Final answer:
Prior to excretory urography, radiographers must check the blood chemistry levels of creatinine and blood urea nitrogen (BUN) to assess kidney function, as they are critical indicators of renal health. RBC levels are not a primary concern for this procedure.
Step-by-step explanation:
Before excretory urography, it is essential for the radiographer to check certain blood chemistry levels to assess renal function and ensure the patient's safety. Particularly, levels of creatinine and blood urea nitrogen (BUN) are crucial, as these are primary indicators of kidney function. The normal ranges for these tests typically range from 0.8-1.2 mg/dl for creatinine in males, 0.6-0.9 mg/dl in females, and 8-20 mg/dl for BUN. Checking these levels can help to avoid potential complications that can arise from impaired kidney function, such as contrast-induced nephropathy. Red blood cells (RBCs), on the other hand, are not directly related to kidney function and are therefore not a primary concern in preparation for excretory urography.