Comparison of Creatinine Based and Kidney Volume Based Methods of Estimating Glomerular Filtration Rates in Potential Living Kidney Donors

Development and validation of risk prediction model for post-donation renal function in living kidney donors

This study aimed to create and validate a predictive model for renal function following live kidney donation, using pre-donation factors. Accurately predicting remaining renal function post live kidney donation is currently insufficient, necessitating an effective assessment tool. A multicenter retrospective study of 2318 live kidney donors from two independent centers (May 2007-December 2019) was conducted. The primary endpoint was the reduction in eGFR to below 60 mL/min/m2 6 months post-donation. The primary endpoint was achieved in 14.4% of the training cohort and 25.8% of the validation cohort. Sex, age, BMI, hypertension, preoperative eGFR, and remnant kidney proportion (RKP) measured by computerized tomography (CT) volumetry were found significant in the univariable analysis. These variables informed a scoring system based on multivariable analysis: sex (male: 1, female: 0), age at operation (< 30: 0, 30-39: 1, 40-59: 2, ≥ 60: 3), preoperative eGFR (≥ 100: 0, 90-99: 2, 80-89: 4, < 80: 5), and RKP (≥ 52%: 0, < 52%: 1). The total score ranged from 0 to 10. The model showed good discrimination for the primary endpoint in both cohorts. The prediction model provides a useful tool for estimating post-donation renal dysfunction risk, factoring in the side of the donated kidney. It offers potential enhancement to pre-donation evaluations.

Predicting new-baseline glomerular filtration rate (NBGFR) after donor nephrectomy: validation of a split renal function (SRF)-based formula

BACKGROUND

Accurate prediction of post-donor nephrectomy (DN) glomerular filtration rate is potentially useful for evaluating and counselling living kidney donors. Currently, there are limited tools to evaluate post-operative new-baseline glomerular filtration rate (NBGFR) in kidney donors. We aim to validate a conceptually simple formula based on split renal function (SRF) previously developed for radical nephrectomy patients.

METHODS

Eighty-three consecutive patients who underwent DN from 2010 to 2016 were included. Pre-operative CT imaging and functional data including pre-DN baseline Global GFR (108.2 ± 13.2 mL/min/1.73m2) were included. Observed NBGFR was defined as the latest eGFR 3-12 months post-DN. SRF, defined as volume of the contralateral non-resected kidney normalised by total volume of kidneys, was determined from pre-operative cross-sectional imaging (49.2 ± 2.36%). The equation derived from Rathi et al. is as detailed: Predicted NBGFR = 1.24 × (Global GFR Pre-DN) x (SRF).

RESULTS

The relationship between predicted NBGFR (66.0 ± 8.29 mL/min/1.73m2) and observed NBGFR (74.9 ± 16.4 mL/min/1.73m2) was assessed by evaluating correlation coefficients, bias, precision, accuracy, and concordance. The new SRF-based formula for NBGFR prediction correlated strongly with observed post-operative NBGFR (Pearson's r = 0.729) demonstrating minimal bias (median difference = 7.190 mL/min/1.73m2) with good accuracy (96.4% within ± 30%, 62.7% within ± 15%) and precision (IQR of bias =  - 0.094 to 16.227).

CONCLUSION

The SRF-based formula was also able to accurately discriminate all but one patient to an NBGFR of > 45 mL/min/1.73m2. We utilised the newly developed SRF-based formula for predicting NBGFR in a living kidney donor population. Counselling of donor post-operative renal outcomes may then be optimised pre-operatively.

Choosing the larger kidney on CT volumetry: a study on the early post-donation kidney function of living donors

BACKGROUND

Selecting the smaller kidney for donation has been advocated if there is a size difference of > 10% between the 2 kidneys but has never been prospectively evaluated. With increase in donor nephrectomies, it is important to evaluate this to minimize loss of renal function to donors.

METHODS

75 consecutive donor nephrectomy patients were included in our longitudinal study. The Split Renal Volume (SRV) of bilateral kidneys were measured using contrasted computer tomography scans and patients segregated into 2 groups depending on donated kidney having more (Group 1) or less than (Group 2) 52.5% of SRV.

