WHAT IS RENOCYSTOGRAM (RENOGRAM SCAN, RENAL SCAN) TEST?
The renocystogram is a dynamic nuclear medicine study of the kidneys and ureters in which the dispersion, clearance, and excretion of a radionuclide are recorded by means of a gamma radiographic scan. Radionuclide uptake, transit, and excretion times are computed, and renogram curves are plotted on a graph for each kidney and ureter. Quantitative evaluation of renal function occurs as the external radiation detectors record vascular supply, perfusion, tubular filtration, and excretory phases. A renogram curve is produced as the radionuclide dispersion is plotted on a graph or computed. Comparisons of the right and left kidneys, curve shapes, and relative functions are calculated. Curve shapes are characteristic of certain disorders. This scan uses less radiation than an IVP or CT scan. However, IVP is better for anatomic definition, and arteriography is better for assessment of renal arterial anatomy. Renocystogram is superior to magnetic resonance imaging for medullary renogram evaluation (which must derive medullary information from a mixed study renogram) but equivalent in use for cortical renograms. When the evaluation is being done to identify the presence of renal vascularization abnormalities in hypertension and suspected renal artery stenosis, captopril radiography may be used. For suspected renal artery stenosis only, duplex ultrasound is less costly and invasive and provides similar diagnostic accuracy to captopril radiography.