Cystic fibrosis is a chronic lung disease that occurs due to specific genetic mutations. The symptoms of cystic fibrosis worsen with age and become hard to ignore, so the condition usually gets detected much before the individual reaches adulthood. One of three types of tests is conducted as part of cystic fibrosis diagnosis, to check if the individual is carrying the mutated gene responsible for this condition.
Cystic Fibrosis Diagnosis – A History Of The Disease
Cystic fibrosis was first diagnosed in the year 1938 by Dr. Dorothy Andersen, in New York Babies Hospital. In 1989, a team of geneticists headed by Dr. Tsui Lap-chee from the Hospital for Sick Children, Toronto found the cause of this condition to be a mutation in the gene CFTR (Cystic Fibrosis Transmembrane Regulator).
So far, more than 900 mutations have been found in the CFTR gene.
The Three Tests Used In Cystic Fibrosis Diagnosis
Several diagnostic tests have been developed to detect cystic fibrosis even before its symptoms start to appear. Cystic fibrosis diagnosis can be made at three different stages of life: before birth (prenatal diagnosis), after birth (postnatal diagnosis), and during early childhood.
This test is usually done to check if the unborn child has cystic fibrosis, when either of the parents or both of them are known to be carriers of the defective CFTR gene. In this test, the CFTR gene is screened for mutations that are associated with cystic fibrosis.
If the test reveals that the unborn child has cystic fibrosis, it helps the parents decide if they want to continue with the pregnancy or not. If they decide to continue with it, then they have the advantage of receiving early and timely treatment for their child. There are two common types of prenatal tests:
- Amniocentesis: This test is usually carried out between the 15th and the 18th week of the pregnancy. A sample of the amniotic fluid that surrounds the unborn child in the uterus is taken using a fine needle, for testing.The DNA is isolated from this sample and the CFTR gene is screened for mutations. By analyzing the mutations, the doctors can determine if the unborn child has cystic fibrosis or not.The fetal enzymes in the sample are also tested to aid the diagnosis. If the level of enzymes appears decreased, it indicates that the child has cystic fibrosis.
- Chorionic Villus Sampling: This test is usually carried out when the pregnancy is between 11 and 14 weeks. A small amount of tissue sample is taken from the chorionic villus region of the placenta, using a small needle. Again, the DNA is isolated from the tissue sample and screened for mutations in the CFTR gene to determine if the unborn child has cystic fibrosis or not.
Both these tests provide 99% precision in determining whether the unborn child has this lung disease or not. However, there is a 1-2% chance of a miscarriage after the tests are carried out because of probable infections caused during the sample collection.
Postnatal Screening Or Newborn Screening
A test known as Immunoreactive Trypsinogen Test (IRT) is carried out about 2 to 3 days after the birth of the child. This test measures the level of the protein trypsinogen. High levels of this protein usually indicate cystic fibrosis.
Early Childhood Test (Sweat Test)
The Sweat Test is the most common test widely used for the diagnosis of cystic fibrosis in children and young adults. This test is a rapid and painless procedure in which the levels of sodium and chloride are measured in the sweat excreted from the individual’s body.
As part of this test, a chemical called pilocarpine is applied to the forearm of the subject and a mild electric current is applied to the area where sweating is experienced. Higher than usual levels of sodium and chloride usually indicate cystic fibrosis.
Other tests like lung function tests, chest X-rays, sputum cultures, and stool examinations are also commonly used as part of cystic fibrosis diagnosis. It is important to test for the condition and start cystic fibrosis treatment as soon as possible to manage the condition better.