RESULTS

Patients in Group 1 (n = 19) and 2 (n = 56) were of similar age (43.8 vs. 48.3), BMI (22.4 vs. 25.2), sex (57.9 vs. 55.4% women), respectively. Although total kidney volumes were similar in both groups, Group 1 had significantly smaller right kidney volumes (120.4 ± 24.9 vs. 142.7 ± 28.4 mls, p = 0.003). EGFR pre-operatively (116.3 ± 20.8 vs. 106.3 ± 23.8 mL/min/1.73 m2) and at 6-months (65.7 ± 13.3 vs. 66.9 ± 15.5 mL/min/1.73 m2) were not different between groups. However, patients in Group 1 had significantly greater absolute (50.6 ± 14.9 vs. 39.5 ± 14.7 mL/min/1.73 m2) and relative decline (43.0 ± 8.6 vs. 36.3 ± 10.6%) in eGFR at 6 months (p = 0.06, 0.009).

CONCLUSION

With a SRV difference of 5% between the 2 sides, removal of the larger kidney for living kidney donation resulted in greater early decline of renal function than kidney donors whose larger or equivalent kidney is preserved.

Renorrhaphy techniques and effect on renal function with robotic partial nephrectomy

PURPOSE

The role of robotic partial nephrectomy (RPN) is becoming increasingly prevalent in managing small renal masses. Renal functional outcomes have been reported with relation to the amount of healthy renal parenchyma resected and ischemia time; however, there is limited data on the effect of renorrhaphy on long-term renal function. Our aim is to evaluate the impact of renorrhaphy technique on renal functional outcomes.

METHODS

A nonsystematic literature review was performed to retrieve articles assessing renorrhaphy techniques and renal function outcomes, specifically focusing on single-layer vs. traditional two-layer renorrhaphy.

RESULTS

Performing single-layer renorrhaphy while omitting cortical renorrhaphy appears to improve renal function postoperatively, based on very limited studies in the literature that were evaluated.

CONCLUSION

Single-layer renorrhaphy may be associated with improved postoperative renal function and could prove to be useful in patients with chronic renal insufficiency or solitary kidney. The ongoing clinical trial NCT02131376 may provide further information on the impact of renorrhaphy technique on long-term renal function.

Visceral obesity in Asian living kidney donors significantly impacts early renal function after donor nephrectomy

INTRODUCTION

Obesity may be a risk factor for kidney donors to develop reduced renal function. The Framingham heart study suggested that visceral adipose tissue (VAT) confers a more adverse metabolic profile compared with subcutaneous adipose tissue (SAT). Asians tend to have a higher VAT composition and it is unclear if their kidney function is affected differently. We hypothesized that Asian living kidney donors who have visceral obesity are at a higher risk of renal function deterioration 1 year after donation.

METHODS

Between 2011 and 2014, we retrospectively evaluated data from 73 consecutive patients (52% male; mean age 44.9 ± 11.7 years) before they underwent donor nephrectomy and at their 1 year routine follow-up. VAT and SAT were measured at the level of the umbilicus on pre-operative computerized tomography (CT). Visceral obesity (VO) was defined as a VAT > 100 cm [2] and patients were then further divided and compared in two subgroups: VAT > 100 and < 100 cm [2]. Estimated glomerular filtration rate (eGFR, mL/min per 1.73 m [2]) was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation pre-operatively and 1 year post-operatively.

RESULTS

Both subgroups had similar baseline kidney function (P = NS) pre-operatively. At the 1 year follow-up, patients with VO experienced a more significant decline of renal function (109 ± 9 to 89 ± 8 mL/min per 1.73 m²), compared to those without VO (111 ± 12 to 96 ± 11 mL/min per 1.73 m², P = 0.013). VO was associated with a body mass index (BMI) > 25 kg/m² (P < 0.001), male gender (P < 0.001) and older age at the time of donor nephrectomy (48.0 vs 39.5 years, P = 0.01). The presence of hypertension or hyperlipidaemia pre-operatively, choice of surgical approach, and post-operative complication rates, did not differ significantly between the subgroups.

CONCLUSIONS

Visceral obesity as defined by VAT > 100 cm² at the level of the umbilicus on cross-sectional imaging, may have a significant impact on early renal function after donor nephrectomy. Adiposity markers, as measured by cross-sectional CT imaging, may be incorporated into routine pre-operative kidney donor workup.

Nephrectomy-induced reduced renal function and the health-related quality of life of living kidney donors

OBJECTIVE

To evaluate the health impact of nephrectomy on living kidney donors (LKDs) by comparing the health-related quality of life (HrQOL) scores measured by Short Form-36 (SF36) between those with and without postdonation renal function impairment (PRFI).

