Introduction:ARFI elastography is very useful for liver stiffness assessment, but few information are available regarding
kidney stiffness (KS), especially in non-transplanted kidney.
Aim: to assess the KS by means of ARFI elastography, in subjects without kidney pathology (“normal” subjects) and to identify the factors which influence it.
Methods:Our study included 91“normal” subjects: 33 healthy volunteers (36.3%), without known kidney pathology, with normal renal ultrasonography, without history of renal disease (supplementary investigations were not performed in these subjects) and
58 patients hospitalized (63.7%), for various diseases, with normal renal ultrasonography, normal serum creatinine and blood urea nitrogen and without proteinuria or hematuria. We aimed for five valid ARFI measurements, which were performed in the mid-portion of the parenchyma, in each kidney, with the subjects in left or right lateral decubitus; median values were calculated and expressed in meters/second (m/s).
Results: Five valid ARFI elastographic measurements were obtained in all “normal” subjects in both kidneys. The mean KS values obtained in the right and left kidney were similar: 2.49 ± 0.81 m/s vs. 2.36 ± 0.75, p=0.25. Since the KS values were similar in both kidneys, further analyses were made for KS values obtained in the right kidney. In univariant analysis, age (r= -0.370, p=0.003), gender: female vs. male (r = -0.305, p=0.003) and measurement depth (r = -0.285, p=0.01) were significantly correlated with KS
values assessed by ARFI elastography, while body mass index (r= -0.127, p=0.23), kidney length (r=0.026, p=0.80) and renal cortex thickness (r= -0.151, p=0.15) were not correlated. In multivariate analysis, only age (p=0.006) and gender (p=0.03), were significantly correlated with KS values. The mean KS values (m/s) assessed by ARFI elastography were significantly lower in men as compared with women: 2.22 ±0.76 vs. 2.70 ± 0.80, p=0.004. The mean KS values (m/s) decreased with age, as follows: 18-30 years = 2.94 ± 0.60 , 31-50 years = 2.26 ± 0.82, 51-65 years =2.48 ± 0.82 and older than 65 years = 1.82± 0.63.
Conclusion:KS values assessed by ARFI elastography in “normal” subjects are influenced mainly by age and gender and less by depth of measurement.
