HARTFORD, Conn. — Connecticut’s highest court ruled Thursday on an issue that most people may think is already settled, saying doctors have a duty to keep patients’ medical records confidential and can be sued if they don’t.

The Supreme Court’s 6-0 decision overturned the ruling of a lower court judge who said Connecticut had yet to recognize doctor-patient confidentiality.

The high court’s ruling reinstated a lawsuit by former New Canaan resident Emily Byrne against the Avery Center for Obstetrics & Gynecology in Westport.

“It’s particularly important for not only my client but for all patients receiving medical care in Connecticut,” Byrne’s lawyer, Bruce Elstein, said. “This case has established for the first time that there’s a duty of confidentiality. … That’s groundbreaking.”

Byrne, who now lives in Montpelier, Vermont, alleges the doctor’s office, without her permission and without warning, sent her medical file to a probate court in New Haven in 2005 under a subpoena issued by an attorney for her child’s father. She alleges the father was then able to look at her medical file and use the highly personal information to harass, threaten and humiliate her, including filing seven lawsuits and threatening to file criminal complaints.

The father had subpoenaed the medical file in a paternity case.

Byrne sued the Avery Center in 2007 for alleged negligence in failing to protect her medical file, infliction of emotional distress and failing to follow state and federal medical privacy laws. But state Judge Richard Arnold in Bridgeport dismissed her claims in 2015.

Arnold ruled that Connecticut law, unlike laws in many other states, had yet to recognize a duty of confidentiality between doctors and their patients, or that communications between patients and health care providers are privileged under common law. Byrne appealed Arnold’s decision.

The attorney for the Avery Center, James Biondo, did not return a message seeking comment Thursday.

Biondo had argued there is no common law duty for Connecticut doctors to keep patients’ information confidential. He also wrote in court documents that Byrne signed a statement for the Avery Center confirming she had reviewed the center’s privacy policy, which notifies patients that it is under no obligation to seek their authorization when complying with subpoenas.

There is a state law that prohibits disclosure of patient information by doctors, but there is an exception that allows for information to be released without the patient’s consent “pursuant to … the rules of court.”

Byrne accused the Avery Center of failing to comply with the state law as well as the federal law on patient information confidentiality — the Health Insurance Portability and Accountability Act, or HIPAA. The federal law says a medical provider can disclose patient information in response to a subpoena not issued by a judge, if reasonable efforts have been made to notify the patient of the subpoena.

Byrne said she was not given an opportunity to object to the Avery Center releasing her medical file under subpoena.

The Avery Center said the appeal centered on common law and HIPAA was irrelevant.

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This story corrects the summary to say the father of Byrne’s child was able to view Byrnes’ medical file, not the husband of her child.