## 2 Materials and Methods
### Study Selection and Data Extraction
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Nr.** & **Study** & **Elastography** & **CKD** & **Healthy** & **Kidney** & **CKD vs.** & **Correlation** & **AUROC/Cut-** \\
**Method** & **Patients** & **Subjects** & **SWS in** & **Control** & **Group** & **SWS** & **Off** \\
29. & [PERSON] et al., 2018 [38] & Elast-PQ & 102 & 22 & Low & Yes & \
\begin{tabular}{c} Correlated (but with no statistical \\ performance) \\ \end{tabular} &
\begin{tabular}{c} Performed \\ (CKD vs. \\ control group) \\ \end{tabular} \\ \hline
30. & [PERSON] et al., 2019 [39] & Elast-PQ & 102 & 22 & Low & - & - &
\begin{tabular}{c} Performed \\ (only patients \\ with type 2 diabetes) \\ \end{tabular} \\ \hline
31. & \
\begin{tabular}{c} [PERSON] et al., \\ 2020 [40] \\ \end{tabular} & Elast-PQ & 22 & 103 & High & Yes & Correlated &
\begin{tabular}{c} Performed (non-diabetic, \\ pre-diabetic, \\ diabetic \\ patients) \\ \end{tabular} \\ \hline
32. & \
\begin{tabular}{c} [PERSON] et al., \\ 2021 [41] \\ \end{tabular} & ElastPQ & 75 & - & High & Yes & - &
\begin{tabular}{c} Performed (differentiating \\ between mildly \\ and \\ moderately \\ impaired \\ kidneys) \\ \end{tabular} \\ \hline
33. & \begin{tabular}{c} [PERSON] et al., \\ 2012 [42] \\ \end{tabular} & 2D & \
\begin{tabular}{c} 43 trans- \\ SWE-SSI \\ \end{tabular} & - &
\begin{tabular}{c} No rela- \\ tionship \\ \end{tabular} & - & - & - \\
34. &
\begin{tabular}{c} [PERSON] et al., \\ 2015 [43] \\ \end{tabular} & 2D & SWE-SSI & 25 & 20 & High & Yes & - & Performed \\
35. &
\begin{tabular}{c} [PERSON] \\ et al., 2018 [44] \\ \end{tabular} & 2D-SWE-SSI & 32 & 22 & High & Yes & - & Performed \\ \hline
36. & \
\begin{tabular}{c} [PERSON] et al., \\ 2020 [45] \\ \end{tabular} & 2D-SWE-SSI &
\begin{tabular}{c} 120 \\ idiopathic \\ nephrotic \\ syndrome \\ \end{tabular} & - & High & Yes & - & Performed \\ \hline
37. & [PERSON] et al., 2021 [46] & 2D-SWE-GE & 42 & 50 & Low & Yes & - & Performed \\ \hline \hline \end{tabular}  
* The keywords “high” and “low” refer to a statistically significant change in the KSWV in CKD patients compared to the control group, or in more advanced stages of CKD compared to less advanced stages. (TE = transient elastography, VTQ = virtual touch quantification, SE = strain elastography, RTE = real time elastography, 2D-SWE-SSI/GE = 2D shear wave elastography supersonic image/general electric).  
\end{table} 
Table 1: Cont. We attempted to analyze the 4 studies performed by [PERSON] et al., 2014 [47], [PERSON] et al., 2014 [25], [PERSON] et al., 2015 [26], [PERSON] et al., 2018 [33] performed only on CKD patients (without controls) using VTQ, but unfortunately, the results presented show no correlation between renal function and kidney SWS. [PERSON] et al. (2014) [25] found that the VTQ values of the mild and moderate fibrosis groups were substantially higher than those of the non-fibrosis group, but there was no significant difference between the VTQ values of the mild and moderate fibrosis groups. We also attempted to evaluate the four articles that used the Elast-PQ method, but the data presented were insufficient for statistical analysis. [PERSON] et al., 2020 [40] was the only study that achieved a statistically significant correlation coefficient between eGFR and kidney SWS. Between studies, AUC values are used to compare distinct characteristics (differentiating kidney SWS between mildly and moderately impaired kidneys, between non-diabetic/prediabetic/diabetic patients, or kidney SWS between CKD and control groups), therefore not being suitable for further evaluation. Figure 1: Flowchart of the selection of studies. The “*” from records identified can be deleted. All three studies that used 2D-SWE-SSI reported elevated kidney SWS in patients with CKD; however, only two of them compared CKD to a control group, while the other one performed elastography in patients with idiopathic nephrotic syndrome.