Prevalence and clinical importance of alternative causes of symptoms using a renal colic computed tomography protocol in patients with flank or back pain and absence of pyuria.

OBJECTIVES The study was undertaken to determine the prevalence and clinical importance of alternative causes of symptoms discovered in patients undergoing flank pain protocol (FPP) computed tomography (CT) scans in patients with classic symptoms of kidney stone (flank pain, back pain, or both) without evidence of urine infection. METHODS This was a retrospective observational analysis of all adult patients undergoing FPP CT scans at two emergency departments (EDs) between April 2005 and November 2010. All CTs (N = 5,383) were reviewed and categorized as "no cause of symptoms seen on CT," "ureteral stone as cause of symptoms," or "non-kidney stone cause of symptoms." Non-kidney stone scans were further categorized as "acutely important," "follow-up recommended," or "unimportant cause," based on a priori diagnostic classifications. All nonstone causes of pain and a random subset of subjects (n = 1,843; 34%) underwent full record review blinded to CT categorization to determine demographics, whether flank and/or back pain was present, and whether there was objective evidence of pyuria. RESULTS Of all FPP CT scans during the study period, a ureteral stone was found to cause symptoms in 47.7% of CTs, with no cause of symptoms found in 43.3% of CTs. A non-kidney stone diagnosis was found in 9.0% of all CTs, with 6.1% being categorized as "acutely important," 2.2% as "follow-up recommended," and 0.65% with symptoms from an "unimportant cause." In the randomly selected subset undergoing full record review, categorizations were similar, with 49.0% of CTs showing kidney stone as cause of pain and 9.0% a non-kidney stone cause (5.9% "acutely important"). When subjects with evidence of urine infection or without flank or back pain were excluded, ureteral stone was identified as the cause of pain in 54.9% of CTs, while non-kidney stone cause of symptoms was found in 5.4% of scans and acutely important alternate causes in 2.8% of scans. CONCLUSIONS While a non-kidney stone cause for a patient's symptoms are found in nearly 10% of CTs done using a FPP, acutely important findings occur in less than 3% of scans done in patients with flank or back pain and absence of pyuria.