I can't answer the first part of the question because I simply don't have the answer about right/left arm, although I'm sure someone does.
As far as the genetics, A person who has 1 CF mutation is considered a carrier. A person who has 2 CF mutations HAS the Cystic Fibrosis disease. Here's a link to my website where I have some more information about the passing down of mutations and a table (I'm a visual person) that might help put it in perspective. <a target=_blank class=ftalternatingbarlinklarge href="http://www.cysticfibrosismaleinfertility.com/Where_to_begin_carrierTesting.html
">http://www.cysticfibrosismalei...n_carrierTesting.html
</a>
What Josh's doctor is checking for is to see if he carries 2 CF mutations, and therefore has CF. The genetic testing is not 100% either (just like the sweat test) because most doctors only test for the most common CF mutations, which is between 25-97. There are currently 1300 KNOWN CF mutations and more found all of the time, so a genetic test is not 100% conclusive EVEN if you go with the extended panel test. So it would be very necessary for your son to have an extended panel test through something like Quest Diagnostics or Ambry Genetics. It is quite a bit more expensive but they test for the 1300 known mutations.
Best of luck and keep us posted!
