Relative renal function with MAG-3 and DMSA in children with unilateral hydronephrosis

Abstract

Aim: Tc-99m DMSA renal cortical scan is a reference method for determining relative renal function (RRF). Tc-99m MAG-3 is also recommended for the estimation of RRF, particularly in young children. The aims of this study were to compare MAG-3 and DMSA RRF estimations and to assess the reproducibility of these estimations in children with unilateral hydronephrosis.

Methods: We reviewed MAG-3 and DMSA scans of 19 children with unilateral hydronephrosis and a normal contralateral unit. All were imaged with 2 agents within 3 months. MAG-3 RRF was calculated using 2 different time intervals (1-2 and 2-3 min) and perirenal C-type region of background activity. No background correction method was used in the calculation of DMSA RRF. All data were processed twice by two independent operators.

Results: In the repeated estimates of MAG-3 RRF, the maximum mean intra-observer and inter-observer differences were 0.9% (SD 1.7%) and 1.4% (SD 3.3%), respectively. Intra-method analysis showed statistically significant agreement between repeated measures of RRF for two agents as well as for two operators (intra-class cross-correlation coefficients of early and later phase of MAG-3 and DMSA RRF values were 0.979, 0.993 and 0.996 for operator 1, and 0.986, 0.973 and 0.995 for operator 2, respectively; p < 0.001). There were statistically significant correlations between the MAG-3 and DMSA RRF estimations (r = 0.763/0.766 at 1-2 min, 0.835/0.825 at 2-3 min for the repeated measures of RRF for operator 1, and 0.812/0.793 and 0.83/0.89 for operator 2, respectively; p < 0.01, Pearson). Each scan classified as normal or abnormal according to RRF values inter-method analysis showed statistically significant agreement between MAG-3 and DMSA RRF estimations (Kappa statistics). However, there was a slight disagreement between the methods especially in infants and cases with higher grade of hydronephrosis, when 5% difference in estimations and supranormal estimates of RRF were taken into consideration.

Conclusion: Although DMSA and MAG-3 RRF estimations demonstrated a statistically significant correlation with good reproducibility in children with unilateral hydronephrosis, overall the finding of surprising estimates of kidney function with MAG-3 calls attention to the existence of some problems especially in infants and in those with higher grades of hydronephrotic kidneys.