A 9-month-old baby is brought in to the doctor as she has been having a persistent cough, poor weight gain, and has already had several bouts of pneumonitis. On taking the history from the mother, it is known that the baby has been having foul-smelling and very large stools for several months.
Which of the following diagnostic techniques will provide you with the correct diagnosis of this patient?
A- TB skin test
B- CT of the chest
C- Serum immunoglobulins
D- Sweat chloride test