Radionuclide clearance techniques

A review of methods used in performing radionuclide renal clearance is presented. Adequate radionuclide substitutes for inulin and paraaminohippurate (PAH) have made possible a variety of techniques for measuring glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). The major deterrents to the standard inulin and PAH clearance procedures, including difficult chemical determinations, continuous intravenous infusions, timed catheterized urine collections, and frequent blood sampling, have been varyingly eliminated by the newer radionuclide clearance techniques: chemical determinations are replaced by simple gamma counting; the need for continuous infusions is obviated by the ability to quantitate gamma activity at very high and very low concentrations; urine collections can be eliminated by the analysis of plasma disappearance or by measuring the infusion rate necessary to maintain a constant plasma level; frequent blood sampling can be minimized by external gamma monitoring or by utilizing established volumes of distribution and inter-compartmental clearance based on patient studies. An attempt is made to present superficially the basic concepts used in analyzing plasma disappearance after a single intravenous injection. Mathematical derivations are not presented in depth, although some considerations of the two-compartment system are given in the Appendix. Although there are few disadvantages in using the newer radionuclide techniques compared with the standard infusion methods, direction from an individual with a firm foundation and genuine interest in renal physiology is paramount in establishing these procedures as acceptable and reproducible substitutes for measuring GFR and ERPF.