Final answer:
The nurse should prioritize reporting 'Hemoptysis 275 mL/24 hours' to the provider because it signifies a severe and potentially life-threatening condition in a child with cystic fibrosis, necessitating urgent medical attention.
Step-by-step explanation:
The priority finding the nurse should report to the provider for a school-age child with cystic fibrosis is B) Hemoptysis 275 mL/24 hours. This symptom indicates a severe lung hemorrhage that can be life-threatening, requiring immediate medical intervention. Hemoptysis at this volume significantly surpasses normal expectoration and can swiftly lead to respiratory failure. While decreased activity, fever, and weight loss are also concerning findings, the threat posed by significant hemoptysis is far more acute and could imply a major deterioration in the child's respiratory status. In cystic fibrosis, the lungs are already compromised by thick, viscous mucus; bleeding of this extent compounds the risk of infection, further lung damage, and impaired gas exchange. The other symptoms should still be communicated to the provider, but they are not as immediately life-threatening as severe hemoptysis.