Diagnostic Performance of 99mTc-MAG3 Renal Scintigraphy for Acute Tubular Necrosis and Acute Rejection in Kidney Transplant Recipients with Suspected Graft Dysfunction During the First 90 Days: A Single-Center, Biopsy-Referenced Retrospective Study.

Background

Acute tubular necrosis (ATN) and acute rejection are the principal parenchymal causes of early kidney allograft dysfunction, and biopsy is the reference standard for distinguishing them. We assessed 99mTc-MAG3 scintigraphy against biopsy.

Methods

Single-center retrospective study of transplants (2016 to 2025) scanned within 90 days for suspected graft dysfunction: 42 transplants in 41 recipients, 10% of 420 screened. Accuracy was calculated only in the 25 with a paired biopsy, with exact 95% confidence intervals (CIs). Because biopsy was performed on clinical indication and not in all patients, verification bias was quantified by Begg-Greenes correction and extreme-case bounds.

Results

Scintigraphy was performed a median of 8 days after transplantation; 69% had delayed graft function. Scans were read as ATN in 31 (74%), normal in seven (17%), rejection in three (7%) and obstruction in one; biopsy showed ATN in 15, rejection in six and normal histology in four. For ATN, sensitivity was 14/15 (93.3%; CI 68.1 to 99.8), specificity 7/10 (70.0%; 34.8 to 93.3) and positive predictive value 14/17 (82.4%; 56.6 to 96.2). For rejection, sensitivity was 3/6 (50.0%; 11.8 to 88.2) and specificity 19/19 (100%; 82.4 to 100), the predictive value of three positive scans being uninformative (CI 29.2 to 100). Correcting for verification placed ATN specificity between 29.2% and 76.9% and rejection sensitivity between 13.0% and 50.0%.

Conclusions

Scintigraphy rarely missed biopsy-proven ATN but was not specific and identified only half of the rejection episodes. These estimates rest on small numbers in a clinically selected population; biopsy remains necessary whenever rejection is suspected, and they do not apply to routine or protocol scintigraphy.