Hilson index and renal transplant rejection: a single-center experience
Muhammad Choudhry, Nitesh Rao
Department of Renal Medicine, Royal Adelaide Hospital, Adelaide, SA, Australia
Background: The Hilson index has been used in addition to sequential images and changes in posttransplant region-of-interest curves to separate rejections from acute tubular necrosis. The aim of the present retrospective study was to evaluate the role of the Hilson index in accurately diagnosing renal transplant rejection and to explore the correlation between changes in the perfusion index across serial scans with the incidence of rejection.
Methods: Using the Hilson index, we retrospectively examined 150 renal biopsies and 250 perfusion scans from 150 renal transplant recipients from 2010 to 2012 at our center. A Hilson index above 150 was labeled as positive and anything less as negative. Renal transplant rejection was diagnosed by correlating clinical suspicion with the histological findings of the renal biopsy. The Hilson index closest to the perfusion scan and the histology findings on renal biopsy were used to calculate the sensitivity and specificity of the index in diagnosing renal transplant rejection. Logistical regression was used to determine the relationship between absolute and percentage changes in perfusion scan indices with histological findings.
Results: The Hilson index had a sensitivity of 26% and a specificity of 82% in predicting renal transplant rejection. The Hilson index was not specific in differentiating between acute tubular necrosis and renal rejection. The absolute and percentage changes in value of the index did not correlate with renal transplant rejection.
Conclusion: At our center, the Hilson index had poor sensitivity for diagnosing renal transplant rejection. The absolute and percentage changes in the Hilson index across serial scans failed to correlate with renal transplant rejection. The findings of this audit suggest the need for individual clinical discretion and the use of the Hilson index as supportive information only. This has raised interest in utilizing resistive indices from renal ultrasound for this purpose at our center. The sensitivity and specificity of Doppler ultrasound have been inconsistent and observer-dependent in various studies. Magnetic resonance imaging has been proposed but is unrealistic. Due to the nature of the test and its results, an audit cycle was not considered plausible.
Keywords: Hilson index, renal transplant rejection, acute tubular necrosis
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