Renal functional reserve in live related kidney donors

A Systematic Review of Renal Functional Reserve in Adult Living Kidney Donors

Introduction

The kidney’s capacity to increase its glomerular filtration rate (GFR) in response to a higher functional demand is known as the renal functional reserve (RFR). Good short-term outcomes after living kidney donation have led to more acceptance of borderline donors (with hypertension, obesity, older age) due the ongoing shortage of donor organs. Given recent concerns about increased long-term risk in some donor subgroups, better donor stratification is needed. Measurement of RFR could inform assessment of donor risk.

Methods

A systematic literature review of studies that assessed RFR in donors pre- and/or post-donation was performed. Given study heterogeneity, descriptive analysis and narrative synthesis was conducted.

Results

Sixteen of 3250 identified studies published between 1956 and 2019 met inclusion criteria. Most studies were cross-sectional and conducted before (n = 8) and/or after (n = 16) kidney donation. Methods for measurement of GFR, effective renal plasma flow (ERPF) and RFR were not standardized. Changes in filtration fraction (FF) and ERPF relative to GFR observed after donation varied depending on stimulus used to induce RFR. Overall, RFR fell after donation; however, over the shorter term, RFR was largely preserved in young healthy donors. RFR was more significantly reduced in donors with hypertension, obesity, or older age.

Conclusion

Existing data suggest possible blunting of RFR post-donation in older, obese, and hypertensive donors, which may represent increased single-nephron GFR at baseline. The long-term implications of these changes deserve further study to determine utility in informing selection of borderline kidney donors.

Renal Functional Reserve Revisited

Kidney function, like the function of other organs, is dynamic and continuously adjusts to changes in the internal environment to maintain homeostasis. The glomerular filtration rate, which serves as the primary index of kidney function in clinical practice, increases in response to various physiological and pathological stressors including oral protein intake. The difference between the glomerular filtration rate in the resting state and at maximum capacity has been termed renal functional reserve (RFR). RFR could provide additional information on kidney health and renal function prognosis. Despite longstanding interest in RFR as a biomarker in nephrology, its underlying mechanisms remain inadequately understood. Moreover, no consensus has been reached on how it should be quantified. Previous studies on RFR have used various measurement methods and yielded heterogeneous results. A standardized and clinically feasible approach to quantifying RFR would allow for more rigorous appraisal of its value as a biomarker and could pave the way for adoption of "renal stress tests" into clinical practice.

Nephrectomy elicits impact of age and BMI on renal hemodynamics: lower postdonation reserve capacity in older or overweight kidney donors

Renal functional reserve could be relevant for the maintenance of renal function after kidney donation. Low-dose dopamine induces renal vasodilation with a rise in glomerular filtration rate (GFR) in healthy subjects and is thought to be a reflection of reserve capacity (RC). Older age and higher body mass index (BMI) may be associated with reduced RC. We therefore investigated RC in 178 consecutive living kidney donors (39% males, age 48 +/- 11 years, BMI 25.5 +/- 4.1). RC was determined as the rise in GFR ((125)I-iothalamate), 4 months before and 2 months after donor nephrectomy. Before donor nephrectomy, GFR was 114 +/- 20 mL/min, with a reduction to 72 +/- 12 mL/min after donor nephrectomy. The dopamine-induced rise in GFR of 11 +/- 10% was reduced to 5 +/- 7% after donor nephrectomy (p < 0.001). Before donor nephrectomy, older age and higher BMI did not affect reserve capacity. After donor nephrectomy, the response of GFR to dopamine independently and negatively correlated with older age and higher BMI. Moreover, postdonation reserve capacity was absent in obese donors. The presence of overweight had more impact on loss of RC in younger donors. In conclusion, donor nephrectomy unmasked an age- and overweight-induced loss of reserve capacity. Younger donors with obesity should be carefully monitored.

Nephrectomy modifies renal angiotensin II effects in kidney donors

BACKGROUND

Age, gender, menopausal status, a family history of hypertension, and renal vascular response to angiotensin II are involved in the progression of renal failure from its very beginning.

METHODS

In order to investigate their importance on this progression, we measured effective renal plasma flow (ERPF) and glomerular filtration rate (GFR), and calculated glomerular pressure (Pglo) and afferent and efferent arteriole resistances (by means of Gomez formulae) in 26 normotensive kidney donors before and after nephrectomy.

RESULTS

Renal reactivity to angiotensin was the only variable that affected changes in renal and glomerular hemodynamics after the loss of renal tissue: in subjects with greater angiotensin reactivity, higher afferent resistances (Ra) and lower glomerular filtration and pressure before nephrectomy change to higher efferent resistances (Re) and higher Pglo and filtration after nephrectomy.

CONCLUSIONS

In normotensive donors with a normal compensatory response to nephrectomy, baseline renal reactivity to angiotensin II can influence renal and glomerular hemodynamics 1 year after nephrectomy.

