Robustness of estimation of differential renal function in infants and children with unilateral prenatal diagnosis of a hydronephrotic kidney on dynamic renography: How real is the supranormal kidney?
OBJECTIVE
The two methods recommended for estimation of differential renal function (DRF) in the renography guidelines published by the European Association of Nuclear Medicine are the area under the background-subtracted time-activity curves (AUCs) (often called the integral method) and the regression slope of the background-subtracted Rutland/Patlak plot analysis. The current study investigated the agreement/disagreement of DRF estimations obtained using these two techniques. This report also focusses on the occurrence of supranormal function of the affected kidney (defined as DRF >55%) and reviews the related technical and physiological factors.


METHODS
A total of 394 renographic studies in 101 children with a prenatal diagnosis of unilateral renal pelvic dilatation confirmed on postnatal studies were retrieved from optical disc and reprocessed by one author. DRF was calculated using the Rutland/Patlak plot and the AUC over the time period 40-120 s following an injection of( 99m)Tc-mercaptoacetyltriglycine. The difference in DRF between the methods (Rutland/Patlak minus AUC) and 95% limits of agreement were calculated. The age distribution of the difference between the methods was also analysed.


RESULTS
For all 394 measurements the mean difference was -0.8% (range -21.0% to 16.9%, SD 3.9%). The 95% limits of agreement were -7.0% to 8.6%. Analysis of the data revealed that greater spread of DRF between the techniques was seen in studies performed at a younger age: a discrepancy of >5% DRF was significantly more common in those <1 year of age than in those >1 year old (25.3% vs 9.9%; chi-square, p<0.0005). Supranormal function was found less frequently using the Rutland/Patlak method than with the AUC method (8.4% vs 11.2%; chi-square, p<0.0005). The frequency of this diagnosis was reduced to 4.6% when both methods were required to be in agreement.


CONCLUSIONS
The current study supports the existence of age-related variation in the disparity of DRF estimations using the AUC and Rutland/Patlak methods in children with unilateral pelvic dilatation. The close agreement between the AUC and Rutland/Patlak techniques in estimation of DRF in older children supports their use. However, careful quality control of the renogram analysis is essential in young babies. Supranormal renal function (>55% DRF) may in fact be much less common in this group of children than is currently reported.
Ozcan
Zehra
Z
Nuclear Medicine Department of Ege, University Faculty of Medicine, Bornova, Izmir, Turkey.
Anderson
Peter J
PJ
Gordon
Isky
I
D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D006869:Hydronephrosis / Q000000981:diagnostic imaging*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007223:Infant; D007231:Infant, Newborn; D007677:Kidney Function Tests / Q000379:methods*; D008297:Male; D011296:Prenatal Diagnosis / Q000379:methods*; D011866:Radioisotope Renography / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity