A nurse is caring for a 68-year-old male client in the clinic who reports difficulty urinating over the past 2 days. He states he feels the urge to void but is only able to pass small amounts of urine. He also reports lower abdominal discomfort and a sensation of bladder fullness. On assessment, the nurse notes a firm, distended bladder upon palpation. Which of the following diagnostic tests should the nurse anticipate the provider will order to confirm urinary retention?