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Saudi Journal of Kidney Diseases and Transplantation
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LETTER TO THE EDITOR Table of Contents   
Year : 2010  |  Volume : 21  |  Issue : 2  |  Page : 350-353
Is the omission of assessing split renal function from living kidney donor's work-up justified?


Consultant Nephrologist, King Fahad Specialist Hospital, P.O. Box 15215, Dammam, Saudi Arabia

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Date of Web Publication9-Mar-2010
 

How to cite this article:
Abutaleb N. Is the omission of assessing split renal function from living kidney donor's work-up justified?. Saudi J Kidney Dis Transpl 2010;21:350-3

How to cite this URL:
Abutaleb N. Is the omission of assessing split renal function from living kidney donor's work-up justified?. Saudi J Kidney Dis Transpl [serial online] 2010 [cited 2019 Nov 21];21:350-3. Available from: http://www.sjkdt.org/text.asp?2010/21/2/350/60211
To the Editor,

Assessing split renal function by renal scan is being increasingly omitted, from the transplant donor work-up tests in many transplant centers. This is apparently based on the assumption that the gross symmetry of the renal anatomy (size) and function as depicted by ultrasound and/or excretory phase of computerized tomo­graphy (CT) angiography is sufficient to avoid missing clinically significant renal functional/ anatomical asymmetry.

I propose here, that accepting gross symmetry between the two donor's kidneys as suggested by the commonly available test parameters as ultrasonic kidneys' length is not consistent with the accepted attitude of prioritizing donors' needs and concerns. As would be discussed below, other advanced tests such as spiral CT angiography and MRI, do not seem satisfac­tory in this regard. The significance of dispa­rity in renal length is difficult to define. In face of other factors, tolerance toward apparently minor renal length differences is usual among transplant physicians. In these occasions, the choice of the kidney to be removed would mostly be left for surgical preferences that in­clude the anatomy of the renal vasculature of each kidney. Factors such as length of the re­nal vein (favoring choosing the left kidney) and multiplicity of renal vessels became essen­tially the sole factors on deciding which kid­ney to remove. In fact, some transplant teams, in favor of getting the left kidney with its longer vein, have apparently dropped the factor of ve­ssel multiplicity on almost a routine basis. Santiago Horgan et al [5] reported that the left kidney is routinely chosen in their center, re­gardless of the presence of anatomical varia­tions. They utilize spiral 3-dimensional CT scan to assess renal parenchyma, vascular anatomy, and the collecting system. No comments were made, however, on the CT measurement of re­nal volume or on the degree of renal size/func­tion asymmetry that would justify altering their routine choice of left kidney. Such attitude of choosing the left kidney on a routine basis with­out assessment of split renal function or vo­lume seems to be increasing among transplant centers. [6],[7],[9] Emamian SA et al studied kidney dimensions in 665 healthy volunteers and re­ported median renal volume of the left and right kidneys to be 146 and 134 mL, respectively. Comparable median renal lengths were 11.2 and 10.9 cm, respectively. The difference bet­ween the two sides was statistically significant in all age-groups. [7] One might note from these values how exaggerated the disparity at the volume level is, relative to that at length level. In fact, a difference in length of above three mm indicates a length ratio of 0.97. Assuming that the other two dimensions have the same ratio, then the volume ratio would be 0.91, which would be translated into 12 to 13 mL volume difference as reported by the authors above. An association between kidney length and width and surface area has been in fact, documented earlier. [6] So, in the absence of split renal function or volume, how much of the length disparity, for the sake of smoother sur­geries, can we tolerate? Moreover, the magni­tude of such volume/function disparities would be inflated by a factor of two-fold, when rela­ted to the nephron mass that would actually be left to the donor. To clarify this further, if the lengths of both kidneys were 11 +/- 0.5 cm (i.e. the length ratio of 0.913), then a 24% disparity in renal volume can be expected. The nephron mass distribution between the two sides, in this example, would be 38% vs. 62%. This simply means that donating the larger kidney, would leave the donor with a total nephron mass that is less by 48% from that which would have been left for him if the smaller kidney was the one donated. Do we have the right to ignore the donor side on deciding to tolerate the +/­0.5 cm length differences?

Based on studying a control group of 100 potential donors, Shokeir AA et al found the mean disparity of renal functional to equal 6 mL/min (5.31% of total GFR). They considered renal disparity greater than the mean as signi­ficant. When this definition was applied to another subsequent study group of 200 poten­tial donors, these authors found a total of 84 donors (42%) with significant disparity. In all these donors, the kidney with lesser function was chosen for nephrectomy regardless of ana­tomical considerations such as multiplicity of renal arteries. Obviously, this level of functio­nal disparity (5.3% or alternatively expressed as +/- 2.7% difference between the two sides) is unlikely to be consistently reflected on ultra­sound estimated renal lengths.

