Final answer:
The nurse would intervene if the client says they will void and discard the urine before the test begins.
Step-by-step explanation:
The nurse would intervene if the client says, 'I will void and discard the urine before the test begins.' It is important to collect all urine over the 24-hour period for an accurate creatinine clearance test. Discarding urine before the test begins would result in an incomplete collection and inaccurate results.