Cystic Fibrosis Test
The sweat chloride test is a common and simple test used to evaluate a patient who is suspected of having cystic fibrosis (CF), the most common lethal genetic disease affecting Caucasians.
*Cystic fibrosis facts medical author: Melissa Conrad Stöppler, MD
The sweat chloride test is a common and simple test used to evaluate a patient who is suspected of having cystic fibrosis (CF), the most common lethal genetic disease affecting Caucasians.
Cystic fibrosis is an inherited disease characterized by the buildup of thick, sticky mucus that can damage many of the body's organs. The disorder's most common signs and symptoms include progressive damage to the respiratory system and chronic digestive system problems. The features of the disorder and their severity varies among affected individuals.
Mucus is a slippery substance that lubricates and protects the linings of the airways, digestive system, reproductive system, and other organs and tissues. In people with cystic fibrosis, the body produces mucus that is abnormally thick and sticky. This abnormal mucus can clog the airways, leading to severe problems with breathing and bacterial infections in the lungs. These infections cause chronic coughing, wheezing, and inflammation. Over time, mucus buildup and infections result in permanent lung damage, including the formation of scar tissue (fibrosis) and cysts in the lungs.
Most people with cystic fibrosis also have digestive problems. Some affected babies have meconium ileus, a blockage of the intestine that occurs shortly after birth. Other digestive problems result from a buildup of thick, sticky mucus in the pancreas. The pancreas is an organ that produces insulin (a hormone that helps control blood sugar levels). It also makes enzymes that help digest food. In people with cystic fibrosis, mucus blocks the ducts of the pancreas, reducing the production of insulin and preventing digestive enzymes from reaching the intestines to aid digestion. Problems with digestion can lead to diarrhea, malnutrition, poor growth, and weight loss. In adolescence or adulthood, a shortage of insulin can cause a form of diabetes known as cystic fibrosis-related diabetes mellitus (CFRDM).
Cystic fibrosis used to be considered a fatal disease of childhood. With improved treatments and better ways to manage the disease, many people with cystic fibrosis now live well into adulthood. Adults with cystic fibrosis experience health problems affecting the respiratory, digestive, and reproductive systems. Most men with cystic fibrosis have congenital bilateral absence of the vas deferens (CBAVD), a condition in which the tubes that carry sperm (the vas deferens) are blocked by mucus and do not develop properly. Men with CBAVD are unable to father children (infertile) unless they undergo fertility treatment. Women with cystic fibrosis may experience complications in pregnancy.
A defect in the CFTR gene causes cystic fibrosis (CF). This gene makes a protein that controls the movement of salt and water in and out of your body's cells. In people who have CF, the gene makes a protein that doesn't work well. This causes thick, sticky mucus and very salty sweat.
Research suggests that the CFTR protein also affects the body in other ways. This may help explain other symptoms and complications of CF.
More than a thousand known defects can affect the CFTR gene. The type of defect you or your child has may affect the severity of CF. Other genes also may play a role in the severity of the disease.
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
Mutations in the CFTR gene cause cystic fibrosis. The CFTR gene provides instructions for making a channel that transports negatively charged particles called chloride ions into and out of cells. Chloride is a component of sodium chloride, a common salt found in sweat. Chloride also has important functions in cells; for example, the flow of chloride ions helps control the movement of water in tissues, which is necessary for the production of thin, freely flowing mucus.
Mutations in the CFTR gene disrupt the function of the chloride channels, preventing them from regulating the flow of chloride ions and water across cell membranes. As a result, cells that line the passageways of the lungs, pancreas, and other organs produce mucus that is unusually thick and sticky. This mucus clogs the airways and various ducts, causing the characteristic signs and symptoms of cystic fibrosis. Other genetic and environmental factors likely influence the severity of the condition. For example, mutations in genes other than CFTR might help explain why some people with cystic fibrosis are more severely affected than others. Most of these genetic changes have not been identified, however.
Every person inherits two CFTR genes -- one from each parent. Children who inherit a faulty CFTR gene from each parent will have CF.
Children who inherit one faulty CFTR gene and one normal CFTR gene are "CF carriers." CF carriers usually have no symptoms of CF and live normal lives. However, they can pass the faulty CFTR gene to their children.
The image below shows how two parents who are both CF carriers can pass the faulty CFTR gene to their children.
