diet and oral medication. The consequences of uncontrolled and untreated type 2 diabetes, however, are as serious as those caused by type 1. Many people with type 2 diabetes are able to control their blood glucose with diet and oral medications, but for those who cannot, insulin injections may be necessary. In recent years, an alarming trend was being noted in Western culture, particularly in the United States: a tendency for children, teenagers, and young adults, particularly those who are obese, to develop this type of diabetes.

Another type of diabetes is gestational diabetes, which can develop during pregnancy and generally resolves after the delivery of the baby. This diabetic condition develops during the second or third trimester in approximately 2% of pregnancies. The condition is normally treated by diet, however, insulin injections may be required for periodic exacerbation control. Women who develop diabetes during pregnancy are at higher risk for developing type 2 diabetes within five to 10 years.

Diabetes may also develop as a result of or in concert with pancreatic disease, alcoholism, malnutrition, or other severe illnesses that tax the body's immune system.

Causes and symptoms

The causes of diabetes mellitus are unclear, however, there appear to be both hereditary and environmental factors involved. Research has shown that some people who develop diabetes have common genetic markers. In type 1 diabetes, the immune system is probably triggered by a virus or other microorganism that destroys the cells in the pancreas that produce insulin.

Type 2 diabetes is characterized by the insulin resistance syndrome, in which peripheral adipose and muscle cells fail to respond appropriately to circulating insulin, which the pancreas produces in response to food loads. Research has now shown that the insulin resistance syndrome is closely associated with dyslipidemia, an imbalance in the ratio of total cholesterol to the cholesterol fractions of either low-density lipoproteins (bad cholesterol) or to high-density lipoproteins (good cholesterol). Untreated or inadequately treated dyslipidemia leads to atherosclerosis and eventually to the microvascular complications mentioned above. Patients with type 2 diabetes and dyslipidemia are often treated with one of the drugs from the group known as statins, in addition to oral antidiabetic agents.

Age, obesity, and family history may all play a role in the development of type 2 diabetes. Symptoms may begin so gradually that a person may not be aware of them. Early signs are fatigue, extreme thirst, and frequent urination. Other symptoms may include sudden weight loss, slow wound healing, urinary tract infections, or blurred vision. It is not unusual for type 2 diabetes to be detected while a patient is seeing a doctor for another health concern that is actually being caused by the as-yetundiagnosed diabetes.

Individuals who are at high risk of developing type 2 diabetes mellitus include those who:

• Are obese (more than 20% above their ideal body weight).
• Have a primary relative (immediate family member) with diabetes mellitus.
• Belong to a high-risk ethnic population (African American, Native American, Hispanic, or Native Hawaiian).
• Have been diagnosed with gestational diabetes or have delivered a baby weighing more than 9 lbs (4 kg).
• Have been diagnosed with transient diabetes at the time of a moderate to severe systemic infection (like protracted pneumonia).
• Have high blood pressure (140/90 mm Hg or above).
• Have a high-density lipoprotein cholesterol level less than or equal to 35 mg/dL and/or a triglyceride level greater than or equal to 250 mg/dL.
• Have had impaired glucose tolerance or impaired fasting glucose on previous testing.

Several common medications can impair the body's use of insulin, causing a condition known as secondary diabetes. These medications include treatments for high blood pressure (furosemide, clonidine, and thiazide diuretics), drugs with hormonal activity (oral contraceptives, thyroid hormone, progestins, and systemic gluococorticoids), and the anti-inflammation drug indomethacin. Several drugs used to treat mood disorders can also impair glucose absorption. These drugs include haloperidol, lithium carbonate, phenothiazines, tricyclic antidepressants, and adrenergic agonists. Other medications that can cause diabetes symptoms include isoniazid, nicotinic acid, cimetidine, and heparin.

Symptoms

Symptoms of diabetes can develop suddenly (over days or weeks) in previously healthy children or adolescents, or can develop gradually (over several years) in overweight adults past the age of 40. The classic symptoms include fatigue, frequent urination, excessive thirst, excessive hunger, tingling of hands and feet, pruritus, and weight loss. In sudden-onset diabetes, some patients may have a "fruity" odor to their breath.

Ketoacidosis, a condition that results from starvation or uncontrolled diabetes, is common in patients with type 1 diabetes. Its symptoms include abdominal pain, vomiting, tachypnea, and extreme fatigue or lethargy. Patients with ketoacidosis will also have a characteristically sweet, fruity breath odor. Left untreated, this condition may lead to coma and death.

