Radioisotope renography

Radioisotope renography is a form of medical imaging of the kidneys that uses radiolabelling. The two most common radiolabelled pharmaceutical agents used are Tc99m-MAG3 (MAG3 is also called mercaptoacetyltriglycine or mertiatide) and Tc99m-DTPA (diethylenetriaminepentacetate). Some other radiolabelled pharmaceuticals are EC (ethylcysteine) and 131-iodine labelled OIH (ortho-iodohippurate). MAG3 is a better diagnostic agent than Tc-99m-DTPA, particularly in neonates, patients with impaired function, and patients with suspected obstruction. The MAG3 clearance is highly correlated with the effective renal plasma flow (ERPF), and the MAG3 clearance can be used as an independent measure of renal function. After intravenous administration, about 40-50% of the MAG3 in the blood is extracted by the proximal tubules with each pass through the kidneys; the proximal tubules then secrete the MAG3 into the tubular lumen. DTPA is the second most commonly used renal radiopharmaceutical in the United States, primarily because it is the least expensive. Tc-99m-DTPA is filtered by the glomerulus and may be used to measure the glomerular filtration rate (GFR). The extraction fraction of DTPA is approximately 20%, less than half that of MAG3. However, EC is preferred when the serum Creatinine is high.