A nurse in an emergency department is caring for an infant who has a 2-day history of vomiting and an elevated temperature. Which of the following should the nurse recognize as the most reliable indicator of fluid loss?

A. Respiratory rate can be influenced by many factors, including fever or anxiety, and is not the most reliable indicator of fluid loss. B. Blood pressure may change with severe dehydration, but it can be a late sign, and other factors (like shock) can also affect blood pressure, so it's not the most reliable early indicator. C. Body weight is the most reliable and sensitive indicator of fluid loss, as even small changes in weight reflect changes in hydration status. Monitoring weight helps assess fluid loss accurately. D. Skin integrity can be affected by dehydration, but it's not the most reliable indicator of fluid loss. It may take longer to show visible signs such as dry skin or poor turgor.