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.