BV is a 19-year-old male who presents to the emergency department complaining of shortness of breath and fever. He has a respiratory rate of 34, temperature of 101.4oF. His SpO2 on room air is 88%. He has a frequent cough productive of small amounts of very thick, dark yellow mucus. He appears to be undersized for his age. Upon questioning, he reveals that he has a history of cystic fibrosis.
Use the Auscultation and Blood Pressure tabs to capture heart rate, blood pressure and lung sounds.
Which of the following is considered to be the gold standard for diagnosing cystic fibrosis?