To externally validate the Spectrum Score (SS) using a modified calculation based on functional parenchymal volumes (FPVs) instead of renal scans. The SS quantifies acute ischemic injury in the ipsilateral kidney after partial nephrectomy. However, this metric requires renal split function assessment via renal scans, which may be unavailable in routine practice.

We retrospectively reviewed patients with a solitary renal mass and contralateral kidney who underwent partial nephrectomy at our institution between 2015 and 2017. FPVs were calculated using cylindrical volume approximation and used to quantitate relative renal function. Based on renal split function and parenchyma preserved, we determined creatinine_ideal, assuming no ipsilateral kidney ischemic injury, and creatinine_worst-case, assuming temporary ipsilateral kidney nonfunction. FPV-based SS was defined as follows: (observed peak creatinine−creatinine_ideal)/(creatinine_worst-case−creatinine_ideal). Functional recovery was defined as follows: (% function saved)/(% parenchyma preserved). Factors associated with FPV-based SS and functional recovery were assessed using linear regression.

We assessed 174 patients with a median renal mass size of 2.7cm (IQR 2.0-3.6), warm ischemia time of 26.0 minutes (IQR 19.0-34.3), and parenchyma preservation of 92.6% (IQR 80.8-100). Preoperative ipsilateral kidney % split function (P = .003), preoperative ipsilateral kidney glomerular filtration rate (P = .045), and warm ischemia time (P = .005) were independently associated with FPV-based SS. Only FPV-based SS (P<.001) was independently associated with functional recovery.

The FPV-based SS, which does not require renal scans, quantifies acute ipsilateral renal dysfunction and predicts functional recovery after partial nephrectomy.