Final answer:
The critical laboratory datum necessary before a PET scan is the fasting blood glucose level, as it influences the uptake of glucose-based radiotracers used in the scan. B) Blood urea nitrogen (BUN)
Step-by-step explanation:
Before undergoing a positron emission tomography (PET) scan, it is essential to assess the client's renal function to ensure the safe administration and clearance of the radiopharmaceutical used during the procedure. The fasting blood glucose level is a critical laboratory datum to obtain prior to a PET scan.
This test is important because the radiotracers used during a PET scan, such as fluorodeoxyglucose (18F-FDG), are similar to glucose and any deviations in blood glucose levels can affect the distribution and uptake of the tracer, influencing the scan results. Information on Blood Urea Nitrogen (BUN) and Creatinine, while important in assessing kidney function, are not typically the primary concern before a PET scan that uses glucose-based radiotracers.