Question: We're in disagreement about which CPT® code to use for BCG bladder instillation due to the descriptor wording for 51720. Our patients leave the facility immediately after the instillation. Should we use 51700 when the patient does not remain or void post-instillation in the facility? North Dakota Subscriber Answer: There can sometimes be confusion about the correct use of 51720 (Bladder instillation of anticarcinogenic agent [including retention time]) in the situation you describe because of the phrase "including retention time." Even if the patient voids at home, however, reporting 51720 is still correct. Submitting 51700 (Bladder irrigation, simple, lavage and/or instillation) instead is not an accurate assessment of what occurred.