To retrospectively evaluate the utilization of repetitive kidney stone protocol (KSP) CT scans.

Materials and Methods: This study was approved by our institutional review board, and informed consent was waived. All adult patients at our institution who at least two KSP CT scans for known or suspected urolithiasis between January 1, 2002 and December 31, 2006 were included, and retrospective chart review was performed on a total of 665 patients. The radiology reports for 1,925 KSP CT scans were reviewed for the presence of urinary tract calculi (UTC), specialty type of the referring physician, and patient demographics.

The number of repeated KSP CT scans requested by emergency department physicians was 1,199 (62%) compared with 406 (21%) for urologists, and 320 (17%) for other physicians, with a mean of 2.9 KSP CTs per patient. The mean number of repeat KSP CTs and mean patient ages for the emergency physicians were 2.2 and 42 years, respectively, compared with 1.7 and 49 years respectively for urologists.  For patients receiving 2 to 4 CTs, 4 to 9 CTs, and 10 or more CTs (maximum of 46 CTs), the mean ages were 45 years, 46 years, and 37 years, respectively. A total of 706 (37%) of the KSP CTs showed no evidence of UTC and were considered negative, and 186 (28%) patients had only repeatedly negative results for a total of 491 CTs. Of those patients who never had evidence of UTC, 343 (70%) of the CTs were requested by emergency physicians compared with 40 (8%) by urologists. Some patients (51) initially had negative CTs but had a subsequent CT positive for UTC. A history of 2 consecutively negative KSP CTs had a negative predictive value (NPV) of 83% for the presence of UTC. Similarly, a history of 3 consecutively negative KSP CTs had a NPV of 96%. 

 

Evaluation of patients with known or suspected urolithiasis often results in repeat CTs, with younger patients receiving the most excessive number of repeat CTs, and evaluation in the emergency department resulting in more repeatedly negative CTs compared with other physicians.

A history of consecutively negative CT scans done for evaulation of known or suspected urolithiaisis indicates an extremely low likelihood of current stone disease.