Estimation of Absolute Renal Uptake of 99mTc DMSA in Potential Kidney Donors and its Accuracy in Determination of Split Function

Introduction: Calculation of 99mTc
DMSA split renal function (SRF) is
widely used in daily clinical practice;
however it does not provide information
regarding the functional status of each
kidney separately. Absolute renal uptake
(ARU) is a valuable quantitative
parameter that is capable of assessing the
kidneys’ function independently.
Discrepancies exist in ARU values due to
various quantitative methods used and
standardization of normal ARU values is
probably required at different centers.
Objectives: Establishment of normal
ARU values derived from posterior view
images. Methods: We retrospectively
analyzed 80 healthy adults, potential
kidney donors (64 males, mean age
29.8±8.7 years). All patients had 99mTc
DMSA images. The SRF was calculated
using geometric mean method.The depth
of the kidneys for attenuation corrected
ARU was derived Tonnensen method
(Right kidney = 13.3 (W/H) + 0.7, Left
kidney =13.2 (W/H) + 0.7) as well as from
actual kidney depths on CT. Paired T-test,
Pearson’s correlationand Kappa test were
used to compare different parameters.
Results: The Tonnensen based ARU was
lower compared to the CT based ARU for
left (20.79 ± 4.01% & 24.08 ± 4.50%;
p<0.001) and right kidney (18.79 ± 4.31%
& 23.23±4.9%; p<0.001). Both methods
were highly correlated for left and right
kidneys (r=0.921, p<0.001 & r=0.905;
p<0.001) respectively. The calculated
kidney depths (cm) by the Tonnensen
method compared to the CT were
(6.24±1.03 vs.7.48 ± 1.27; p<0.001) for
left kidney and (6.28±1.04 vs. 8.09±1.42;
p<0.001) for right kidney. Agreement of
posterior view based ARU regarding the
kidney of higher uptake versus that of
geometric mean based SRF, was better for
ARU based on CT depth measurement
compared to that using Tonnensen
equation (Kappa =0.479; p<001 vs.
Kappa= 0.162; p=0.83) respectively.
Conclusions: The ARU calculated based
on Tonnensen method althoughis
underestimated compared to that based on
CT measurement, both are highly
correlated. The variability in normal ARU
values reported in various studies is
probably multifactorial however a key
factor is the method used for kidneysdepth assessment. Consequently it is
recommended that local standardized
reference ARU values be developed by
every nuclear lab rather than using a
predecided values from the literature.