Calculation of renal differential function following renal transplant: Retrospective validation of a simplified method

OBJECTIVES: The estimation of differential function (DF) in post-renal transplant patients (PRTPs) is challenging because of the different distances of the native kidneys (NKs) and transplant kidney (TK) to the gamma camera and because current commercial software allows evaluation of only 2 kidneys instead of 3. We retrospectively validated a simplified method (SM) to process renal scans and hypothesized that it is comparable with the reference method (RM). PATIENTS AND METHODS: Twelve Tc MAG3 renal scintigraphies of 10 PRTPs were performed on a dual-head gamma camera. The RM was a 2-step process, with the left and right NKs being compared with the TK separately. The SM was a 1-step process combining both NKs together. The DF estimates were consistent with geometric means in both methods. Statistical evaluation included linear correlation and Bland-Altman analysis. RESULTS: The RM and SM showed DF of 78% ± 25% versus 79% ± 27% for the TK and 22% ± 25% versus 21% ± 27% for the NKs (P = 0.3). There was excellent correlation between SM and RM measurements (r = 0.99, P < 0.001). Bland-Altman plot demonstrated a mean difference of 1.2 ± 3.8 at a 95% confidence interval (95% CI) of agreement of -6.2 to + 8.5 for the TK and -1.2 ± 3.8 at a 95% CI of agreement of -8.5 to + 6.2 for the NKs. Only 1 (8%) of 12 scans showed a difference slightly beyond the 95% CI, indicating a good agreement between SM and RM. CONCLUSIONS: The SM offers a simple way to evaluate renal DF in PRTP and shows comparable results with the RM. It may have great potential in clinical practice; however, larger studies are needed to verify and further extend the results of this study.