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Cystic Fibrosis Testing and Diagnosis

Like many congenital conditions, some cases of cystic fibrosis are more severe than others. Symptoms may be evident at birth or not appear until well into adulthood.

While about 15 percent of cases aren't diagnosed until childhood or later, thanks to advances in medical technology, tests such as genetic screenings, prenatal screenings and, in all states, required newborn screenings, more and more cases are being detected in newborns ... and even earlier. These early diagnoses help to ensure that people with CF get to live longer healthier lives.

Of course, testing doesn't stop with the initial diagnosis. CF patients deal with many medical challenges, and have risks for developing infections and related conditions such as diabetes, liver damage and lung disease or damage. For that reason, the kids, teens and adults we see in our CF Center are tested for varying issues on a quarterly and annual basis, as well as anytime there is a suspected issue or condition.

To help you understand the testing, we've provided information on the most common tests we perform, both for initial diagnosis and in our ongoing care.

Cystic fibrosis carrier testing

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.

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. And, if both you and your partner are carriers, the chances that you'll have a child with CF increase.

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.

Pulmonary function test

Pulmonary function test – also called spirometry, or breathing test, is a quick test to see how well you or your child's lungs are working. The test doesn't hurt and usually includes a mouthpiece and noseclips. The test is usually attempted by the time you reach the age of 5. Lung volume testing is an additional test that is performed when you or your child turns 8 years old.

Genetic testing

Every person with CF was born with CF. It's a genetic disease that begins with conception. Each person with CF got a gene for this disease from both the mother and the father. Therefore, a CF fragment gene is present on both sides of the family.

The CF gene was identified in 1989. Finding the gene and learning why it causes CF has led to research on new ways to treat CF. All people with a positive sweat test should have a genetic test done to find which genes are causing the disease. This will help guide treatment as we learn more about the genetics of CF and new treatments are developed.

Prenatal screening

If you're pregnant, prenatal genetic tests can show whether your fetus has CF. These tests include amniocentesis (AM-ne-o-sen-TE-sis) and chorionic villus (ko-re-ON-ik VIL-us) sampling (CVS).

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 your baby. The fluid is tested to see whether both of your 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 your baby has CF.

Newborn screening

All newborns are screened for certain conditions before they go home for the first time. One of those conditions is cystic fibrosis. The earlier it's detected, the sooner treatment can begin, and that means reducing the long-term damage that can occur. Your baby may have had a positive result which MIGHT mean he or she has cystic fibrosis. However, to be certain, your doctor may refer you for testing so that, if necessary, treatment can begin.

On the day of your visit:

  • Do not use any lotions, creams or moisturizing soaps on your baby.
  • Bring an extra blanket or sweater and hat to keep your baby warm and help them sweat during the test.
  • Please arrive at least 30 minutes prior to your appointment time to assure that you have time to fill out any additional paper work, and to prepare for the test.
  • Check-In on the 1st floor of Dodson in Registration then with receptionist at the Pulmonary Clinic.
  • Make sure you bring your insurance information and a photo ID, such as a driver's license.
  • The test will take approximately one hour to complete.

It's also important to know that newborn screening won't detect all cases of CF.  Children with symptoms of CF as they get older should be re-evaluated for CF.

Sweat test

People with CF have too much salt in their sweat, in fact, they can have two to five times the normal amount of salt of those who don't have CF. If a genetic test or blood test suggests CF, a sweat chloride test helps diagnose CF by measuring the amount of salt in sweat.

This test can be performed in people of all ages. For an infant suspected of having cystic fibrosis, the test can be performed as early as 48 hours after birth, though any test conducted during a baby's first month might need to be repeated because newborns may not produce enough sweat to ensure reliable results. Sweat tests may also be ordered for kids, teens and adults with a family history of cystic fibrosis or symptoms of the disorder. Symptoms and signs include failure to grow, repeated lung infections, and digestive problems.

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.

For children who are less than six months old:

  • Chloride levels at or above 60 mmol/L (a measure of concentration) means the child has CF.
  • Chloride levels between 30 and 59 mmol/L are considered borderline and need to be examined on a case-by-case basis.
  • Chloride levels below 30 mmol/L are considered negative for CF.

For people over the age of six months:

  • Chloride levels at or above 60 mmol/L means the person has CF.
  • Chloride levels between 40 and 59 mmol/L are borderline.
  • Chloride levels below 40 mmol/L are considered negative for CF.

Sometimes the results are "borderline" and will require additional testing. Results are available within 1-2 business days. 

