Final answer:
A patient should be informed that an I131 test is used to evaluate thyroid function, by assessing how much radioactive iodine is absorbed by the thyroid gland versus how much is excreted in the urine. Option C is correct.
Step-by-step explanation:
The question is about what a patient should be taught regarding an I131 test, which is used to evaluate thyroid function. When performing the I131 test, a small dose of radioactive iodine is administered, and the amount excreted in the urine is measured.
If the amount of I131 in the urine is near the amount given, it indicates that the thyroid gland may not be functioning properly. Conversely, if the amount is significantly lower, it indicates normal thyroid gland function as the gland has absorbed the iodine.
This assessment is important in the context of diagnosing conditions related to thyroid gland function, like hyperthyroidism or hypothyroidism. Education for a patient about the I131 test should therefore include information about its purpose, which is to monitor thyroid function and not other indicators like blood glucose levels, kidney function, or cardiac output.