With type 2 diabetes, the condition may not become evident until the patient presents for medical treatment for some other condition. A patient may have heart disease, chronic infections of the gums and urinary tract, blurred vision, numbness in the feet and legs, and slowly healing wounds. Women may experience genital itching.

Diagnosis

Urine tests

Diabetes is suspected based on symptoms, but many of its symptoms may also suggest other diseases. Urine tests can begin the winnowing process that leads to a definitive diagnosis. Urine tests can detect ketones and protein in the urine; they can also show urine "spill," the renal threshold at which the kidneys will spill excess blood sugar into the urine. They can help assess how adequately the kidneys are functioning, and are used to monitor the disease once the patient is compliant with the recommended diet, oral medications, or insulin.

Blood tests

Although urine tests can confirm an initial suspicion of diabetes, specific blood tests are often required to make the differential diagnosis. One such diagnostic tool is the fasting glucose test. Blood is drawn via a venipuncture after a period of at least eight hours of fasting, usually in the morning prior to breakfast. The red blood cells are separated from the sample and the amount of glucose is measured in the remaining plasma. A plasma level of 7.8 mmol/L (200 mg/L) or greater can indicate diabetes. The fasting glucose test is usually repeated on another day to confirm the results. A postprandial glucose test involves taking blood one to two hours after the patient has eaten a meal.

A glucose tolerance involves blood and urine sampling over a three-or five-hour period after a patient drinks a specially prepared syrup of glucose and other sugars. During the test the patient drinks no other fluids. When patients are healthy, the blood glucose level rises immediately after the drink and then decreases gradually as insulin is used by the body to metabolize the glucose. In patients with diabetes, the serum glucose rises and stays elevated after drinking the sweetened liquid. A plasma glucose level of 11.1mmol/L (200 mg/dL) or higher two hours after drinking the syrup and at one other point during the two-hour test period confirms the diagnosis of diabetes. During this time, the urine is tested for glucose spill.

A diagnosis of diabetes is confirmed if there are symptoms of diabetes and a blood glucose level of at least 11.1 mmol/L, a fasting plasma glucose level of at least 7 mmol/L, or a two-hour plasma glucose level of at least 11.1 mmol/L during an oral glucose tolerance test.

Monitoring glucose levels

The blood test that gives the best indication of average blood glucose levels over time is the hemoglobin A1C (HbA1C) test. It measures the percentage of hemoglobin A that has become glycosylated (coated with glucose) during the past three months. (Red blood cells have a life span of about 100 days; after that they are recycled by the bone marrow.) A normal reading for healthy individuals is about of 4–6% glycosylated HbA1C. Diabetics whose disease is well controlled will read 7% or lower. A reading of 8% or higher indicates the need for a change in treatment or better dietary compliance; these patients are also at increased risk for such complications as eye disease, kidney disease, and nerve damage. The HbA1C test should be performed at least twice a year to be sure that blood glucose levels stay within safe and healthy levels.

Home blood glucose monitoring kits are available so patients with diabetes can monitor their daily glucose readings. For decades, a small needle or lancet was used to prick the finger and a drop of blood was collected and analyzed by a monitoring device. Modern blood monitoring devices, however, are strapped on like a wrist watch; no finger sticks are required. This is especially helpful for patients who need to test their blood glucose levels several times during the day.

Treatment

There is no cure for diabetes; it can, however, be controlled so that patients can live a relatively normal life. Treatment focuses on two goals: keeping blood glucose readings within a normal range (140 mg/dL, the standard accepted by the American Diabetes Association) and preventing the development of long-term complications. Careful monitoring of diet, exercise, and blood glucose levels are important, affecting the need for insulin replacement as well as the dose of oral antidiabetic agents. Lack of consistent control leads to complications of the disease.

Dietary changes

Diet and moderate exercise are the first treatments implemented in diabetes. For many type 2 diabetics, weight loss may be an especially important part of treatment. A well balanced, nutritious diet provides approximately 50% to 60% of calories from carbohydrates, around 10% to 20% from protein, and less than 30% of calories from fat. The number of calories required by an individual depends on their age, weight, and activity level. Calorie intake also needs to be distributed over the course of the entire day so that surges of glucose entering the blood are kept to a minimum. The timing of snacks must also correspond to the timing and type of insulin being used.

