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to qualify as a donor for living kidney transplantation , several preoperative criteria have to be met .
the preoperative evaluation should include blood and urine screening tests , chest x - ray , electrocardiogram , an age- and family history - appropriate cardiac stress test and radiographic assessment of the kidneys and vessels [ 1 , 2 ] .
regarding the selection of the explantation side , vascular anatomy and split renal function are crucial .
the latter is usually evaluated by renal scintigraphy , and there is consensus that the relative function of the donated kidney should not exceed 55% . however , since split renal function may depend on the respective scintigraphy method used , actual suitable donors may be rejected based on inaccurate examination techniques .
we report the case of a 28-year - old healthy male applying to donate a kidney to his 61-year - old father .
the computed tomography ( ct ) angiogram performed showed 2 short renal veins and 2 arteries of the right kidney ( fig .
1 ) . due to the complex anatomy and consequently increased risks for the donor and recipient , a living kidney transplantation of the right kidney was not considered by mutual agreement .
however , the left kidney had a relative function of 60% in conventional posterior tc99m - mercaptoacetyltriglycin ( mag3 ) scintigraphy ( fig .
2 ) , and mag3 total clearance was in the lower normal range ( 242 ml / min/1.73 m ) . considering that the position of the kidney ( e.g. malrotation ) determines the activity measured , a second scintigraphy using anterior and posterior tc99m - dimercaptosuccinic acid ( dmsa ) scans was performed .
as expected , the posterior dmsa scan confirmed the results of the posterior mag3 scan : left kidney 60% . in the additional anterior scan , however , the left kidney now had a relative function of only 46% ( fig .
3 ) . calculating the geometric mean (  a  p ) , the adapted relative function of the left kidney was 53% , now meeting the inclusion criteria for living kidney donation .
confirmatory , ct - based renal cortex volume calculation was almost the same on both sides ( 97.23 and 97.31 ml on the left and right , respectively ) .
after extensive education of the donor and recipient , live donor transplantation was carried out without any intra- or postoperative complications .
postoperative renal function ( egfr ) of the donor was 62.59 ml / min/1.73 m one week after transplantation ( vs. 124.13 ml / min/1.73 m
serum creatinine levels of the donor and recipient were normal at the time of discharge .
six months after transplantation , the egfr of the donor and recipient were 90.75 and 73.64 ml / min/1.73 m , respectively .
to our knowledge , this is the first reported case of a living kidney donor who would have been rejected due to an incorrect result of conventional posterior mag3 scintigraphy .
the influence of left versus right kidney depth variation in renal scintigraphy results has long been understood [ 4 , 5 , 6 , 7 , 8 , 9 ] . if the right and the left kidney lie at different distances from the gamma camera , the ratio of the count rates will not reflect the true relative function because of the different amounts of gamma - ray attenuation .
geometric mean images from combined anterior and posterior views are much less affected by kidney depth and offer the opportunity of more accurate and precise quantification . in 1987 , wujanto et al .  
reviewed 277 dmsa scans and showed that erroneous results were obtained in 32% of patients over 20 years of age when using the posterior view only .
they found a clinically meaningful difference between posterior imaging and the geometric mean method in 55/316 ( 17.4% ) patients over 10 years of age .
although there is consensus that depth correction is not needed in the vast majority of adults , this case shows that using the geometric mean can influence the decision whether to perform a kidney donation . as there is no difference in duration of the examination , costs and radiation exposure between conventional posterior scintigraphy and simultaneous anterior and posterior view , our clinic has adjusted the preliminary assessment of potential living kidney donors : dual scans and calculation of the geometric mean
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 .