#6853 KIDNEY ELASTOMETRY, KIDNEY MISMATCH INDEX AND CHRONICITY INDEX: NEW METHODS TO INTERROGATE THE DISEASED KIDNEY
Authors: Corte Michele Della , Borriello Gianmarco , Gravina Ilenia , Iulianiello Pietro , Camocardi Andrea , Paglionico Ciro , Matrisciano Rossana , Nappi Felice , Zamboli Pasquale , Viggiano Davide 
Published: June 2023

Abstract

Background and Aims
Standard ultrasound mainly offers information about structural kidney alterations which may provide dates regarding the mass of the filtrating kidney (e.g. the nephron number), or obstructive alterations. Furthermore, the parenchymal Doppler ultrasound offers the resistance index, which is highly correlated to the plasma creatinine levels. However, in conditions of isolated proteinuria with normal kidney function these two classical methods do not reveal any alteration. We have hypothesized that kidney stiffness and a mismatch between creatinine levels and parenchymal resistance indices may offer additional features which may help the nephrologist in the classification of kidney diseases.

Method
In this respect, we have performed a transversal study on 468 patients with available resistance index of both the kidney and the spleen, clinical variables (including hemoglobin, creatinine, cholesterol, proteinuria, hypertension, diabetes) and shearwave elastometry, which gives an estimate of parenchimal stiffness. In order to identify patients with a mismatch between creatinine and renal resistance index we have introduced the kidney mismatch index (KMI) derived from the ratio between the renal resistance index and the creatinine levels. In order to identify chronic patients, we argued that in acute settings the creatinine levels (and hence the resistance index) are altered whereas the kidney size is normal: therefore the ratio of resistance index over the kidney size was tested as a quantitative marker of chronicity.

Results
Results confirm a strong correlation between kidney resistance index and creatinine (Pearson coeff. 0.318, p&lt;0.01). Interestingly, this index is also significantly dependent on age and cholesterol levels using a multiple regression model, after adjusting for creatinine levels. On the contrary, the resistance index of the spleen did not correlate with creatinine or eGFR, whereas it correlated with cholesterol levels. Overall, creatinine levels could be predicted by the kidney size (longitudinal diameter, LD) and by the kidney resistance index (RI) using the following formula: creatinine = 1.8 -0.175*LD + 2.601* RI Conversely, sharewave stifness is only correlated to proteinuria (Pearson coeff. 0.497, p = 0.008) but not with creatinine.Finally, the kidney mismatch index (resistance index dissociated from creatinine levels) does not correlate with proteinuria and seems to identify particular subsets of patients with abnormal microcircle dynamics despite normal filtration rate, and should be tested in future studies as a prognostic factor.

Conclusion
In conclusion, kidney elastometry and kidney mismatch indices may prove additional sources of valuable informations that can be gathered from ultrasound methods which allow the identification of a diseased kidneys even in presence of normal architecture and normal resistance index.