How Is Cystic Fibrosis Diagnosed?
First, your doctor will obtain a detailed medical and family history and perform a thorough physical examination. Next, your doctor may order some tests to ensure an accurate diagnosis.
The sweat test is the most useful test for diagnosing cystic fibrosis (CF). It measures the amount of salt in your sweat. For this test, doctors rub a small amount of a chemical called pilocarpine (pi-lo-KAR-pen) on your arm or leg. They then attach an electrode to this spot. The electrode provides a mild electric current that produces sweat. This may cause tingling or a feeling of warmth. They then cover the area with a gauze pad or filter paper and wrap in plastic. After 30 to 40 minutes, they remove the plastic so the sweat that collected on the pad or paper can be analyzed. The test is usually done twice. High salt levels mean CF.
Your doctor may also do the following tests to understand more about your condition and how to treat it:
Blood tests to look for an abnormal CF gene or other things that indicate CF.
Chest x ray. A chest x ray takes a picture of your lungs. It can show scarring from inflammation in your lungs.
Sinus x ray. This test may show signs of sinusitis.
Lung function tests can measure:
How much air your lungs can hold
How quickly you can breathe air out of your lungs
How well your lungs add oxygen to and remove carbon dioxide from your blood
Sputum (phlegm) cultures. Doctors take a sample of your sputum to see what bacteria are growing in it.
If you are pregnant, prenatal genetic tests can find out if your baby has CF:
In amniocentesis (AM-ne-o-sen-TE-sis), your doctor inserts a hollow needle through your abdominal wall into your uterus to obtain cells from the fluid (amniotic fluid) around the baby. The fluid is then tested to see if both of the baby's CFTR genes are normal.
In a chorionic villus biopsy (ko-re-ON-ik VIL-us BI-op-se), your doctor uses ultrasound to guide a thin tube through your vagina and cervix into your uterus and remove a tiny piece of the placenta to biopsy. The cells of the placenta are then tested to see if the baby has CF.
Some States are now testing the blood of all newborns for CF.
CF Carrier Testing
You may want to check whether you are a CF carrier, if:
You have a family history of CF.
You are a partner of someone with CF.
You are a couple planning a pregnancy.
A genetics counselor at your local hospital can take a blood or saliva sample to see if it contains the abnormal CFTR gene that causes CF. It will detect 9 out of 10 cases of CF. Some insurance plans cover genetic testing.