METHODS

Eighty-two LKDs (47 females, mean age=50.2±11.2 years) were prospectively recruited to participate in a SF-36 HrQOL survey. Chart review, individual baseline, and postoperative renal function (eGFR) was determined using the Modification of Diet in Renal Disease formula. PRFI was defined as eGFR<60 mL/min/1.73 m² or proteinuria. Mean SF-36 domain scores were compared between those with and without PRFI.

RESULTS

After a median follow-up of 5.7 years, the prevalence of postdonation comorbidities was 29.3% (n=24) PRFI, 25.6% (n=21) hypertension, 6.1% (n=5) diabetes, and 3.7% (n=3) heart disease, and no LKDs developed end-stage renal disease. Mean eGFR before and after donor nephrectomy was 95.5±23.4 and 71.0±17.3 mL/min/1.73 m² (P<.01). Mean SF-36 scores of LKDs were not significantly different between those with and without PRFI in all the domains (all P>.05). Similarly, the proportion of LKDs with PRFI did not differ significantly between the patients with SF-36 domain scores above and below the published reference values.

CONCLUSION

Nephrectomy-induced PRFI may not have a significant impact on the HrQOL of the LKD population with a low proportion of other major comorbidities such as diabetes and ischemic heart disease.

A semi-automated "blanket" method for renal segmentation from non-contrast T1-weighted MR images

OBJECTIVE

To investigate the precision and accuracy of a new semi-automated method for kidney segmentation from single-breath-hold non-contrast MRI.

MATERIALS AND METHODS

The user draws approximate kidney contours on every tenth slice, focusing on separating adjacent organs from the kidney. The program then performs a sequence of fully automatic steps: contour filling, interpolation, non-uniformity correction, sampling of representative parenchyma signal, and 3D binary morphology. Three independent observers applied the method to images of 40 kidneys ranging in volume from 94.6 to 254.5 cm(3). Manually constructed reference masks were used to assess accuracy.

RESULTS

The volume errors for the three readers were: 4.4% ± 3.0%, 2.9% ± 2.3%, and 3.1% ± 2.7%. The relative discrepancy across readers was 2.5% ± 2.1%. The interactive processing time on average was 1.5 min per kidney.

CONCLUSIONS

Pending further validation, the semi-automated method could be applied for monitoring of renal status using non-contrast MRI.

Preoperative Renal Volume: A Surrogate Measure for Radical Nephrectomy-Induced Chronic Kidney Disease

OBJECTIVES

Surgically induced chronic kidney disease (CKD) has been found to have less impact on survival as well as function when compared to medical causes for CKD. The aim of this study is to evaluate whether preoperative remaining kidney volume correlates with renal function after nephrectomy, which represents an individual's renal reserve before surgically induced CKD.

METHODS

A retrospective review of 75 consecutive patients (29.3% females) who underwent radical nephrectomy (RN) (2000-2010) was performed. Normal side kidney parenchyma, excluding renal vessels and central sinus fat, was manually outlined in each transverse slice of CT image and multiplied by slice thickness to calculate volume. Estimated glomerular filtration rate (eGFR) was determined using the Modification of Diet in Renal Disease equation. CKD is defined as eGFR < 60 mL/min/1.73 m(2).

RESULTS

Mean preoperative normal kidney parenchymal volume (mean age 55 [SD 13] years) is 150.7 (SD 36.4) mL. Over median follow-up of 36 months postsurgery, progression to CKD occurred in 42.6% (n = 32) of patients. On multivariable analysis, preoperative eGFR and preoperative renal volume <144 mL are independent predictors for postoperative CKD. On Kaplan-Meier analysis, median time to reach CKD postnephrectomy is 12.7 (range 0.03-43.66) months for renal volume <144 mL but not achieved if renal volume is >144 mL.

CONCLUSIONS

Normal kidney parenchymal volume and preoperative eGFR are independent predictive factors for postoperative CKD after RN and may represent renal reserve for both surgically and medically induced CKD, respectively. Preoperative remaining kidney volume may be an adjunct representation of renal reserve postsurgery and predict later renal function decline due to perioperative loss of nephrons.

Measurement of renal function in a kidney donor: a comparison of creatinine-based and volume-based GFRs

OBJECTIVE

We aimed to evaluate the performance of various GFR estimates compared with direct measurement of GFR (dGFR). We also sought to create a new formula for volume-based GFR (new-vGFR) using kidney volume determined by CT.

