Measurement of renal function by calculation of fractional uptake of technetium-99m dimercaptosuccinic acid.

BACKGROUND

The purpose of this study was to set up normal values of the fractional uptake (FU) of technetium-99m dimercaptosuccinic acid in adults and in the pediatric population, as well as to evaluate the validity of this parameter at different levels of renal function.

MATERIAL AND METHODS

A total of 86 subjects was divided into seven groups. In group A there were 23 potential kidney donors and in group B, 18 children in remission after a first urinary tract infection. Another three groups consisted of patients with diabetes i.e. group C, seven patients with normal values of albuminuria, group D, 16 patients with microalbuminuria and group E, five patients with macroalbuminuria. In group F, there were ten patients with a well-functioning transplanted kidney and in group G, seven patients with suspected acute rejection. The procedure began with the quantification of the doses of 99mTc-DMSA to be injected and the measurement of the empty syringe lying on the gamma camera collimator. Thereafter, four planar views of the kidneys were acquired three hours after the injection. The counts from the posterior and anterior views were subtracted for background and corrected for radioactive decay time and patient thickness. The FU was calculated by the geometric mean of counts per second from the posterior and anterior view. It was expressed as a fraction of the injected dose.

RESULTS

The mean values of FU in healthy adults were 0.227 +/- 0.077 for one kidney and 0.454 +/- 0.146 for both kidneys. The mean values of FU for the left and right kidney were 0.225 +/- +/- 0.071 and 0.229 +/- 0.079, respectively. In children, the mean values were 0.220 +/- 0.092 for one kidney and 0.432 +/- 0.094 for both kidneys. The highest values of FU of 0.322 +/- 0.078 (0.644 +/- 0.138 for both kidneys) were measured in group C. In group D, FU was 0.185 +/- 0.065 (0.361 +/- 0.125 for both kidneys) and in group E 0.082 +/- 0.040 (0.163 +/- 0.080 total). In patients with a transplanted kidney, fractional uptake was 0.162 +/- +/- 0.039 in group F and 0.065 +/- 0.021 in group G. There was no significant difference in the values of FU between healthy adults and children. The uptake in group C was 41% higher than in group A and the difference was statistically significant. In groups D and E, the uptake was significantly lower than in A. In both groups of patients with transplanted kidneys, the uptake was significantly lower than in control group. The correlation between FU and biochemical parameters of renal function [blood urea nitrogen (BUN), serum creatinine (Cr) and creatinine clearance (CCr)] was significant: FU/BUN r = -0.86; FU/Cr r = -0.77; FU/CCr r = 0.60.

CONCLUSION

Fractional uptake of 99mTc-DMSA could serve as a sensitive parameter of renal function. The mean values of FU in adults were 0.454 and in children 0.432. There was no significant difference between values for the left and right kidney. In diabetes mellitus, fractional uptake correlated well with the degree of diabetic nephropathy. In patients with a well-functioning transplant, the uptake was slightly reduced. Low values of fractional uptake in acute rejection were related to lesions in kidney blood vessels and in tubular cells.