Recently, spiral computed tomographic angio­graphy (CTA) has become a standard method of pre-operative evaluation of potential kidney donors. The accuracy of the test to visualize renal vasculature anatomy has been documen­ted repeatedly. [1],[3] The test has replaced both IVP and the invasive renal angiography in most centers. Estimation of the kidneys' volume by CTA is also possible, especially by utilizing multidetector CT (MDCT). Relative renal vo­lume is likely to reflect the distribution of the total nephron mass and so the relative function of the two kidneys. CT calculated volumes are expected to be more accurate than ultrasound­estimated renal lengths or volumes. However, the MDCT is poorly utilized or looked at, to calculate renal volumes. Additionally, the accu­racy of CT to predict renal volumes seems sub­optimal. In their prospective study about the accuracy of the 3-D CTA prior to living donor nephrectomies, Janoff Daniel M et al [1] reported a coefficient of variation index (how much average CT volume differed from measured intra-operative volume) of 17.8% for volume prediction. They concluded that volume com­parisons might be inaccurate when the diffe­rence in kidney volume is within 17.8%. Again, such ignored difference can mean an extra 35.6% nehron mass for the donor, if his best kidney is left for him. Similar failure of the usefulness of the 3 D CT as a tool for pre­operative kidney selection for donation was also reported by C.T. Wu et al. [4] Although MRI­derived kidney volume evaluation was consi­dered more accurate than comparable ultra­sound-derived evaluation, [8] several authors have found 3D CT more accurate than MRI, at least for defining renal vascular anatomy. [1],[3] Thus, it seems unlikely that MRI-derived volume values would be more accurate than those of 3D CT. Failure of obtaining accurate pre-operative re­lative renal volume by these tests justify sticking to the old approach of direct assess­ment of the split renal function (rather than anatomical parameters) through isotope renal scans. Earlier attempts to calculate split renal function (not volume) directly from contrast enhanced CT examination seems providing a practical alternative for renal scans in the kid­ney donor work-up. That is because such CTA test is already an essential compo-nent of the donor work up. This approach is based on the assumption that contrast medium accumula­tion is proportional to the renal function. Some authors have accepted CT estimated split renal function as an alternative to renogram. [12] This conclusion was, however, reached despite the finding that the correlation between CT and renography was just moderate (r= 0.43). Henrik Bjorkman [11] reported that earlier attempts, how­ever, did not seem successful. The approach he introduced for improving the accuracy of CTA- calculated split renal function seems promi­sing, but would need further confirmation.

Regardless of all the reassuring reports about the safety of kidney donation, I would believe that ignoring disparities in renal length and volume is unfair to the donors, who trusted our judgment to prioritize their rights. It could prove a breach for the exhortation "First, do no harm". Many of our accepted donors have in fact, other relative contraindications such as obesity, mild hypertension and smoking that have been ignored. In addition, available do­nor data (retrospective) are not complete from studies on white population. Extrapolation to black population may not be completely appro­priate given the fact that nephron under dose seems already responsible for the higher pre­valence of hyper-tension (41% vs. 28%) [16] and the higher risk of ESRD in this population (six­fold greater). [17] Thus, tolerance of uni-nephrec­tomy may not be similar in blacks with low baseline GFR and presence of other co-exis­ting risk factors.In addition, it has been found that the relative risk of ESRD increases by a factor of 2.28 if the donor pre-nephrectomy GFR was < 80 mL/ min. [19] Until proved other­wise, such data points to the importance of do­nor residual renal function. As expected, graft survival was also found poorer with donor base­line GFR < 80 mL/min. These data stress the importance of accurate pre-operative assessment of total GFR. Renal scan fulfills this require­ment most efficiently. Many donors are being placed into CKD stage 3a or even 3b. Data from general population suggests significant morbi­dity and mortality associated with such CKD stage. A 5-year mortality of 24.3% was re­ported among general CKD stage 3 cohorts by Keith et al. [15]

There should be no doubt that leaving the kidney with higher volume/better function is advantageous for the donor. It is unfair with our donors to ignore above clues and request a more definite proof for this basic assumption in order to adopt it! Rather, the appropriate atti­tude of nephrologists should continue to assess split renal function and fight to keep for the donors their best kidneys unless the two sides' differences are truly minor!

The main argument against this discussion is that the short and long-term outcomes of living kidney donors are excellent. The risk of deve­lopment of ESRD among kidney donors is just 0.2 to 0.5%; with significant proteinuria (> 1gm/day) in only 3 to 19% .[2] The role of "nephron under-dosing" in some of the donors does not seem significant, given the presence of many other co-existing factors that would, potentially, predispose the donors to renal failure. An inter­mediate-term elderly donor follow-up study pro­vided reassuring data; the GFR was found to be 37.2 ± 11.2 and 37.3 ± 10.7 mL/min. at one year and last follow-up visits (average follow up was 57.4 ± 4.3 months). [13] Similarly, R. Saran et al [14] reported gross stability of GFR among 47 renal transplant patients over 10-years follow­up (1984-1994). These reassuring long-term follow-up studies, however, are retrospective in nature with generally low retrieval (inclusion) rates. Elizabeth SO et al summarized results of 25 short to long-term studies on renal donors and noted that the majority have a participa­tion rate of 80%, and seven have lower than a 50% participation rate. [18]

In conclusion, I believe that no effort should be spared to protect the donors' right in main­taining highest possible residual renal reserve. This can only be reached through continuing to assess donor split renal function by either radioisotope or CT tests.