The image shows how CFTR genes are inherited. A person inherits two copies of the CFTR gene -- one from each parent. If each parent has a normal CFTR gene and a faulty CFTR gene, each child has a 25 percent chance of inheriting two normal genes; a 50 percent chance of inheriting one normal gene and one faulty gene; and a 25 percent chance of inheriting two faulty genes.
Cystic fibrosis is a common genetic disease within the white population in the United States. The disease occurs in 1 in 2,500 to 3,500 white newborns. Cystic fibrosis is less common in other ethnic groups, affecting about 1 in 17,000 African Americans and 1 in 31,000 Asian Americans.
The signs and symptoms of cystic fibrosis (CF) vary from person to person and over time. Sometimes you'll have few symptoms. Other times, your symptoms may become more severe.
One of the first signs of CF that parents may notice is that their baby's skin tastes salty when kissed, or the baby doesn't pass stool when first born.
Most of the other signs and symptoms of CF happen later. They're related to how CF affects the respiratory, digestive, or reproductive systems of the body.
Figure A shows the organs that cystic fibrosis can affect. Figure B shows a cross-section of a normal airway. Figure C shows an airway with cystic fibrosis. The widened airway is blocked by thick, sticky mucus that contains blood and bacteria.
People who have CF have thick, sticky mucus that builds up in their airways. This buildup of mucus makes it easier for bacteria to grow and cause infections. Infections can block the airways and cause frequent coughing that brings up thick sputum (spit) or mucus that's sometimes bloody.
People who have CF tend to have lung infections caused by unusual germs that don't respond to standard antibiotics. For example, lung infections caused by bacteria called mucoid Pseudomonas are much more common in people who have CF than in those who don't. An infection caused by these bacteria may be a sign of CF.
People who have CF have frequent bouts of sinusitis (si-nu-SI-tis), an infection of the sinuses. The sinuses are hollow air spaces around the eyes, nose, and forehead. Frequent bouts of bronchitis (bron-KI-tis) and pneumonia (nu-MO-ne-ah) also can occur. These infections can cause long-term lung damage.
Some people who have CF also develop nasal polyps (growths in the nose) that may require surgery.
In CF, mucus can block tubes, or ducts, in your pancreas (an organ in your abdomen). These blockages prevent enzymes from reaching your intestines.
As a result, your intestines can't fully absorb fats and proteins. This can cause ongoing diarrhea or bulky, foul-smelling, greasy stools. Intestinal blockages also may occur, especially in newborns. Too much gas or severe constipation in the intestines may cause stomach pain and discomfort.
A hallmark of CF in children is poor weight gain and growth. These children are unable to get enough nutrients from their food because of the lack of enzymes to help absorb fats and proteins.
As CF gets worse, other problems may occur, such as:
Men who have CF are infertile because they're born without a vas deferens. The vas deferens is a tube that delivers sperm from the testes to the penis.
Women who have CF may have a hard time getting pregnant because of mucus blocking the cervix or other CF complications.
Other signs and symptoms of CF are related to an upset of the balance of minerals in your blood.
CF causes your sweat to become very salty. As a result, your body loses large amounts of salt when you sweat. This can cause dehydration (a lack of fluid in your body), increased heart rate, fatigue (tiredness), weakness, decreased blood pressure, heat stroke, and, rarely, death.
CF also can cause clubbing and low bone density. Clubbing is the widening and rounding of the tips of your fingers and toes. This sign develops late in CF because your lungs aren't moving enough oxygen into your bloodstream.
Low bone density also tends to occur late in CF. It can lead to a bone-thinning disorder called osteoporosis (OS-te-o-po-RO-sis).
Doctors diagnose cystic fibrosis (CF) based on the results from various tests.
All States screen newborns for CF using a genetic test or a blood test. The genetic test shows whether a newborn has faulty CFTR genes. The blood test shows whether a newborn's pancreas is working properly.
If a genetic test or blood test suggests CF, a doctor will confirm the diagnosis using a sweat test. This test is the most useful test for diagnosing CF. A sweat test measures the amount of salt in sweat.
For this test, the doctor triggers sweating on a small patch of skin on an arm or leg. He or she rubs the skin with a sweat-producing chemical and then uses an electrode to provide a mild electrical current. This may cause a tingling or warm feeling.
