Cystic Fibrosis testing: Genetic testing and sweat test
lightNlife
November 22, 2015
Written by LightNLife and Ambry Genetics
updated by Melissa75
How many different CF mutations are there?
More than 2000 and new ones being added all the time.
http://www.genet.sickkids.on.ca/cftr/StatisticsPage.html
What is meant by a “panel” test?
A panel tests for a predefined number of mutations. It’s possible that a panel tests can miss a rare mutation.
My panel came back negative but my sweat test is positive. Do I have CF?
A positive sweat test used to be the “Gold Standard” for determining whether a person has CF. It may be helpful to get a more comprehensive panel that looks for more mutations or have a genetic sequencing test performed in order to have a definitive answer.
How many genes does the Ambry Test look for?
Ambry initially screens for ΔF508, the most common CF mutation. Testing continues with CF AMPLIFIED for diagnostic patients who do not have homozygous ΔF508. CF AMPLIFIED is the most comprehensive CF test available, detecting approximately 99% of mutations, including gross deletions and duplications, in patients of all ethnicities. The test begins with full gene sequence analysis which detects 97-98% of mutations.
My child has a rare mutation. Will the Ambry test be able to determine which one it is?
99% of mutations are rare. This means that they occur less than .1% of the time.
How long does it take to get results back from Ambry?
Typical turnaround is 2-4 weeks.
What numbers on a sweat test indicate a positive test for CF?
39 and below is considered normal (usually no CF).
40-60 is considered borderline.
Above 60 is positive for CF.
Edited: The latest sweat test guidelines change the borderline or “possible” category to above 30 mmol for all ages. https://cysticfibrosis.com/new-guidelines-cf-diagnosis/
Is there a correlation between type of mutation and severity of the disease?
Generally the milder mutations are indicative of milder disease, but there is variability of symptoms even among patients with identical mutations.
I don’t live in the United States. Can I still have the Ambry test done?
Yes. You can use Ambry from anywhere in the world.
I would like to have my spouse carrier tested. Does Ambry do this?
Yes.
My spouse tested negative as a CF carrier, and I have CF. Does this mean we won’t have a child with CF?
When one parent has CF, there is never a zero percent chance that the child will not have CF because there are still some mutations that have not been identified. However, the risk of the child having CF is about 1 in 4800 as compared to 1 in 3,000 in the normal population.
My spouse and I are not Caucasian. Does this mean our child won’t have CF?
No. We see CF in all ethnic groups all the time. It is definitely not as common in the African American and Asian populations but it occurs in every group, just not as often. DeltaF508 is still seen as one of the more common mutations in many other ethnic groups as well. There are many physicians who still do not think of CF outside of the Caucasian populations. As we learn more and more about CF mutations, we are always trying to educate the medical community.
