131-I hippuran in the evaluation of transplanted kidneys.

Abstract

FOLLOWING A single injection of 131I Hippuran, information regarding the transplanted kidney may be obtained by: (a) radiorenograms; (b) scans of the transplanted kidney and bladder, and (c) the rate of clearance of 131I Hippuran from the blood. The value of the radiorenogram in detecting the rejection of the transplanted kidney by the recipient has been the subject of many papers (1–3). Since August 1967, my associates and I have performed 56 radiorenograms on 36 patients. Analysis of these studies has shown the radio-renogram to be of limited value because of the high incidence of abnormal studies even when there was no clinical or laboratory evidence to suggest dysfunction. Since 1965, we have performed 150 renal scans on 75 patients following injection of 131I Hippuran. The renal scan is helpful in deciding whether or not the kidney is viable, especially in the anuric patient; this technic may also reveal infarcts in the transplanted kidney. Since the scan is not a quantitative study, it is unsuitable for use as a test of renal function; indeed, it may be normal despite severe impairment of renal function and is of limited usefulness in evaluation of possible rejection for this reason. Experimental and clinical studies have shown that the first sign of rejection is a decrease in renal blood flow. Following the injection of 131I Hippuran, renal blood flow can be measured from the formula DV X λ, where DV is the dilution volume and λ is the slope of the curve of clearance of 131I Hippuran from the blood (4–10). The rate of clearance may be measured by an external probe or serial blood sampling. The former method is simple to perform, with good correlation between the values obtained from the two methods (4). In order to estimate the dilution volume, a standard must be prepared. The amount of Hippuran injected into the patient, as well as that used in the preparation of the standard, must be accurately measured. A blood sample must be drawn during the study, usually fifteen minutes after injection, and this must also be counted in the well counting chamber. This portion of the test is rather complicated, and there are many sources of error. Furthermore, such a method of estimating renal blood flow implies functional integrity of the renal tubular cells, and this integrity cannot be presumed to exist in the transplanted kidney. For these reasons, we merely measure the rate of 131I Hippuran clearance from the blood and express this as the T1/2 for blood clearance. The T1/2 for blood clearance of 131I Hippuran is a reflection of renal status. Prolonged T 1/2 values are obtained if there is a decrease in renal blood flow, parenchymal damage in the transplanted kidney, or a combination of the two.