Counting the calories in different foods can be complicated, so patients are usually advised to consult a nutritionist, who will set up an individualized, easily managed diet for each patient. Both the American Diabetes Association and the American Dietetic Association recommend diets based on the use of food-exchange lists. Each food-exchange unit contains a known amount of calories in the form of protein, fat, or carbohydrate. A patient's diet plan will allow a certain number of exchanges from each food category (meat or protein, fruits, breads and starches, vegetables, and fats) to be eaten at mealtimes and as snacks. Patients can choose which foods they eat as long as they stick with the number of exchanges prescribed and adhere to their schedule if they take a combination of insulin types. The food exchange system, along with an exercise program, can help patients lose excess weight and improve their overall health. This may be especially important for type 2 diabetics.

Oral medications

A variety of oral medications are available to help lower blood glucose in type 2 diabetics. They act in a variety ways to control postprandial (after meal) glucose levels; the particular medication or combination of drugs chosen will be based largely on the individual patient profile. Some oral medications stimulate the pancreatic beta cells to produce additional insulin. Others change the way receptors on peripheral adipose (fat) and muscle cells receive the insulin and act on it, and still others block the intestinal absorption of food byproducts that would increase blood glucose levels.

All drugs have side effects that may make them inappropriate for particular patients. For example, some medications may stimulate weight gain or cause stomach irritation, so they may not be the best treatment for individuals who are already overweight or who have stomach ulcers. While these medications are an important aspect of treatment for type 2 diabetes, they are not a substitute for an appropriate diet and exercise. Oral medications are not effective for type 1 diabetes, in which the patient produces little or no insulin.

Insulin

Patients with type 1 diabetes need daily injections of insulin to help their bodies utilize glucose. The amount and type of insulin required depends on the individual patient's height, weight, age, food intake (quantity and timing), and activity level. Some patients with type 2 diabetes may need to use insulin injections if their diabetes cannot be controlled with diet, exercise, and oral medication. Injections are given subcutaneously, using a small needle and syringe. Injection sites can be anywhere on the body where there is adequate subcutaneous tissue, including the upper arm, abdomen, hips, or upper thigh.

Purified human insulin is most commonly used, however, insulin from beef and pork sources is also available. Insulin may be given as an injection of a single dose of one type of insulin once a day. Different types of insulin (short-acting rapid-onset, slow-onset long-acting) can be mixed and given in one dose or split into two or more doses during the day. Patients that require multiple injections over the course of a day may be able to use an insulin pump that administers small doses of insulin on demand. The small battery-operated pump is worn outside the body and is connected to a tube that is inserted into the abdomen. Pumps can be programmed to inject small doses of insulin at various times during the day, or the patient may be able to adjust the insulin doses to coincide with glucometer readings, meals, and exercise. There are also multiple-dose insulin injection devices available that are commonly referred to as insulin pens. They are designed to hold a cartridge containing several days' worth of insulin dosages.

Regular human insulin is fast-acting and begins to work within 15–30 minutes; its peak glucose-lowering effect occurs about two hours later and its effects last approximately 4–6 hours. Neutral protamine Hagedorn (NPH) and Lente insulin are intermediate-acting insulins that start to work within 4–8 hours, and last 18–26 hours. Ultralente is a long-acting form of insulin that starts to work within four to eight hours and lasts 28 to 36 hours. Many diabetics combine a long-or intermediate acting insulin with a short-acting one to provide the proper insulin peak at mealtimes. Premixed insulins are available in standard doses. Newer forms of insulin are under investigation.

Although the goal of most diabetes treatment is to lower blood glucose levels, hypoglycemia, or low blood glucose, can be caused by too much insulin, too little food, alcohol consumption, or increased exercise. A patient with symptoms of hypoglycemia may be hungry, irritable, confused, and tired. The patient may be diaphoretic (sweating profusely), pale, and shaky. Left untreated, the patient can lose consciousness or have a seizure soon after these symptoms appear. This condition, called an insulin reaction or insulin shock, should be treated by giving the conscious patient something with readily available sugar to eat or drink like orange juice, hard candy, or sugar cubes. If the patient has declined into unconsciousness, do not try to feed them. This is a critical condition and always requires emergency intravenous therapy.

Surgery

Transplantation of healthy pancreatic tissue into a diabetic patient can be successful. However, it is not clear if the potential benefits outweigh the risks of the surgery and drug therapy required.

Alternative therapies

Since uncontrolled diabetes can be life-threatening if not properly managed, patients should be instructed to not attempt treatments without medical supervision. Patients interested in alternative and herbal remedies should be instructed about the possible benefits, but cautioned to consult with a health care professional before they try them. Some alternative therapies may interact negatively with some of the oral antidiabetic agents or other drugs, such as antihypertensives or anticoagulants.

