Introduction:

Patients undergoing nephrectomy experience loss of renal volume and diminished overall renal function. Lower pre-operative estimated glomerular filtration rate (eGFR) is a predictor of post-operative chronic kidney disease (CKD) and is a factor in deciding whether to perform partial nephrectomy (PN) or radical nephrectomy (RN). Patients undergoing PN experience less risk of clinically significant CKD and enhanced survival compared to those undergoing RN. Some studies suggest cystatin c may be a more precise and accurate measure with which to calculate eGFR than formulas utilizing serum creatinine. Cystatin C is not dependent on muscle mass and creatinine level making it potentially advantageous in frail cancer patients. The purpose of this study is to evaluate whether Cystatin C and eGFR utilizing cystatin C will correlate more strongly with post-operative renal function as measured by the presence of proteinuria and renal parenchymal volume compared to serum creatinine and creatinine based eGFR.

Methods:

Prospective patients undergoing PN or RN were recruited for this study. Patient demographics were obtained on study enrollment. Patients had laboratory measurements including serum creatinine (SCr), cystatin C (Cys C), and urine studies collected at the pre-operative visit within 30 days of surgery, post-operative day 1 (POD1), and 3-6 months after surgery. Measures of GFR were calculated at each time point utilizing SCr-based formulas, SCr and Cys C-based formulas. Preoperative (within 3 months) and post-operative (3-6 months) abdomen CT or MRI studies were obtained. Slice-O-Matic software (TomoVision, Magog, Canada) was used to construct 3-D measurements estimating renal volume (shown in Figure 1). Pearson’s correlation was used to evaluate relationships between serum measures of SCr, Cys C, calculated eGFR and measures of post-operative renal function (total renal volume, presence of proteinuria, and urine creatinine/microalbumin ratio). Independent samples t-test was used to examine differences in study variables between PN and RN patients.

Results:

The study sample is composed of 43 patients with a mean age of 61.9 years (range 35-89). Thirty-four (79%) patients were male. The race of our sample included: Caucasian (n=25, 58.1%), African-American (n=14, 32.6%), Asian (n=3, 7%), and other (n=1, 2.3%). Twenty-eight patients (65.1%) underwent radical nephrectomy and 15 (34.9%) underwent partial nephrectomy. Serum creatinine at any time point had no significant relationship to measures of post-operative renal function. Serum Cys C measured on POD1 was inversely related to post-operative kidney volume (r = -.36, p = .02).  Calculated eGFR on POD1 utilizing Cys C-based (r=.41, p=.007) and creatinine-based Cockroft-Gault formula (r=.46, p=.002) demonstrated a direct relationship to post-operative kidney volume. There were no differences in the demographic composition of patients undergoing PN compared to RN. Total post-operative renal volume was higher in the PN group (PN: M=358.7 ml, RN: M=239.3 ml) although the difference was not statistically significant (p=.09).

Conclusion:

Cystatin C measured on POD1 as well as eGFR determined by Cys C-based and creatinine-based (Cockroft-Gault) formulas demonstrated a moderate relationship to post-operative total renal volume. Serum creatinine did not demonstrate a significant relationship to post-operative renal volume, presence of proteinuria, or urine creatinine/microalbumin ratio. Cystatin C measured on POD1 as well as eGFR calculated utilizing Cys C and SCr may have some utility in estimating post-surgical renal volume and function compared to POD1 serum creatinine, especially in frail cancer patients with muscle wasting and altered creatinine levels. Further studies are needed to determine the utility of Cys C levels in predicting renal function and risk of renal dysfunction following nephrectomy.

Funding: N/A