Intraobserver and interobserver variations in cortical transit time measurement in children with pelviureteric junction obstruction

Cortical transit time (CTT) has recently been shown to be a useful parameter in the management of children with pelviureteric junction obstruction (PUJO). The aim of this study was to assess intraobserver and interobserver variations in the qualitative and quantitative assessment of CTT in children with PUJO. A retrospective study was performed, and (99m)Tc-MAG3 renogram images of all children with PUJO performed from January 2016 to December 2017 were retrieved. The images were assessed by three observers at two different time points. CTT was qualified as delayed if CTT was more than 3 min else; it was noted as normal. The intraobserver and interobserver variations in the results of the CTT of the normal kidney and affected kidney both before and after surgery were studied. The kappa statistic was used to compare the interobserver variation of qualitative interpretation of CTT. The Bland–Altman plot was used to evaluate the intraobserver and interobserver variations of the quantitative interpretation of CTT. A total of 57 (99m)Tc-MAG3 renal scintigraphies were evaluated. Overall, 114 renal units were evaluated with 51 normal renal units and 63 renal units with PUJO. Of these, 63 renal units with PUJO, 31 renal units had been operated upon, whereas the remaining 32 renal units had no intervention at the time of the study. The kappa statistic in the normal, affected operated, and affected unoperated kidneys was interpreted as almost perfect, substantial to almost perfect, and moderate to substantial level of agreement, respectively. The Bland–Altman plot revealed a large mean difference and wide 95% limits of agreement in affected kidneys (both operated and unoperated). The study concludes that the qualitative CTT interpretation in the affected renal unit which is most commonly used in recent studies is a reliable and reproducible parameter in children with PUJO. The quantitative measurement had wide inter- and intraobserver variation for clinical use.