Measurement of Hg203Chlormerodrin Accumulation by the Kidneys for Detection of Unilateral Renal Disease

Abstract

It has long been recognized that a reliable screening procedure is needed for hypertensive patients, in order that a minority whose disease is due to unilateral renal ischemia may be selected. A popular technic for this purpose has been the “radioisotope renogram,” whereby the rate of accumulation and excretion of I¹³¹o-iodohippuric acid², injected intravenously, is measured by paired scintillation detectors external to the kidneys, (3, 4). Since 1959, the mercurial diuretic chlormerodrin (Neohydrin) labeled with Hg²⁰³ has been used for delineation of localized renal lesions by scintillation scanning (2). In addition, renal function may be assessed with this material by measuring its rate of accumulation by a technic similar to the I¹³¹ Hippuran studies. To perform this “chlormerodrin uptake test,” the patient is positioned supine on a modified x-ray table tilted 30° from the horizontal. A preliminary radiograph is obtained for accurate localization of two scintillation detectors under the kidneys. The scintillation crystals (1 3/4 by 2 inches) have flat field collimators extending 8 inches from crystal surface to table top, which restrict the field of sensitivity to a diameter of 5 inches at the plane of the kidneys. Ten to thirty microcuries of Hg²⁰³ chlormerodrin³ are injected intravenously; larger doses of 100 to 150 microcuries are used if scintillation scanning is to be performed subsequently. The count rate from the gamma ray spectrometer and ratemeter of each renal detector is recorded continuously for sixty minutes following injection. The results are expressed as the ratio of the count rate at various times, t, after injection, to the count rate recorded two minutes after injection (Ct/C2). Figure 1A illustrates the mean values of Ct/C2 in 11 selected normal subjects. Figure 1B shows the results obtained in a patient with congenital absence of the left kidney. In Figure 2, the ratios of Ct/C2 of the right kidney to Ct/C2 of the left at various intervals after injection are plotted. The solid line is the mean, plus or minus one standard deviation, of the 11 normal subjects, while the broken lines are studies of 5 patients with unilateral renal disease. After ten minutes, all values in the patients with unilateral renal disease are beyond two standard deviations of the normal values. All but one of these patients were subsequently operated upon for correction of the renal lesion. The rate of chlormerodrin accumulation appears to be a single exponential function, described by the equation Ct = C_∞ (1 - e^kl), where Ct is the count rate over the kidney at time t, C_∞ is the highest count rate reached, and k is the transfer rate constant. The rate of accumulation may therefore be accurately quantitated by either k, the fraction of the dose accumulated per unit time, or by the halftime. In I¹³¹ Hippuran studies, the decrease in radioactivity demonstrated by external renal detectors is primarily a function of the rate of urine flow (1).