49 - Correlation between echogenicity of kidneys on ultrasound and eGFR (estimated glomerular filtration rate) in pediatric chronic kidney disease (CKD)

Kidney echogenicity on an ultrasound (US) is determined subjectively as a binary trait by comparing the brightness of the liver to the right kidney.

 

Objective:

Develop a methodology to quantify echogenicity using a readily available software and determine the correlation between cortical echogenicity and eGFR (estimated glomerular filtration rate) in pediatric CKD subjects.

Design/Methods:

This is a retrospective study in a tertiary children hospital. Serial ultrasounds of eight CKD subjects were followed and point ultrasounds for four control subjects were identified with a total of 40 ultrasounds. Three different areas of the kidney cortex and liver were cropped at the similar plane. Using Adobe Photoshop software a gray scale pixel density value was determined. An inverse ratio of the kidney to liver mean pixel densities was the quantified echogenicity index (EI). The kidney lengths as measured by the radiologist were entered into an online calculator (https://www.prevmed.sunysb.edu/jjc/MrNomogram/default2.aspx) to determine the predicted kidney length. The difference between the  mean measured and predicted right and left kidney lengths was the delta length.

Results:

We used the Pearson correlation to show that EI increased as eGFR decreased [r value = -0.65 (p < 0.0001)] depicted in Figure 1. Similarly, the delta kidney length decreased [r value = 0.71 (p value < 0.0001)] shown in Table 1.

The Receive Operating Curve (ROC) analysis curves showed that EI > 0.99 can predict an eGFR< 90 ml/min/1.73m² with a sensitivity of 78% and specificity of 88% whereas an EI > 1.156 can predict an eGFR < 60ml/min/1.73m² with sensitivity of 85% and specificity of 74%, both with an AUC > 0.8.

 

Conclusion(s):

We have developed an easily accessible methodology quantify kidney echogenecity and demonstrate that in CKD patients, as echogenicity index increases the GFR and the kidney size decreases.