Single-Sample Effective Renal Plasma Flow Determination

Objective: There exists a variety of methodologies for the quantitation of effective renal plasma flow (ERPF) with 99"'Tc-MAG3, from very accurate in vitro techniques to less accurate, yet reliable and easy gamma camera methods. This study compares a new technique that uses a single blood sample but does not require the preparation of a standard, with the in vitro single sample ERPF determination (Tauxe). Methods: Thirty ERPF determinations were made by both techniques. One strictly followed the Tauxe methodology. In the second technique, the Tauxe method was modified slightly by deleting the need for standards in the calculation of the theoretical volume of distribution (Vt). In this technique, the dose activity injected was measured in cpm, and the plasma activity concentration was determined in cpm/liter, from which Vt was calculated in order to determine the ERPF. Cesium-137 and Co sealed sources were used for gamma well counter constancy checks. Resuns: There was a significant correlation between the ERPF values from both modalities (r = 0.98, p = 0.012). Conclusion: This simplified technique can be used to reliably determine ERPF, with the accuracy of a plasma sample technique, yet with the simplicity of not requiring standards for each patient.