Preparing for a sweat test

No special preparation is necessary for this test. Before having this test, your child may eat, drink, and exercise as usual, and continue to take any current medications. Creams and lotions should not be applied to the skin 24 hours before the procedure. A sweat test usually takes about an hour, so you may want to bring books or toys to help your child pass the time.

How the test is done

An area of skin on the arm will be washed and dried. Next, two electrodes are attached with straps. One of these contains a disc with pilocarpine gel, a medication that stimulates the sweat glands to produce sweat. The medication is pushed through the skin by a weak electric current. After this is completed, the electrodes are removed and the skin is cleansed.

A special sweat collection device is then attached to the clean skin surface in the area where the sweat glands were stimulated. It's taped to the skin to keep it from moving. The sweat is collected for 30 minutes. The sweat that's collected turns blue when it comes into contact with blue dye within the collector, making it visible to the technician.

After sufficient sweat accumulates in the tubing inside the collector, it's removed and placed in the sweat analyzer. The collector apparatus is removed and the arm is cleaned again. Your child's skin may remain red and continue sweating for several hours after the test.

What to expect

This test shouldn't be painful, though some kids do feel a slight tingling or tickling sensation when the electrodes apply current to the skin.

Preparing your child

Explaining the test in terms your child can understand might help ease any fear. Also reassure your child that the procedure doesn't hurt. You may choose to stay with your child to help keep him or her distracted during the test.

The results

A sweat chloride level of more than 60 millimoles per liter is considered abnormal and indicates the high likelihood of cystic fibrosis, though some people with CF do have borderline or even normal sweat chloride levels. If more sweat is needed, the test might be repeated. If results are positive or unclear, a blood test may be done, especially for babies.

Sputum culture

Kids with cystic fibrosis (CF) tend to get frequent respiratory infections, sometimes caused by bacteria or fungi. A sputum (mucus) CF respiratory screen or culture helps doctors detect and identify these bacteria or fungi so they can prescribe the most effective antibiotics to target a specific infection.

Why It's Done

A sputum culture can help identify specific causes of infections in the lungs and airways. Such infections can lead to coughing that produces yellow, greenish, or blood-tinged sputum, in addition to fever and difficulty breathing.


Before the test, be sure to tell the doctor whether your child has taken antibiotics recently. The best time for testing is usually in the morning, before your child has had anything to eat or drink. Also, make sure your child doesn't use mouthwash before the test because it may contain antibacterial ingredients that could affect results.

The Procedure

Your child will be asked to rinse his or her mouth out with water, then breathe deeply and cough deeply to produce sputum from the airway.

You or the health professional helping your child may need to gently tap on your child's chest to loosen the sputum in the lungs. If your child can't produce a sample, the lab technician may need to use a tongue depressor to stimulate a cough, or your child may need to inhale a mist solution to help produce a cough.

If your child is scheduled for a bronchoscopy (a test done with a small telescope to evaluate the upper airway and bronchi), a sputum screen is likely to be done at this time.

What to Expect

Your child may experience mild discomfort when taking a deep breath or coughing. If your child inhales the mist solution, the urge to cough may be strong. It may take several attempts at coughing to produce the amount of sputum needed for the test.

Getting the Results

The sputum sample is collected into a sterile container and sent to a laboratory. The sample is then placed on a special plate that enables growth of certain bacteria and fungi if an infection is present.

If your child has a bacterial infection, the organisms may need 48 hours to grow. Fungi need a week or longer. These organisms will be identified under a microscope or through chemical tests. If the tests indicate an infection, an additional 1-2 days may be required to determine which antibiotic is best suited to treat it.


Coughing to produce the sputum specimen may be mildly uncomfortable, but there are no risks associated with this procedure.

Throat culture

Kids with cystic fibrosis (CF) tend to get frequent respiratory infections, sometimes caused by bacteria or fungi. Such infections can lead to coughing that produces yellow, greenish, or blood-tinged sputum, in addition to fever and difficulty breathing. A throat culture can help your doctor detect the cause. The most common diagnosis is strep throat, which can be especially harmful to someone with CF.

Preparing for the test

On the day of the test you'll be asked to not use antiseptic mouthwashes before your test. The antiseptic can temporarily mask or kill important germs and the test may have to be performed again.

How the test is done

Throat cultures can typically be done in the doctor's office. They require no medication. The patient's head is tilted back and the mouth opened wide. The doctor or nurse will then rub a sterile swab along the back of the throat several times to gather as much specimen as possible.

Blood work

Blood work is tested on a regular basis because people with CF are prone to diabetes and liver disorders. Blood samples will be tested for glucose (blood sugar) level and for liver function. The liver regulates your blood, including sugar, protein and fat. It also removes toxins from your blood. Because CF can interfere with the liver's ability to function correctly, testing the blood can help to detect a problem and treat it before it creates long-term damage.