Sweat is collected on a pad or paper and then analyzed. The sweat test usually is done twice. High salt levels confirm a diagnosis of CF.
If you or your child has CF, your doctor may recommend other tests, such as:
In amniocentesis, your doctor inserts a hollow needle through your abdominal wall into your uterus. He or she removes a small amount of fluid from the sac around the baby. The fluid is tested to see whether both of the baby's CFTR genes are normal.
In CVS, your doctor threads a thin tube through the vagina and cervix to the placenta. The doctor removes a tissue sample from the placenta using gentle suction. The sample is tested to see whether the baby has CF.
People who have one normal CFTR gene and one faulty CFTR gene are CF carriers. CF carriers usually have no symptoms of CF and live normal lives. However, carriers can pass faulty CFTR genes on to their children.
If you have a family history of CF or a partner who has CF (or a family history of it) and you're planning a pregnancy, you may want to find out whether you're a CF carrier.
A genetics counselor can test a blood or saliva sample to find out whether you have a faulty CF gene. This type of testing can detect faulty CF genes in 9 out of 10 cases.
Cystic fibrosis (CF) has no cure. However, treatments have greatly improved in recent years. The goals of CF treatment include:
Depending on the severity of CF, you or your child may be treated in a hospital.
If you or your child has CF, you may be treated by a CF specialist. This is a doctor who is familiar with the complex nature of CF.
Often, a CF specialist works with a medical team of nurses, physical therapists, dietitians, and social workers. CF specialists often are located at major medical centers.
The main treatments for lung problems in people who have CF are chest physical therapy (CPT), exercise, and medicines. Your doctor also may recommend a pulmonary rehabilitation (PR) program.
CPT also is called chest clapping or percussion. It involves pounding your chest and back over and over with your hands or a device to loosen the mucus from your lungs so that you can cough it up.
You might sit down or lie on your stomach with your head down while you do CPT. Gravity and force help drain the mucus from your lungs.
Some people find CPT hard or uncomfortable to do. Several devices have been developed that may help with CPT, such as:
Breathing techniques also may help dislodge mucus so you can cough it up. These techniques include forcing out a couple of short breaths or deeper breaths and then doing relaxed breathing. This may help loosen the mucus in your lungs and open your airways.
Aerobic exercise that makes you breathe harder can help loosen the mucus in your airways so you can cough it up. Exercise also helps improve your overall physical condition.
However, CF causes your sweat to become very salty. As a result, your body loses large amounts of salt when you sweat. Thus, your doctor may recommend a high-salt diet or salt supplements to maintain the balance of minerals in your blood.
If you exercise regularly, you may be able to cut back on your CPT. However, you should check with your doctor first.
If you have CF, you doctor may prescribe antibiotics, anti-inflammatory medicines, bronchodilators, or mucus-thinning medicines. These medicines help treat or prevent lung infections, reduce swelling, open up the airways, and thin mucus.
Antibiotics are the main treatment to prevent or treat lung infections. Your doctor may prescribe oral, inhaled, or intravenous (IV) antibiotics.
Oral antibiotics often are used to treat mild lung infections. Inhaled antibiotics may be used to prevent or control infections caused by the bacteria mucoid Pseudomonas. For severe or hard-to-treat infections, you may be given antibiotics through an IV tube (a tube inserted into a vein). This type of treatment may require you to stay in a hospital.
Anti-inflammatory medicines can help reduce swelling in your airways due to ongoing infections. These medicines may be inhaled or oral.
Bronchodilators help open the airways by relaxing the muscles around them. These medicines are inhaled. They're often taken just before CPT to help clear mucus out of your airways. You also may take bronchodilators before inhaling other medicines into your lungs.
Your doctor may prescribe mucus-thinning medicines to reduce the stickiness of your mucus and loosen it up. These medicines can help clear out mucus, improve lung function, and prevent worsening lung symptoms.
If you have advanced lung disease, you may need oxygen therapy. Oxygen usually is given through nasal prongs or a mask.
If other treatments haven't worked, a lung transplant may be an option if you have severe lung disease. A lung transplant is surgery to remove a person's diseased lung and replace it with a healthy lung from a deceased donor.
Your doctor may recommend PR as part of your treatment plan. PR is a broad program that helps improve the well-being of people who have chronic (ongoing) breathing problems.
