Renal ultrasonographic abnormalities are associated with low glomerular filtration rate calculated by scintigraphy in dogs

Abstract

Ultrasound provides information on kidney morphology, but studies relating structural and functional abnormalities in chronic kidney disease (CKD) are lacking. The aim of this descriptive cross‐sectional study was to compare individual kidney (IK) B‐mode ultrasound abnormalities to IK glomerular filtration rate (GFR) estimated by scintigraphy normalized to plasma volume (PV) in dogs, to evaluate if ultrasonographic findings were associated with low IKGFR/PV. Eighty privately owned dogs with and without clinical suspicion of CKD were prospectively enrolled, and kidney ultrasound and IKGFR/PV were evaluated independently. Ultrasound images were assessed retrospectively for subjective abnormalities (shape, cortical, and medullary hyperechogenicity), and kidney size was measured. The normal IKGFR/PV cutoff was derived from dogs in the study group with no history and clinical signs of kidney disease and normal blood and urine results (n = 28) and was 16.84 mL/min/L. Kidneys were categorized into normal, mild, moderate, and severe ultrasound changes according to subjective ultrasound grades. Associations were found between low IKGFR/PV and abnormal kidney shape (P = .0004), cortical hyperechogenicity (P = .0008), medullary hyperechogenicity (P < .0001), and low kidney volume (P = .0092). Apart from the moderate and severe category comparison, IKGFR/PV value significantly decreased with increasing severity of category. The combination of ultrasonographic subjective abnormalities had a high sensitivity (93.8%) and moderate specificity (65.7%) for detecting low IKGFR/PV. Kidneys with normal IKGFR/PV had a low frequency of mild ultrasound changes. Findings indicate kidneys with increasing number and grade of subjective ultrasound abnormalities are more likely to have a lower IKGFR/PV.

How Ultrasound Can Be Useful for Staging Chronic Kidney Disease in Dogs: Ultrasound Findings in 855 Cases

“…Increased cortical echogenicity was also present in dogs with serum creatinine within the reference range, showing that this change may occur in the early stages of the kidney disease in dogs [14]. In the second study, abnormal kidney shape, cortical hyperechogenicity, medullary hyperechogenicity and low kidney volume were found associated with low GFR estimated by scintigraphy normalized to plasma volume [15].…”

“…The degree of renal echogenicity presented a significant positive correlation with serum creatinine and with CKD stage; this correlation was greater than other ultrasound changes considered in the study, such as longitudinal size, parenchymal and cortical thickness [7]. In veterinary medicine, only one study compared renal ultrasound changes with serum creatinine [14], while a recent prospective study compared US abnormalities with GFR calculated by scintigraphy [15]. In the first study, the majority of dogs presented increased diffuse renal cortical echogenicity.…”

Can distinction between the renal cortex and outer medulla on ultrasonography predict estimated glomerular filtration rate in canine chronic kidney diseases?

“…In this study, the RCE was graded according to the distinction of cortex and outer medulla on US images. Several studies attempted to objectively assess the degree of RCE elevation using comparisons to the liver in healthy dogs [ 8 9 ]. However, comparisons with adjacent organs are not objective RCE evaluation methods, especially in clinical patients.…”

“…In addition, most RCE-related studies did not focus only on the cortex, but on echo evaluation in the parenchymal region, including the cortex and outer medulla [ 2 3 8 ]. The renal cortex contains glomerulus, proximal and distal tubules.…”

“…This report concluded that the canine renal cortex on US is actually composed of a true cortex and either an isoechoic or a hyperechoic outer medulla. The authors perceived that RCE evaluation was not evaluated separately from the outer medulla in previous studies [ 1 2 8 9 ]. Therefore, it is assumed that the evaluation of the canine RCE can be more intuitively and objectively compared to the outer medulla than the surrounding organs such as liver or spleen.…”