Imaging of Medical Patients with Acute Kidney Injury: Patterns of Ultrasound Use and the Role of Point-of-care Ultrasound at a Tertiary Care Center

Background

The etiology of acute kidney injury (AKI) can be divided into pre-renal, renal, and post-renal causes. Ultrasound is the test of choice to identify post-renal AKI. While ultrasound is routinely used in the assessment of AKI, obstructive AKI is rare, leading to concerns of potential test overutilization.

Objective

Our primary aim is to describe patterns of use of imaging in patients admitted to hospital with AKI and to determine whether imaging patterns reflect risk of obstruction. Our secondary aim is to identify the role of point-of-care ultrasound (POCUS) when assessing patients with AKI.

Design

This is a retrospective cohort study.

Participants

Patients admitted to internal medicine with AKI over a 12-month period at a large tertiary care academic center.

Main Measures

Our outcome variables were radiology-performed ultrasound, computed tomography (CT), or point-of-care ultrasound (POCUS), presence or absence of hydronephrosis and urological intervention.

Key Results

The proportion of patients with imaging was highest among those with a high-risk score and lowest in patients with a low-risk score (66.0% versus 52.2%). For radiology ultrasound specifically, the rate was 19.5% in low-risk patients and 17.7% in high-risk patients. The prevalence of hydronephrosis among patients at low, moderate and high risk for hydronephrosis was 7.1%, 8.5% and 19.7%, respectively and the rate of urological intervention was 1.4%, 1.2% and 3.8%, respectively. In moderate to high-risk patients, POCUS had a sensitivity of 86.7% and specificity of 90.0% for the identification of hydronephrosis.

Conclusions

In our cohort, nearly 20% of radiology ultrasounds are ordered in patients with a low risk of obstructive uropathy, despite low rates of hydronephrosis and hydronephrosis requiring intervention in this group. With a sensitivity of 86.7% and specificity of 90.0% in patients at moderate to high risk of obstruction, POCUS may support clinical decision making in patients with AKI.