Investigators at Mayo Clinic Arizona have reported new findings in managed care related to renal stone surveillance imaging, originating from Phoenix, Arizona.

According to the research, renal stone surveillance has traditionally relied on ultrasound and radiography of the kidney, ureter, and bladder (KUB) due to concerns about CT radiation exposure and cost — despite CT’s superior diagnostic accuracy. Limited awareness and accessibility of ultra-low-dose (ULD) CT has contributed to its underuse.

Study Objectives and Methods

The aim of the study was to reduce ultrasound use for renal stone monitoring by 30%, with KUB utilization tracked as a secondary measure, without increasing Medicare-allowed amounts. Using the Six Sigma define, measure, analyze, improve, and control framework, a multidisciplinary team analyzed baseline imaging patterns and identified two key drivers of ultrasound and KUB overuse: radiation concerns and lack of awareness and accessibility of ULD CT.

Interventions included incorporating a tin-filter ULD CT protocol and recommending CT for surveillance imaging. Imaging utilization and costs were monitored across three phases: baseline, implementation, and sustained adoption.

Key Findings

Implementation of the ULD CT protocol reduced mean radiation dose by 66% — from 5 mSv to 1.7 mSv — compared with standard low-dose noncontrast CT.

Compared with the baseline period, results during the sustained adoption phase showed:

  • Ultrasound utilization decreased from a median of 35 examinations per month (IQR, 30–36) to 10 examinations per month (IQR, 8.5–18), a 71.4% reduction (P = .002)
  • KUB utilization decreased from a median of 15.0 examinations per month (IQR, 9–19) to 4.0 examinations per month (IQR, 3–5.5) (P = .005)
  • ULD CT utilization increased from a median of 0 examinations per month (IQR, 0–0) to 43.5 examinations per month (IQR, 32.5–58.5) (P < .001)

Cost Implications

The Medicare global fee for a combined ultrasound and KUB was $133.59, compared with $180.82 for ULD CT — an absolute difference of $47.23. This figure does not account for potential additional time and coordination associated with two separate radiology visits required under ultrasound- and KUB-based surveillance.

The researchers concluded that implementing a standardized ULD CT protocol for renal stone surveillance effectively reduced ultrasound and KUB use, with only a modest increase in Medicare-allowed cost. The findings support broader adoption of ULD CT in alignment with updated national guidelines.

This research has been peer-reviewed and published in the Journal of the American College of Radiology. Additional information may be obtained by contacting Maria Zulfiqar, CT Operation Medical Director, Department of Radiology, Mayo Clinic Arizona, Phoenix, Arizona. Co-authors include Katia Ponce, Karen L. Stern, Gene Paden, Kyanna Cusick, Vriddhi Rohila, Mitchell R. Humphreys, Motoyo Yano, and Nelly Tan.

The full study is available through the Journal of the American College of Radiology.