How Is Cystic Fibrosis Diagnosed?
Doctors diagnose cystic fibrosis (CF) based on the
results from various tests.
Newborn Screening
Most 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.
Sweat Test
If a genetic test or blood test suggests CF, a
doctor will confirm a diagnosis using a
sweat
test. This test is the most useful test for diagnosing CF. It measures the
amount of salt in sweat.
For this test, doctors trigger sweating on a small
patch of skin on an arm or leg. They rub the skin with a sweat-producing
chemical and then use 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.
Other Tests
If you or your child has CF, your doctor may
recommend other tests, such as:
- Genetic tests to find out what type of CFTR
defect is causing your CF.
- A
chest
x ray. This painless test creates pictures of the structures in your chest,
such as your heart and lungs. A chest x ray can show whether your lungs are
inflamed or scarred or whether they trap air.
- A sinus x ray. This test may show signs of
sinusitis, a complication of CF.
-
Lung
function tests. These tests measure the size of your lungs, how much air
you can breathe in and out, how fast you can breathe air out, and how well your
lungs deliver oxygen to your blood.
- A sputum culture. For this test, your doctor will
take a sample of your sputum (spit) to see what bacteria are growing in it. If
you have bacteria called mucoid Pseudomonas, you may have more advanced CF that
needs aggressive treatment.
Prenatal Screening
If you're pregnant, prenatal genetic tests can find
out 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 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.
Cystic Fibrosis Carrier Testing
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 see whether you have a faulty CF gene. This type of testing can
detect faulty CF genes in 9 out of 10 cases. |