No, you are not required to acquire patient authorization or consent to send MD reports, at least in the United States. The Health Insurance Portability and Accountability Act (HIPAA) Privacy Rule states that a health care provider is permitted to use or disclose protected health information (PHI) for treatment, payment, and operational (TPO) purposes without the individual's authorization or consent. Sending MD reports to a patient's provider falls under treatment purposes. See the definition of "treatment" at 45 CFR 164.501. 

According to the HIPAA Privacy Rule, patient authorization is only required for PHI uses and disclosures that fall outside of TPO purposes. Patient consent is optional and is used to obtain a patient's permission to use or disclose PHI for TPO purposes. Covered entities are free to establish their own procedures regarding patient consent.

Please reference your organization's policies and procedures as they may be more stringent than HIPAA.