Cystic Fibrosis Essay

spudz22

Hey guys,

I'm doing an essay on cystic fibrosis and I've a few questions!! How is CF diagnosed in newborn babies? Is the salt test still used i.e. salty skin? Any info appreciated

medicinegirl

They use it in hospitals I've been in anyway.
It's known as the sweat test usually, not the salt test but you're right-it picks up the amount of Sodium Chloride the baby secretes.

It's an indicator if CF but has been known to produce false positives- I think genetic testing gives a more definitive answer if there's any doubt

Also as far as I know we don't test for it routinely in Ireland-only if the child appears symptomatic but I stand to be corrected on that!

charlieroot

Was just studying this the other day as part of my paediatrics rotation so its fresh in my head

Diagnosis of CF:
Generally you'll have a high index of suspicion first by taking a history and exam. CF can present in a number of different ways: failure to thrive, recurrent respiratory tract infections, meconium ileus, hyponatraemic dehydration, obstructive jaundice,... (the first two being the most common).

The first line test is a the sweat test. Sweat is collected by pilocarpine iontophoresis (electrical stimulating of your sweat glands). If you get two sweat collections with Cl concentration greater than 60mEq/L on two different days this is diagnostic of CF.

Further to that you can do genetic testing to see what the specific abnormality the person might have. Mutations are classified as:

Class I defective protein production e.g. G542X
Class II defective protein processing e.g. deltaF508
Class III defective regulation e.g. G551D
Class IV defective mRNA stability e.g. R117H
Class V reduced CFTR/partially defective production e.g. A455E

Classification is useful in prognosis as Class I-III generally have pancreatic exocrine insufficiency and so develope CF related diabetes mellitus, while Class IV-V do not. There are also a few treatments in the pipe line that are specific to the type of CFTR defect.

You can in theory also do neonatal screening, you can measure the immuno reactive trypsinogen(IRT) or simply do the genetic testing straight off. However there are a number of problems with this - false positives and a small % of asymptomatic carriers have high IRT. Also patients who are caught later seem to catchup as regards weight and height and there is no evidence that earlier diagnosis translates to better lung function.

charlieroot

medicinegirl wrote: »

Also as far as I know we don't test for it routinely in Ireland-only if the child appears symptomatic but I stand to be corrected on that!

Your right its not screened for in Ireland routinely.

Bicycle

The CF Association are suggesting that routine screening will take place from early next year via a heel prick test
http://www.cfireland.ie/news.php/news/shownews/119

charlieroot

Thanks Bicycle for the info. Do you know by any chance what test they will be using? Is it genetic testing or IRT?