n patients with acute or progressive azotemia, a renal sonographic examination is usually requested to look for a postrenal obstructive cause. This is because in addition to being a noninvasive, portable, and relatively low-cost examination, sonography has a reported sensitivity of up to 98% for detecting renal obstruction.1 Nevertheless, because obstructive uropathy is lacking in most azotemic patients, is it really necessary and practical to do a sonographic examination in any and all patients with acute or progressive renal failure? This important question is addressed by Keyserling and associates,2 who in this issue of Journal of Ultrasound in Medicine evaluate the efficacy of renal sonography performed on patients in intensive care units with acute or acute-on-chronic renal failure. These authors evaluated 104 azotemic adult patients in an intensive care unit without clinical signs and symptoms of obstructive uropathy and discovered that only 1 patient had mild hydronephrosis, and in that case, it was not considered the cause of the renal insufficiency.2 Based on current Medicare reimbursement, the total cost for doing studies on these patients was calculated as greater than $13,000. The conclusion reached by these investigators was that because the diagnostic yield to exclude hydronephrosis in azotemic patients in intensive care units without predisposing causes for obstructive uropathy was so low, this examination is unnecessary. Additionally, because this is an economically wasteful study, it results in unnecessary cost to patients and to hospitals. These results parallel those of a previous report that evaluated the diagnostic yield of sonography in the evaluation of azotemic patients.3 In that study, the investigators divided the total patient population of 394 azotemic patients into 2 groups. One group included 119 patients considered at high risk for obstructive uropathy, and the remaining 275 patients were considered at low risk for obstructive uropathy. In the high-risk group, 35 patients (29%) were found to have postrenal urinary obstruction due to known pelvic malignancy, a palpable abdominal or pelvic mass, suspected or known calculus disease, bladder outlet obstruction, recent pelvic surgery, or suspected renal sepsis. Based on their cost calculation of $258 per sonographic study, the cost per case of hydronephrosis in the high-risk group was calculated as $877. In the low-risk group of patients, there were 2 cases of hydronephrosis (1%), and based on a similar fiscal calculation, the cost per case of hydronephrosis in this group was calculated as $23,650. Both of these reports confirm that other potentially useful information can be detected during these sonographic examinations. In particular, findings consistent with long-standing medical renal disease were observed in 30.5% of patients in the study in this issue2 and in 65% of patients in the study by Ritchie et al.3 Other renal findings