You will have blood tests (about 2 tablespoons each time) before your dose and may have blood tests (about 2 tablespoons) 4, 8, 12 and 24 hours after your dose. Based on your test results, your study doctor may have more instructions for you, and you may need to meet with a kidney doctor while you are in the hospital. You will be hospitalized after your first dose of venetoclax to check for or treat TLS. You may need to receive fluids by vein.