 
   References Top

1.Patrick D, James H, Lemmers MJ, Paduch DA, Bbarry JM. Computerized tomography with 3­dimensional reconstruction for the evaluation of renal size and arterial anatomy in the living kidney donor. J Urol 2004;171:27-30.  Back to cited text no. 1      
2.Sommerer C, Morath C, Andrassy J, Zeier M. The long-term consequences of living-related or unrelated kidney donation. Nephrol Dial Transplant 2004;19:IV45-7.  Back to cited text no. 2  [PUBMED]    
3.Bhatti AA, Chugtal A, Haslam P, Talbot D, Rix DA, Soomro NA. Prospective study com­paring three-dimensional computed tomogra­phy and magnetic resonance imaging for eva­luating the renal vascular anatomy in potential living renal donors. BJU Int 2005;96(7):1105-8.  Back to cited text no. 3      
4.Wu CT, Liu KL, Chu SH, Chiang YJ. Pre­operative evaluation of living related kidney donor: Which kidney to donate? Transplant Proc 2006;38:1980-1.  Back to cited text no. 4  [PUBMED]    
5.Horgan S, Benedetti E, Moser F. Robotically assisted donor nephrectomy for kidney trans­plantation. Am J Surg 2004;188(Suppl):45S­51S.  Back to cited text no. 5      
6.Fernandes MM, Lemos CC, Lopes GS, et al. Normal renal dimensions in a specific popu­lation. Int Braz J Urol 2002;28(6):510-5.  Back to cited text no. 6      
7.Emamian SA, Nielsen MB, Pedersen JF, Ytte L. Kidney dimensions at sonography: Correla­tion with age, sex, and habitus in 665 adult volunteers. AJR Am J Roentgenol 1993;160 (1):83-6.  Back to cited text no. 7      
8.Cheong B, Muthupillai R, Rubin MF, Flamm SD. Normal values for renal length and vo­lume as measured by magnetic resonance ima­ging. Clin J Am Soc Nephrol 2007;2:38-45.  Back to cited text no. 8  [PUBMED]    
9.Yaraghi HM. Sonographic measurement of absolute and relative renal length in healthy isfahani adults. J Res Med Sci 2004;2:1-4.  Back to cited text no. 9      
10.Fehrman-Ekholm I, Elinder C, Stenbeck M, Tyden G, Groth C. Kidney donors live longer. Transplantation 1997;64(7):976-8.  Back to cited text no. 10      
11.BjOrkman H. Alternative methods for assess­ment of split renal function. Acta Universi­tatis Upsaliensis. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine 319. 76 pp. Uppsala. ISBN 978-91-554-7121-7  Back to cited text no. 11      
12.Nilsson H, Wadstrom J, Andersson L, et al, Measuring split renal function in renal donors: Can computed tomography replace renography? Acta Radiol 2004;45(4):474-80.  Back to cited text no. 12      
13.Kumar A, Verma BS, Srivastava A, Bhandari M, Gupta A, Sharma RK. Long-term follow up of elderly donors in a live related renal trans­plant program. J Urol 2000;163(6):1654-8.  Back to cited text no. 13      
14.Saran R, Marshall SM, Madsen R, Keavey P, Tapson JS. Long-term follow-up of kidney donors: A longitudinal study. Nephrol Dial Transplant 1997;12:1615-21.  Back to cited text no. 14  [PUBMED]    
15.Keith DS, Nichols GA, Gullion CM, Brown JB, Smith DH. Longitudinal follow-up and out­comes among a population with chronic kid­ney disease in a large managed care organi­zation. Arch Intern Med 2004;164(6):659-63.  Back to cited text no. 15      
16.Hertz RP, Unger AN, Cornell JA, Saunders E. Racial disparities in hypertension prevalence, awareness, and management. Arch Intern Med 2005;165:2098-104.  Back to cited text no. 16  [PUBMED]    
17.Bergman S, Key BO, Kirk KA, Warnock DG, Rostant SG. Kidney disease in the first-degree relatives of African-Americans with hypertens­ive end-stage renal disease. Am J Kidney Dis 1996;27:341-6.  Back to cited text no. 17  [PUBMED]    
18.Ommen ES, Winston JA, Murphy B. Medical risks in living kidney donors: Absence of proof is not proof of absence. Clin J Am Soc Nephrol 2006;1:885-95.  Back to cited text no. 18  [PUBMED]    
19.Norden G, Lennerling A, Nyberg G. Low absolute glomerular filtration rate in the living kidney donor: A risk factor for graft loss. Transplantation 2000;70(9):1360-2.  Back to cited text no. 19      

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Correspondence Address:
Nasrulla Abutaleb
Consultant Nephrologist, King Fahad Specialist Hospital, P.O. Box 15215, Dammam
Saudi Arabia
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PMID: 20228530

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