PR doesn't replace medical therapy. Instead, it's used with medical therapy and may include:
PR has many benefits. It can improve your ability to function and your quality of life. The program also may help relieve your breathing problems. Even if you have advanced lung disease, you can still benefit from PR.
CF can cause many digestive problems, such as bulky stools, intestinal gas, a swollen belly, severe constipation, and pain or discomfort. Digestive problems also can lead to poor growth and development in children.
Nutritional therapy can improve your strength and ability to stay active. It also can improve growth and development in children. Nutritional therapy also may make you strong enough to resist some lung infections. A nutritionist can help you create a nutritional plan that meets your needs.
In addition to having a well-balanced diet that's rich in calories, fat, and protein, your nutritional therapy may include:
Other treatments for digestive problems may include enemas and mucus-thinning medicines to treat intestinal blockages. Sometimes surgery is needed to remove an intestinal blockage.
Your doctor also may prescribe medicines to reduce your stomach acid and help oral pancreatic enzymes work better.
A common complication of CF is diabetes. The type of diabetes associated with CF often requires different treatment than other types of diabetes.
Another common CF complication is the bone-thinning disorder osteoporosis. Your doctor may prescribe medicines that prevent your bones from losing their density.
If you or your child has cystic fibrosis (CF), you should learn as much as you can about the disease. Work closely with your doctors to learn how to manage CF.
Having ongoing medical care by a team of doctors, nurses, and respiratory therapists who specialize in CF is important. These specialists often are located at major medical centers or CF Care Centers.
It's standard to have CF checkups every 3 months. Talk with your doctor about whether you should get an annual flu shot and other vaccines. Take all of your medicines as your doctor prescribes. In between checkups, be sure to contact your doctor if you have:
Better treatments for CF allow people who have the disease to live longer now than in the past. Thus, the move from pediatric care to adult care is an important step in treatment.
If your child has CF, encourage him or her to learn about the disease and take an active role in treatment. This will help prepare your child for the transition to adult care.
CF Care Centers can help provide age-appropriate treatment throughout the transition period and into adulthood. They also will support the transition to adult care by balancing medical needs with other developmental factors, such as increased independence, relationships, and employment.
Talk with your child's health care team for more information about how to help your child move from pediatric care to adult care.
In between medical checkups, you can practice good self-care and follow a healthy lifestyle.
For example, follow a healthy diet. A healthy diet includes a variety of fruits, vegetables, and whole grains. Talk with your doctor about what types and amounts of foods you should include in your diet.
Other lifestyle changes include:
Although CF requires daily care, most people who have the disease are able to attend school and work.
Adults who have CF can expect to have normal sex lives. Most men who have the disease are infertile (unable to have children). However, modern fertility treatments may help them.
Women who have CF may find it hard to get pregnant, but they usually can have children. If you have CF, you should talk with your doctor if you're planning a pregnancy.
Although CF can cause fertility problems, men and women who have the disease should still have protected sex to avoid sexually transmitted diseases.
Living with CF may cause fear, anxiety, depression, and stress. Talk about how you feel with your health care team. Talking to a professional counselor also can help. If you're very depressed, your doctor may recommend medicines or other treatments that can improve your quality of life.
Joining a patient support group may help you adjust to living with CF. You can see how other people who have the same symptoms have coped with them. Talk with your doctor about local support groups or check with an area medical center.
The symptoms and severity of CF vary. If you or your child has the disease, you may have serious lung and digestive problems. If the disease is mild, symptoms may not show up until the teen or adult years.
The symptoms and severity of CF also vary over time. Sometimes you'll have few symptoms. Other times, your symptoms may become more severe. As the disease gets worse, you'll have more severe symptoms more often.
Lung function often starts to decline in early childhood in people who have CF. Over time, damage to the lungs can cause severe breathing problems. Respiratory failure is the most common cause of death in people who have CF.
As treatments for CF continue to improve, so does life expectancy for those who have the disease. Today, some people who have CF are living into their forties or fifties, or longer.
Early treatment for CF can improve your quality of life and increase your lifespan. Treatments may include nutritional and respiratory therapies, medicines, exercise, and other treatments.
Your doctor also may recommend pulmonary rehabilitation (PR). PR is a broad program that helps improve the well-being of people who have chronic (ongoing) breathing problems.
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