in most cases, utis can be diagnosed just from the symptoms and there is no need for laboratory testing. urinalysis (testing the urine) can be used to confirm the diagnosis in complicated cases. the urine is tested for urinary nitrites, white blood cells (leukocytes), or leukocyte esterase. another test, urine microscopy, looks for red blood cells, white blood cells, or bacteria. urine culture is considered positive if it shows a bacterial colony count of greater than or equal to 103 colony-forming units per ml of a typical bacteria that causes infections of the urinary tract. cultures can also be used to test which antibiotic will work. however, women with negative cultures can still improve with antibiotic treatment. uti symptoms in old people can be vague, and diagnosis can be difficult as there is no really reliable test.