Hello and welcome to the site. <img src="i/expressions/rose.gif" border="0"> We are here to support you through this process and answer any questions you have... First of all, congratulations on the birth of your new little girl. I hope everything else is going well with her and you are able to enjoy these precious early days with her despite your worries over this. <img src="i/expressions/heart.gif" border="0">
Re. your question about the IRT test> as you may have been told, the IRT is a screening test, not a diagnostic one, which is why it must be followed up by a sweat test and/or genetic testing in an effort to confirm or rule out a diagnosis. In actuality, most babies with an elevated IRT do NOT have CF! But due to the importance of accurately diagnosing those that do, all babies with a positive result must be tested to be sure and any worrisome symptoms followed up on.
What the IRT was looking for: it checks for levels of something called "immunoreactive trypsinogen", an enzyme produced by the pancreas that is often elevated in newborns that have cystic fibrosis. When it is elevated, it is followed up by a sweat test in most states, a genetic test in some.
The sweat test will be looking for abnormally high levels of sodium chloride and is not an invasive test at all. CF is caused by a genetic defect that, among other things, will usually result in sweat having higher levels of salt in it than usual. This test is more accurate if performed on babies past the newborn stage but results may still be lower than they would be w/ someone older. Genetic testing looking for the mutations that cause the disease can also be done, since sweat test values can vary dramatically. How they proceed with this will depend on what symptoms are also seen with the baby.
How is she doing- have there been any symptoms of concern (respiratory- i.e. congestion or cough, or digestive- weight loss, other than what is expected immediately following birth, abnormal stools, etc?)
I hope all turns out well, that your daughter does not turn out to have cf.