MATERIALS AND METHODS

GFR was measured using creatinine-based methods (MDRD, the Cockcroft-Gault equation, CKD-EPI formula, and the Mayo clinic formula) and the Herts method, which is volume-based (vGFR). We compared performance between GFR estimates and created a new vGFR model by multiple linear regression analysis.

RESULTS

Among the creatinine-based GFR estimates, the MDRD and C-G equations were similarly associated with dGFR (correlation and concordance coefficients of 0.359 and 0.369 and 0.354 and 0.318, respectively). We developed the following new kidney volume-based GFR formula: 217.48-0.39XA + 0.25XW-0.46XH-54.01XsCr + 0.02XV-19.89 (if female) (A = age, W = weight, H = height, sCr = serum creatinine level, V = total kidney volume). The MDRD and CKD-EPI had relatively better accuracy than the other creatinine-based methods (30.7% vs. 32.3% within 10% and 78.0% vs. 73.0% within 30%, respectively). However, the new-vGFR formula had the most accurate results among all of the analyzed methods (37.4% within 10% and 84.6% within 30%).

CONCLUSIONS

The new-vGFR can replace dGFR or creatinine-based GFR for assessing kidney function in donors and healthy individuals.

KEY POINTS

• Accurate prediction of GFR is crucial in kidney donors. • DTPA is accurate but costly, invasive, and clinically difficult to apply. • Volume-based GFR estimation performs as well as the Cr-based method. • New volume-based GFR estimation performs better among GFR estimation formulas.

Feasibility of omitting cortical renorrhaphy during robot-assisted partial nephrectomy: a matched analysis

BACKGROUND AND PURPOSE

To assess the safety of omitting cortical renorrhaphy during robot-assisted partial nephrectomy and measure preliminary functional outcomes.

PATIENTS AND METHODS

Fifteen robot-assisted partial nephrectomies were performed with a running, base-layer suture for the collecting system and vessel hemostasis but without cortical renorrhaphy. The nonrenorrhaphy group was matched 1:2 by R.E.N.A.L. nephrometry score to a running, sliding-clip cortical renorrhaphy group retrospectively. Intraoperative blood loss, urine leaks, postoperative bleeds, and functional outcomes were evaluated. Predictors of %volume loss were evaluated using multivariable regression.

RESULTS

No differences were seen between renorrhaphy and nonrenorrhaphy in sex (P=0.53), age (P=0.14), body mass index (P=0.08), Charlson score (P=0.44), tumor diameter (P=0.55), nephrometry score (P=0.77), preoperative glomerular filtration rate (GFR, P=0.63), or the amount of resected healthy kidney margin (P=0.21). Warm ischemia time was less for the nonrenorrhaphy group (P<0.002). One pseudoaneurysm necessitating embolization (1/30=3%) was seen in the renorrhaphy group compared with none in the nonrenorrhaphy group. No urine leaks occurred in either group. The median %GFR loss was 8.8% for renorrhaphy and 4.4% for nonrenorrhaphy (P=0.14) at a median follow-up of 4.1 months. The median %volume loss was 17 cm(3) for renorrhaphy and 9 cm(3) for nonrenorrhaphy (P=0.003). In a multivariable model, both cortical renorrhaphy (P=0.004) and tumor diameter (P=0.004) were predictors of %volume loss.

CONCLUSION

Omission of cortical renorrhaphy appears feasible with no urine leaks or bleeding complications observed. The percent renal volume loss was improved by omission of cortical renorrhaphy. Reconstruction technique is important to control for when studying renal function after partial nephrectomy.

Optimizing evaluation of split renal function in a living kidney donor using scintigraphy and calculation of the geometric mean: a case report

Within the evaluation process of living kidney donors, split renal function is usually evaluated by renal scintigraphy. Since split renal function measured by conventional posterior scans depends on the position of the kidney, actual suitable donors may be rejected because of an inaccurate examination technique. We report the case of a 28-year-old male living kidney donor. Due to a complex vascular anatomy of the right kidney, only his left kidney was considered eligible for transplantation. In conventional posterior Tc99m-mercapto-acetyltriglycine scintigraphy, the left kidney had a relative function of 60%. A second scintigraphy using anterior and posterior dimercaptosuccinic acid scans with calculation of the geometric mean showed an adapted relative function of the left kidney of 53%, now meeting the inclusion criteria for living kidney donation. This case shows that the geometric mean method using simultaneous anterior and posterior views obtained with a dual-head gamma camera can be a very helpful approach to determine split renal function of potential living kidney donors. Further investigation is necessary to prove the benefit of a general bilateral scan before living kidney donation.