Objectified kidney ultrasound echogenicity and size metrics as potential predictors for kidney function in children

Kidney echogenicity is typically determined subjectively but may have a quantifiable relationship to kidney function. Similarly, kidney length has been shown to correlate with kidney function. This study sought to quantify echogenicity using readily available software. Secondarily, we aimed to evaluate the correlation between quantified echogenicity and kidney length to the estimated glomerular filtration rate (eGFR) in children with acute kidney injury (AKI) and chronic kidney disease (CKD).

In a single-center retrospective observational study, echogenicity index (EI) was determined using a ratio of right kidney to liver mean pixel density. The kidney length ratio (KLR) was determined by the actual to predicted lengths of both kidneys. Both variables were correlated to eGFR using correlation analyses and predictive capacity was determined with receiver operating characteristic curve (ROC) analysis.

Of 94 subjects, 46% (43/94) had AKI, 28% (26/95) had CKD and 26% (25/95) were controls. The higher the EI the lower the eGFR (r = - 0.46, p < 0.0001). EI between 1.0 and 1.1 predicted an eGFR < 90 ml/min/1.73m² with an AUC of 0.71-0.78 while an EI between 1.1 and 1.2 predicted an eGFR < 60 ml/min/1.73m² with AUC of 0.75-0.80. Overall, the larger the KLR the lower the eGFR (r = - 0.25, p 0.018).

We have developed an accessible methodology to quantify kidney echogenicity. Overall, there was an inverse correlation between EI and eGFR in pediatric CKD and AKI. However, these correlations did not persist within subgroups which could be due to small sample size and heterogeneity of etiologies. Overall, KLR had a weaker correlation to eGFR, compared to EI. Despite these correlations, both EI and KLR had "fair" to "good" performance as a biomarker for an eGFR < 60 ml/min/1.73m².