Clinicians may be able to use contrast-enhanced ultrasound (CEUS) features to help predict which patients with chronic kidney disease will experience worse outcomes, according to the findings of a prospective study published on August 9 in Ultrasound in Medicine & Biology.
Researchers from Shanghai analyzed which features from CEUS scans were correlated with more severe chronic kidney disease progression in long-term patients. They found derived peak intensity (DPI), in particular, correlated with worse patient outcomes.
"In our study, we found that DPI is a reliable CEUS parameter for evaluating chronic renal changes and an independent prognostic factor of [chronic kidney disease]," wrote the authors, led by Yao Xu from the department of nephrology at Shanghai Jiao Tong University's Renji Hospital.
Cost-effective way to predict progression
Grayscale ultrasound scans are a noninvasive technique to acquire information about kidney health, but they cannot show microcirculation, an important feature for assessing renal function. Similarly, contrast-enhanced CT and MRI can assess renal function, but these modalities have a higher cost and more limitations than ultrasound.
The authors wondered whether CEUS could instead predict chronic kidney disease outcomes by combining the ease and affordability of ultrasound with the more detailed microcirculation information of other contrast-enhanced modalities.
For their study, they enrolled 167 patients who were consecutively hospitalized at the Renji Hospital nephrology department in 2014. The participants were all between the ages of 18 and 80 and had a normal body mass index.
A blinded operator first performed grayscale ultrasound exams on the patients and recorded relevant information, such as echogenicity, renal cortex thickness, and elasticity index. The operator then performed a contrast-enhanced ultrasound exam, noting time-intensity curves, DPI, time to peak, time from peak to one-half, and arrival time.
After their hospital stay, the patients received follow-up exams every three months from doctors at the hospital's nephrology clinic. All patients included in the study had at least six months of subsequent kidney function data, and when available, the authors used up to five years of data in the final analysis.
Out of the 167 participants, 29 experienced chronic kidney disease progression during the five-year follow-up period. Furthermore, 31 patients experienced composite kidney failure events.
A number of ultrasound features were linked to patients with chronic kidney disease progression and poor kidney function. Notably, patients with a lower initial DPI score and thinner cortical thickness had a significantly increased risk of experiencing worse disease progression.
The study results were even more pronounced when researchers stratified patients by their progression status (minimal and mild vs. moderate and severe). They found an inverse relationship between worse severity and renal length and DPI, as well as a positive relationship between worse severity and resistive index.
The authors also created and tested various models that used ultrasound and CEUS features to predict chronic kidney disease progression. A model that combined serum creatinine score with DPI and cortical thickness showed the best prediction abilities, with a sensitivity of 84%, specificity of 73%, and area under the curve of 0.84.
"Our results illustrate the usefulness of DPI as a strong predictor of the progression of chronic changes," the authors wrote.
Why DPI?
DPI, in particular, may be such a stronger predictor of renal outcomes because it is also a predictor of other chronic changes, the authors noted. For instance, DPI indicates perfusion of the organs and was associated with liver and renal changes in animal studies. It was also significantly correlated with the degree of renal fibrosis in study participants.
The authors cautioned that the study didn't take into account any treatments the patients underwent after their hospitalization. Nevertheless, DPI and other ultrasound features look promising as a fast, sensitive tool to predict which patients may have worse renal outcomes.
"This method combines the advantages of tolerability, noninvasiveness, convenience, and suitability for repeated use in routine clinical practice. The DPI can be used as a paid and continuous indicator of renal dysfunction in [chronic kidney disease] patients."
