Gastroenterology and Hepatologycommon
A 72-year-old man is found to have a serum creatinine of 286 micromol/L, compared with 98 micromol/L 3 months earlier. He reports six months of poor urinary stream, nocturia and hesitancy, and examination reveals a distended, non-tender bladder. His blood pressure is 148/86 mmHg, and there is no rash, arthralgia or peripheral oedema. Which investigation is the most appropriate next step?