Which vital sign was noted to be abnormal for the 19-year-old student with strep throat suggesting possible dehydration?

An elevated heart rate can indicate dehydration, especially in a young person who is ill, such as a 19-year-old student with strep throat. When dehydration occurs, the body's blood volume decreases, leading the heart to pump more quickly to maintain adequate circulation and ensure that vital organs receive enough blood.

In the context of strep throat, symptoms such as sore throat, fever, and difficulty swallowing may lead to reduced fluid intake, increasing the risk of dehydration. An increased heart rate is one of the body’s compensatory mechanisms to help maintain homeostasis when fluid levels are low.

While body temperature, blood pressure, and respiratory rate can provide important information about a person's health status, they do not directly indicate dehydration in the same way that a change in heart rate does. Elevated body temperature may result from infection, blood pressure may remain stable until dehydration is severe, and respiratory rate is more influenced by other factors. Thus, the heart rate serves as a key indicator in this scenario, pointing to the possibility of dehydration.