How do you know if you have it?

In Australia, newborn screening of CF is used in all states and territories. Newborn screening is a method that detects approximately 95% of babies born with CF. This test is conducted 48 to 72 hours after birth when a sample of blood is collected by heelprick onto a Guthrie card. The Guthrie card is used to test for a number of diseases.

From the dried blood on the Guthrie card, levels of immunoreactive trypsinogen (IRT) are measured. Trypsinogen is produced by the pancreas and transported to the intestine. In the intestine it is turned into the enzyme trypsin that helps with digestion. In CF mucous plugs can obstruct the pancreas ducts and stop the trypsinogen from reaching the intestine. In CF the levels of trypsinogen in the blood is raised. If the levels of trypsinogen are high the blood is tested for common CF mutations (see ‘what are genotypes’).

If two mutations are found then a CF diagnosis is made. If one CF mutation is identified then a sweat test is performed 3 to 4 weeks later. In a sweat test a small amount of sweat is collected from your baby. We are looking for levels of sodium and chloride (salt). Most infants will have a negative test and be carriers of CF. About 1 in 10 children will have a positive test and they will have CF.