Please try again. Urinary tract infections (UTIs) are caused by bacteria that invade the urinary system and multiply to cause an infection. Urinary tract infections involve either the upper (kidneys) or lower (ureters, bladder, urethra) urinary tract. A urinary tract infection is suspected with the presence of increased bacteria and white blood cells in the urine. The additional presence of casts is usually indicative of an upper urinary tract. Most urinary casts contain Tamm Horsfall protein, a mucoprotein secreted by the renal tubular cells of the distal and collecting tubules in the kidney. Lower urinary tract infections are characterized by pain or burning with urination (dysuria), lower abdominal pain, and minimal protein in the urine.