Yes I am aware that they are the median values, I mentioned that in the post about sweat chloride. I was trying not to be too technical when I wrote 'normal', this is easier for most people to understand over median.
I'm not sure if you have read the article but here are some more figures: The estimated median (95% RI) for sweat chloride were: 5 to 9 years, 13 mmol/L (1-39 mmol/L); 10 to 14 years, 18mmol/L (3-47 mmol/L); 15 to 19 years, 20 mmol/L (3-51mmol/L); and 20+ years 23 mmol/L (5-56mmol/L). The 95% RIs are similar to the values that were found in each of the groups (the article has a dot plot showing this).
So yes according to that data up to 39 is 'normal' at age 5-9. If I take that further my 54 at age 27 is also 'normal.'
The numbers are postively skewed, eg with age 5-9 half the people are between approx 1-13 and the other half between 13-39 (75th centile at about 19, so 75% below about 19). There may be some non F508del carriers in the higher range of normal in this study.
I'm hesitant to write that a level is normal as I am aware that G551D with Kalydeco has about 50% CFTR function. So my 54 is in the grey zone, I know some people who have been diagnosed with CF with a similar sweat chloride, and according to that study, some people also have that sweat chloride and do not have CF. I agree that 14 and 17 seem normal for a 5-9 year old, but for those of us in the grey area I personally dont use the word normal (ie the borderline between normal/not normal is hard to define).
Whenever I write about scientific studies I am very cautious about what I write (eg use words like may or could instead of definite words) which is why I used pretty much normal.