A PHYSIOLOGICAL APPROACH TO RENAL SCINTIGRAPHY - APPLICATION TO EVALUATION OF HYPERTENSION

The aim of this study was to define the use of the triple radiopharmac eutical renal study (TRRS) for renal scintigraphy as a physiological t ool for renal evaluation, and to determine if the sensitivity and/or s pecificity of a renal study for the diagnosis of renovascular hyperten sion (RVH) could be improved by the combination of three radiopharmace uticals (i.e., 1-131 OIH, Tc-99m DTPA, and Tc-99m glucoheptonate). One hundred ninety-five patients with suspected RVH underwent TRRS, stand ard Tc-99m DTPA renal studies, and renal angiography. One hundred eigh ty-nine patients were hypertensive and ischemic nephropathy was suspec ted in six. Ninety-one, including three patients with ischemic nephrop athy, had a renal artery stenosis of 70% or more (66 unilateral, 25 bi lateral). Effective renal plasma flow (ERPF), glomerular filtration ra te (GFR) (from plasma clearance of 1-131 OIH and Tc-99m DTPA), and geo metric renal masses (from Tc-99m glucoheptonate study) were compared t o normal values corrected for body surface, to determine the severity of renal dysfunction. For the TRSS, RVH criteria included: 1) differen tial Tc-99m DTPA function minus differential Tc-99m glucoheptonate fun ction of affected kidney (< -5% or >5%); and 2) functional parameters: ERPF = 1.6-2.0 ml/g/minute, GFR = 0.25-0.4 ml/g/minute, and filtratio n fraction (i.e., GFR/ERPF = 0.15-0.20) on the affected side. For the standard Tc-99m DTPA renogram, two of the following criteria were used for diagnosis of RVH: time to peak (>5 minutes or a difference of mor e than 1 minute between kidneys), differential uptake (<40%), and cort ical excretion rate (T1/2 > 25 minutes or a difference of more than 5 minutes). The sensitivities of TRRS and standard Tc-99m DTPA were 77% and 68%, respectively, and the specificities were 83.5% and 68%. Sensi tivity was only slightly improved (chi-square test, P < 0.2). However, specificity was significantly higher with TRRS than with standard Tc- 99m DTPA (chi-square test, P < 0.01). The combination of the renograph ic curves and the functional parameters, as done in TRRS, improves sen sitivity and mostly specificity, for the detection of renovascular dis ease. Higher specificity is particularly important in a population wit h a low prevalence of the disease. As exemplified by this study, TRRS can be a noninvasive test to assess renal physiological parameters, fo r clinical and research purposes.