A mother brings her 2-month-old to the well-baby clinic. She states that when she kisses her baby, the infant’s skin tastes salty. The nurse should prepare the mother for what standard diagnostic test to screen for cystic fibrosis (CF)?

Choice A rationale A fecal-fat test is used to measure the body’s ability to break down and absorb fat. It is not used to screen for cystic fibrosis. Choice B rationale The sweat-chloride test is the standard diagnostic test for cystic fibrosis. This test measures the amount of chloride, a component of salt, in the sweat. People with cystic fibrosis have two to five times the normal amount of chloride in their sweat. Choice C rationale A pulmonary-function test measures how well the lungs are working and can be used to monitor the lung function in people already diagnosed with cystic fibrosis. However, it is not a standard screening test for cystic fibrosis. Choice D rationale A potassium chloride test is not used to screen for cystic fibrosis. Potassium chloride is a type of medication used to treat or prevent low amounts of potassium in the blood.