Ultrasonography in the differentiation of complicated and uncomplicated acute pyelonephritis. Differentiation of uncomplicated pyelonephritis versus complicated pyelonephritis has always been problematic. No clear physical signs or symptoms are diagnostic. To study differences between the two, we retrospectively reviewed charts of patients admitted to Charity Hospital, New Orleans, with febrile urinary tract infections. Criteria for inclusion were pyuria, positive urinary culture, and signs or symptoms of pyelonephritis. All patients underwent renal ultrasonography (US) before other diagnostic tests. US identified a potential emergency (hydronephrosis or abscess) in 11 of 98 patients (11.2%). The only significant contributing factor was the presence of diabetes mellitus, which was present in five of 11 emergent conditions and eight of 73 of the remainder (P = 0.003). US is inexpensive, easily obtainable in the emergency room, and sensitive enough to screen patients with pyelonephritis for complications. However, we believe it is mandatory in diabetics, because of the high incidence of abnormalities in this population. 