Question: My ob-gyn admits patients for observation, but the patients occasionally stay for only four to six hours on the same day. I don't feel comfortable charging same-day observation admit and discharge for stays that short. How should I bill for these short observation stays? Massachusetts Subscriber Answer: Although CPT does not outline any time constraints for using the same-day observation admission and discharge codes (99234-99236), Medicare states that a patient must be in observation for more than eight hours to report these codes. If the patient is admitted as observation status for less than eight hours, you should use the observation admission codes (99218-99220) only. Some Medicaid programs have developed their own definition, and you should determine which, if any, your state program applies. Generally, however, if the patient is in observation for less than an hour, you should report these services with an outpatient E/M code (99201-99215).