![image image](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgqXgMECVPhIJCmkb1uf_i-c9ciKnJgvGW9aPyUjCLy4RA-aJV6A7K7BzH_cja1RHIW5zyw7oNlHRi9ORd6uMvbhde64X4TZOTNEBrChi1BfK-1ANN-NH_MeE-nx9SlgcA8mvjLE_B4miur/?imgmax=800)
Abdominal distension and muscle wasting is present in this boy who presented with a history of frequent loose bulky stools and poor weight gain. Over 90% of cystic fibrosis patients have intestinal malabsorption due to pancreatic insufficiency.
what's the single most specific test to diagnosis this condition ?