Routine Screening for the Functional Asymmetry of Potential Kidney Donors

The functional capacity of each kidney of a healthy donor may change under the influence of genetic and environmental factors. An assumption that the donor kidneys show equal function is not always true. As part of the pre-nephrectomy evaluation of potential donors, radioisotope renal scintigraphy using technetium-99m diethylenetriaminepentaacetic acid (99mTcDTPA) was routinely included to evaluate renal functional asymmetry of undetermined etiology. The functional ratios of each kidney using 99mTcDTPA as well as serum creatinine (Scr) and creatinine clearance (Ccr) in a 24-hour urine were measured and calculated from a hundred donors. The left kidneys showed greater function (51.67%-53.35% under 95% confidence interval [CI]) and the average left versus right ratio was 52.5 versus 47.5. The average fraction of Ccr of left kidneys was 57.8 mL/min/1.73 m +/- 10.99 compared with right kidneys at 52.6 mL/min/1.73 m +/- 11.63. Seventy-three healthy volunteers donated their left kidneys, and 27, their right kidney. The average fraction of Ccr of the donated kidneys was 55.9 mL/min/1.73 m +/- 11.78 compared with that of the remnant kidneys (54.5 mL/min/1.73 m +/- 11.39). After kidney donation, the Scr of the donors increased from 0.85 mg/dL +/- 0.17 to 1.33 mg/dL +/- 0.27. The average postnephrectomy Ccr was 68.0 mL/min/1.73 m +/- 14.29. Even though the Ccr after kidney donation was higher than that of the remnant kidney estimated before the donation, one must pay attention to possible functional kidney asymmetry to select the nephrectomy site.

Glomerular function reserve and sodium sensitivity

In clinical nephrology, the glomerular filtration rate (GFR) has been recognized as the golden standard to assess renal function. However, a normal GFR does not necessarily mean normal filtration capability of the kidneys, because impaired filtration capability can be compensated for by elevating glomerular hydraulic pressure. Therefore, an early phase of glomerular dysfunction cannot be detected by the baseline GFR alone. On the other hand, glomerular capillary hypertension is widely recognized as one of the strong risk factors for the progression of nephropathies. Now, it is very important to imagine glomerular hemodynamics in each patient with nephropathy for detecting early dysfunction, as well as for evaluating risk factors. Here, I would like to summarize the current status of how an early phase of renal dysfunction can be detected in clinical practice. I truly anticipate that new methods to assess glomerular hemodynamics in humans will be developed in the near future.

Renal functional reserve in long-term survivors of unilateral Wilms tumor

We hypothesized that long-term survivors of unilateral Wilms tumor would have a decreased renal functional reserve secondary to the consequences of hyperfiltration in the nephrons of the remaining kidney. Therefore we evaluated the renal functional reserve in 12 long-term survivors of Wilms tumor after unilateral nephrectomy (mean +/- SE: 15 +/- 1.1 years; range 9 to 23 years). We measured the creatinine clearance before and after an acute, oral protein load to determine the renal functional reserve. Study subjects and control subjects were matched for age, gender, and body surface area. The basal creatinine clearances were similar (Wilms group 132 +/- 13 vs control group 142 +/- 11 ml/min/1.73 m2; p = not significant (NS]. There was no significant difference in the renal functional reserve between long-term survivors of Wilms tumor and matched control subjects (Wilms group 17 +/- 11 vs control group 25 +/- 11 ml/min/1.73 m2; p = NS). The change in creatinine clearance was not secondary to volume expansion because the fractional excretion of sodium was unchanged with protein loading (Wilms group before loading 0.92 +/- 0.12 vs after loading 0.99 +/- 0.13 (p = NS); control group before loading 0.91 +/- 0.12 vs after loading 1.0 +/- 0.14 (p = NS)). We conclude that up to 15 years after nephrectomy for unilateral Wilms tumor in childhood, there is no evidence of hyperfiltration injury.

Hyperfiltration-induced renal injury in normal man: myth or reality

Current knowledge fails to support the notion that adaptive hyperfiltration of the remnant kidney after donor nephrectomy is deleterious. Rather than being maladaptive, hyperfiltration appropriately compensates for the loss of functional renal mass. Accordingly, most kidney donors can be expected to maintain a stable level of renal function without proteinuria or hypertension. Essential to this is proper selection of donors for nephrectomy and exclusion of high risk potential donors, bearing in mind the fact that apparently healthy, asymptomatic relatives of end stage renal disease patients are prone to the same disease processes that inflict the general population and have a higher risk of underlying renal disease.

Morphological findings in 70 kidneys of living donors for renal transplant

Seventy donor kidneys for transplant were studied with light microscopy (LM), electron microscopy (EM) and immunofluorescence (IM) for C3, C4, Clq, IgG, IgA, IgE, IgM, and antifibrin; the samples were taken just before transplanting the allograft kidney. Glomerular changes were found in 35.7% of apparently normal living donors: 9 cases showed relative glomerular ischemia with an irregular basal membrane (12.9%); 5 cases showed a diffusely widened basal membrane without antecedents of hyperglycemia (7.1%); in one case (1.4%) there was a lesion similar to type 1 mesangio-capillary glomerulonephritis with C3++, IgG++, IgA+, and IgM+; in another case (1.4%) there were scant isolated C3 glomerular, subepithelial deposits with indentation of the basement membrane of the immunocomplex type with a microhematuria which was demonstrated only after donation, and in 9 cases (among them two pairs of siblings) there were mesangial IgA and mesangial electron-dense deposits compatible with Berger's disease (12.9%). None of these glomerulopathies were evident under LM.