A 10-year-old boy presents with a history recurrent abdominal pain. There is a past history of bronchitis but no history of pneumonia. On examination, there has been no significant increase in weight over the past 3 years, with flattening of the growth curve. Trace digital clubbing is noted. Most appropriate test to be ordered at this time is?

Sweat test. The most common cause of digital clubbing in children, other than cyanotic congenital hea disease, is cystic fibrosis. The history of bronchitis and of abdominal pain (probably secondary to malabsorption) is compatible with this diagnosis. Therefore, a sweat test is the best test to order. Pulmonary function tests are not diagnostic but may suggest obstructive pulmonary disease; a chest x-ray may show chronic changes; an abdominal x-ray may show dilated loops of filled bowel; and an IgE level may demonstrate allergies as the etiology of the bronchitis. Only the sweat test is diagnostic