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KEY TERMS

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Diabetic peripheral neuropathy—Condition in which the sensitivity of nerves to pain, temperature, and pressure is dulled, particularly in the legs and feet.

Diabetic retinopathy—A condition in which the tiny blood vessels to the retina are damaged, leading to blurred vision, sudden blindness, or black spots, lines, or flashing light in the field of vision.

Hemoglobin A—Normal hemoglobin found in the blood of an adult.

Hemoglobin A1C—One of three fractions of hemoglobin A; the other two are HBA1a and HbA1b. Because HbA1c can become glycosylated, it is an important measure of blood glucose over the past three months.

Hyperglycemia—Abnormally high levels of blood glucose.

Hypoglycemia—Abnormally low levels of blood glucose.

Ketoacidosis—Condition that results in untreated diabetes from the body's attempt to burn fat for fuel when carbohydrates cannot be utilized. Ketones, the byproduct of fat metabolism, enter the bloodstream and make the blood more acidic than the body's tissues.

Pruritus—Itching.

Tachypnea—Rapid breathing.

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For patients who are willing to consult with their physician, alternative options may include:

• Fenugreek has been shown in some studies to reduce blood insulin and glucose levels while also lowering cholesterol.
• Bilberry may lower blood glucose levels, as well as help to maintain healthy blood vessels.
• Garlic may lower blood sugar and cholesterol levels.
• Cayenne pepper may help relieve the pain of diabetic neuropathy.

Any therapy that lowers stress levels may also be useful in treating diabetes by helping to reduce insulin requirements. Among the alternative treatments that aim to lower stress are hypnotherapy, biofeedback, and meditation.

Prognosis

Uncontrolled diabetes is a leading cause of blindness, end-stage renal disease, and peripheral vascular insufficiency, which leads to limb amputations. It also doubles the risks of heart disease and increases the risk of stroke. Eye problems including cataracts, glaucoma, and diabetic retinopathy are also more common in diabetics.

Diabetic peripheral neuropathy is a condition where nerve endings, particularly in the legs and feet, become less sensitive. Diabetic foot ulcers are a particular problem since the patient does not feel the pain of a blister, callous, or other minor injury. Poor blood circulation in the legs and feet contribute to delayed wound healing. The inability to sense pain along with the complications of delayed wound healing can cause minor injuries, blisters, or calluses to become infected and difficult to treat. In cases of severe infection, the infected tissue begins to break down and rot away. The severe infection may further exacerbate diabetes and increase blood glucose levels, perpetuating the problem. In the most serious infection cases, toes, feet, or legs may need to be amputated.

Diabetes can also affect the kidneys, a condition called diabetic nephropathy. This usually means that soft kidney tissue hardens and thickens, a process called sclerosis; this is especially true for the glomerulus (kidney membrane), which filters protein and other waste products from the blood. The ADA estimates that 35–45% of type 1 patients and 20–30% of type 2 patients have damaged kidneys. Because the symptoms of nephropathy may not appear until 80% of kidney function is gone, periodic tests of kidney function are especially important for patients with diabetes. Once renal function drops to 10–15%, kidney dialysis or a kidney transplant become necessary.

The risk of heart disease for patients with diabetes is two to four times higher than that of the general population. Death from heart disease is also two to four time higher in diabetics, as is the risk of stroke. These statistics hold for people with both type 1 and type 2 diabetes. The risk of cardiovascular disease increases with age, obesity, smoking, poor blood glucose control, and family history of heart disease.

Health care team roles

All members of the health care team may come into contact with diabetic patients. The nurse plays a particularly important role in teaching patients the skills necessary to manage this complex disease, and educating them about the effects of their medications.

Prevention

Research continues on ways to prevent diabetes and to detect those at risk for developing the disease. While the onset of type 1 diabetes is unpredictable, the risks for developing type 2 diabetes can be reduced by maintaining a healthy weight and exercising regularly. The physical and emotional stresses of surgery, illness (especially systemic infection), pregnancy, and alcoholism can all increase the risks for diabetes, so maintaining a healthy lifestyle is critical to preventing the onset of type 2 diabetes and further complications. Research is in progress to determine the usefulness of placing high-risk patients on metformin (Glucophage; an oral antidiabetic drug used to treat type 2 diabetes) prophylactically in an effort to delay or prevent the onset of type 2 diabetes.

Deanna M. Swartout-Corbeil, R.N.