Renal length z-score for the detection of dysfunction in children with solitary functioning kidney

Aim To evaluate whether renal lengthz-scores predict renal dysfunction in children with a solitary functioning kidney (SFK). Methods In a single-centre retrospective cohort of children with SFK, we correlated body mass indexz-scores, extracellular volume and lean body mass to renal lengthz-scores. We grouped thesez-scores to other markers of renal dysfunction (proteinuria, hypertension, extracellular volume and abnormal estimated glomerular function rate [eGFR]) and analysed renal lengthz-score with multivariate analysis, receiver-operated characteristics (ROC) plots and Youden's index to determine an appropriate cut-off. Results 111 children had a median follow-up 5.08 years, eGFR 80.8 mL/min/1.73 m(2), and age at last follow-up 7.4 (3.8-13.4 years). The median renal lengthz-scores of those without any renal dysfunction (n = 37, 25.1%) were greater (+3.66, interquartile range 3.02-4.47) than those with renal dysfunction (median 3.11, interquartile range 1.76-4.11,P = .0107, Mann-Whitney test). Using a cut-off ofz-score of >+1.911, the odds ratio for having no renal dysfunction was 0.07 (95% CI 0.002-0.459,P = .0010). However, accuracy of the renal lengthz-score was poor (ROC curve 0.6488). Conclusion In this cohort of children with SKF, using the renal lengthz-score as a biomarker of renal dysfunction at 7 years of age is not recommended.