This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pathology
True about cystic fibrosis 
Select and explain. 
A. The underlying defect in sodium channel function, B. The immune reactive trypsin (I) may be checked on the Guthrie card, C. In most cases the gene c defect is a loss of Valine at position 508 on chromosome 7, D. A sweat test with a sodium content above 40 mmol/l is diagnos c
B: The immune reactive trypsin (I) may be checked on the Guthrie card
Answer: B: The immune reactive trypsin (I) may be checked on the Guthrie card 
Explanation: The immune reactive trypsin (I), used in diagnosis of those under 3 months can be checked on the Guthrie card. The sweat sodium concentrate on is the definitive test and this is diagnostic if on two tests the sodium is above 60mmol/l. False positive sweat tests are seen in Ectodermal Dysplasia.