Renal SWE in CKD: Diagnosis of Parenchymal Fibrosis — Value and Limitations
General Position on Parenchymal SWE
Shear wave elastography (SWE) in the forms of point SWE (pSWE/ElastPQ) and 2D-SWE is based on measuring the propagation speed of shear waves and tissue stiffness. Validated and source-confirmed threshold values pertain to liver parenchyma; validated threshold values for renal parenchymal stiffness for staging fibrosis in CKD do not exist: unlike the liver, renal elastography currently lacks approved diagnostic thresholds (EFSUMB Non-Hepatic Applications, 2018) and is considered an investigational, auxiliary method.
Methodological Principles Extrapolated from Hepatic SWE
According to the EFSUMB Course Book, for point SWE (ElastPQ) reliability, more than 95% of patients achieve 10 valid measurements, with good inter-operator reproducibility noted. In the point SWE (ElastPQ) protocol, a study is considered successful with IQR/Med ≤ 30% (median of 10 measurements).
Value of the Method
According to Diagnostic Ultrasound: Abdomen & Pelvis, the advantages of 2D-SWE include: real-time analysis of shear wave propagation, multiple regions of interest (ROI), and a confidence map, reducing sampling variability. Fibrosis threshold values are device specific and measured in m/s.
Limitations (Critical for Renal Application)
Key limitations of SWE, as noted in the source, directly affect interpretation in CKD:
- Distorting influence of edema, inflammation, and congestion (for the liver — hepatic congestion; edema, inflammation).
- Operator dependency of the method.
- Threshold values depend on the device and method (TE, pSWE/ARFI, 2D-SWE) and specific model.
Since edema and inflammatory changes in the parenchyma are characteristic of CKD, these confounders are particularly significant, and no universally accepted diagnostic stiffness thresholds for the kidneys have been established.
Note on Norms
Stiffness norms depend not only on the manufacturer but also on the method and model of the device. Reference ranges should be checked in the operator's manual of the specific model. Universally accepted SWE reference norms for renal parenchyma have not been established; interpretation should rely on the operator's manual of the specific model and consider the investigational status of the method in nephrology.
Frequently asked questions
Are there validated stiffness thresholds for staging renal fibrosis in CKD?
No. Validated diagnostic stiffness thresholds for renal parenchyma for staging fibrosis in CKD have not been established (unlike the liver); the method is still investigational (EFSUMB Non-Hepatic Applications, 2018).
What factors distort SWE results and are important in CKD?
Edema, inflammation, and congestion, as well as operator dependency of the method — these confounders are particularly significant in CKD.
How many measurements are needed for reliable SWE?
According to the EFSUMB Course Book, for ElastPQ, 10 valid measurements are obtained in more than 95% of patients; the reliability criterion is IQR/Med ≤ 30% (median of 10 measurements).
Do SWE thresholds depend on the device?
Yes, threshold values are device specific — they depend on the method (TE, pSWE/ARFI, 2D-SWE) and model; they are specified in the operator's manual.
What is the practical value of renal SWE then?
As an auxiliary qualitative guide (e.g., increased stiffness in pronounced fibrosis/sclerosis), but not as an independent diagnostic criterion for fibrosis stage — due to the lack of validated thresholds and numerous confounders.