A complete blood count will also be taken. This is the most common blood test, and measures the three major types of cells in blood: red blood cells, white blood cells, and platelets. The test can check for infections, and can tell if the patient has any side effects from medications.

A small sample is collected from a finger, a heel (in infants), or from a vein. A machine then processes the sample, counting cells, measuring hemoglobin (the part of red blood cells that carries oxygen), and sorting the white blood cells into five subtypes. Results are often available the next day.


Depending on the diagnosis and symptoms, your doctor may order either a chest X-ray or a sinus X-ray. In some case, both may be needed.

A chest X-ray creates pictures of the structures in your chest, such as your heart, lungs, and blood vessels. A chest X-ray can show whether your lungs are inflamed or scarred, or whether they trap air.

A sinus X-ray is done to look for signs of sinusitis, a complication of CF.


It's not uncommon for some CF patients, kids, teens and adults, to occasionally develop a respiratory infection. If your doctor suspects that you may have an infection or other type of blockage, you may undergo a test called a bronchoscopy. Using a special scope called a bronchoscope, we can look inside your child's respiratory system to find any infection or abnormality that might be there. The scope also lets us vacuum liquid from the linings of the airways to take a specimen for culture, diagnosis and biopsy.

How is the bronchoscopy done?

The bronchoscopy is typically done in a surgical suite, either outpatient or inpatient, depending on your circumstances. Patients are sedated so that they're asleep during the procedure. In some cases where a biopsy is performed or small pieces of tissue are collected, general anesthesia may be required. Once the patient is asleep, medication is applied through the bronchoscope to numb the nose and back of the throat as well as other parts of the airway. This is done to reduce irritation as well as coughing and sneezing.

The procedure takes about 45 minutes. Once it's completed, the patient is taken to recovery until he or she is ready to return home or to their room.

Kidney function tests

Kidney function tests measure the health of the kidneys, which filter your blood of wastes. The tests check the amount of waste products passed in urine or left in the blood, and also check the blood's mineral levels. The tests can tell if the kidneys aren't functioning as they should, or if medications used to treat CF are affecting the kidneys.

For a blood test, a sample is drawn from a vein—usually from the inside of the elbow or the back of the hand—with a thin needle. For a urine test, the patient urinates in a small jar to collect the sample. In both cases, the samples are sent to a lab for analysis.

Liver function tests

Liver function tests can tell if the liver has been injured by disease or other factors. The liver stores enzymes for digestion, and injury to the liver can release some of these enzymes into the blood. Blood tests measure the level of enzymes in the blood, and can indicate liver damage, or blockage in the ducts around the liver.

Blood is drawn from a vein using a thin needle. The sample is then sent to a laboratory for analysis. Results are often available the next day.

Oxygen saturation test

Red blood cells carry oxygen to the organs of the body. When these red blood cells pass through the lungs, they emerge saturated with oxygen. In a patient with lung disease, or another lung condition, not all of these red blood cells leave the lungs carrying oxygen. An oxygen saturation test measures the percentage of red blood cells that carry oxygen. It can tell if a person's lungs aren't working as well as they should.

In most cases, our office will use a simple detector that fits on a finger to estimate oxygen saturation. To get a more accurate reading, a doctor will draw blood from an artery in the wrist—where the pulse is normally taken—and then test the blood for its oxygen level. The results of this test are usually available within a half-hour.

Oral glucose tolerance test

The oral glucose tolerance test (OGTT) is used to check for CF-related diabetes (CFRD), one of the most common CF-related complications. This test checks how well your pancreas is doing at keeping your blood sugars under control. CF-related diabetes is very different from the diabetes found in people who don't have CF. CF-related diabetes can lead to a drop in your lung function as well as unhealthy weight loss, so finding it and treating it's very important. That's why an oral glucose tolerance test is required every year starting at age 10.

An oral glucose tolerance test is a fasting lab, so it's important not to eat or drink anything besides water for at least 8 hours before coming to the lab. It's usually easiest to do this test first thing in the morning and scheduled separately from your office visit. The test itself takes about 2.5 hours.

What you can expect during your test:

  • First, your blood sugar will be checked.
  • Next, you'll be given a special sweet beverage to drink within 5 minutes.
  • Then, you'll need to stay at the lab for 2 hours and your blood sugar will be checked again.

Our CF center will notify you of your results.

We're here to help.

If you have been told your child might have CF, we know you have lots of questions. We can help. To schedule an appointment, refer a patient or speak to our staff, please call our offices at 682-885-6299. After hours and on weekends/holidays, call 682-885-4000 and ask the operator to page the pulmonologist on call.