Value of the gamma camera renogram in the differential diagnosis of acute tubular necrosis and rejection in the early post-transplant period. Comparison with biopsy findings.

ABSTRACT

A group of 128 consecutive patients was identified on whom renal isotope studies had been performed during the first 2 months after renal transplantation and within 7 days of transplant biopsy. The prospective renogram and biopsy reports were reviewed and graded into 4 categories severe rejection, predominant rejection, predominant acute tubular necrosis (ATN) and pure ATN. Two extreme patterns of renogram were identified a sharp rise with a fast decline in the first min, attributed to ATN, and a slowly rising curve with no early peak occurring in severe rejection although not specific to this condition. There was a continuous intermediate spectrum. There was no inter-observer variation in gradings at the 2 ends of the spectrum. In the middle part the difference between 2 independent observers never exceeded more than 1 grade. There was good correlation between the biopsy and renogram gradings, with a discrepancy of more than 1 grade in only 5 patients; 2 of these, with severe rejection on the renogram, showed predominant ATN on biopsy, but the final clinical diagnosis was severe rejection (false positive biopsies). Two patients with biopsies showing severe rejection had a sharp initial up-slope in the renograms but a slower down-slope (over 4 min compared with 1 min in true ATN). With better definition of the criteria these renograms would not have been graded as ATN. There was 1 patient in whom no satisfactory explanation for the discrepancy was found (presumed false positive renogram). When properly defined criteria are used to interpret renograms, this simple test is at least as reliable as renal biopsy in differentiating ATN from rejection in the early post-transplant period, especially in the presence of anuria or severe oligurea.