EVALVATION OF RENAL FUNCTION TEST USING RADIOISOTOPE

Abstract

It is often difficult to follow the postoperative renal function in the urological cases, because urinary stasis, urinary leakage, hematuria and so forth make the test using urine impossible. In these conditions, renal function test using blood instead of urine is desirable. Renal function test using blood serum after intravenous administration of radioisotope was studied.
1) Value of single injection method of radioisotope to observe the changes of postoperative renal function was studied. Several problems were found in the so-called half life method in which the serial serum levels of radioisotope (radiohippuran or radioiothalamate) determine the isotope-disappearance rate which was thought to reveal renal function. It was found that the accuracy of the half life method in clinical use was limited to dividing renal function into only 3 or 4 grades despite rather troublesome technique. This led us to search simpler method of same accuracy.
2) The first trial was to use the ratio of serum concentration of radioisotope at fixed time (40 minutes in Hippuran; 40, 80 and 200 minutes in Iothalamate) after administration to calculated serum concentration at 0 minute. The correlation between this ratio and urinary excretion rate of isotope was poor, probably due to obstructive uropathy of upper urinary tract, individual variation of blood volume, extra-vascular transudation of radioisotope and so forth. But the ratio showed good correlation with 24 hours Ccr which was little influenced by obstructive uropathy.
3) To adjust the individual variation or postoperative change of blood volume and to make the calculation simpler, RHISA was injected with radioactive Hippuran or Iothalamate. And the ratio of
200 minutes' I¹²⁵-RHISA/I¹³¹-Iothalamate (or 40 minutes' I¹²⁵-RHISA/I¹³¹-Hippuran) to
0 minute's I¹²⁵-RHISA/I¹³¹-Iothalamate (or Hippuran) was examined to see its usefulness
as a renal function test. Apparent correlation was found between this ratio and 24 hours Ccr as follows:
200 minutes' I¹²⁵-RHISA/I¹³¹-Iothalamate
-was above 12 when Ccr was above
0 minute's I¹²⁵-RHISA/I¹³¹-Iothalamate
100l/day, and arranged in order between 6 and 12 when Ccr was between 35 and 90l/day. It was 3.12 in two anephric patients under chronic hemodialysis.
40 minutes' I¹²⁵-RHISA/I¹³¹-Hippuran
-was above 6.5 when Ccr was above 100l/day.
0 minute's I¹²⁵-RHISA/I¹³¹-Hippuran
When the ratio was under 6.5, Ccr was under 100l/day. But it was above 6.5 in some cases even if Ccr was between 70 and 100l/day. It was 3.5 in two anephric patients.
4) In some clinical cases, “RHISA/Hippuran” method was used. It was found that this method was simpler and required less time to obtain a result than the so-called half life method, and useful to observe the serial changes of renal function postoperatively or during rejection crisis after renal transplantation. When the period of 40 minutes was not enough to show obvious difference of the “RHISA/Hippuran” ratio because of poor renal function, longer period (80 minutes and 200 minutes) made the difference more distinct and it made it possible to see even the slight change of renal function.