One mid-Atlantic health carrier is breaking off a 6-year-old affiliation with another mid-Atlantic carrier.

CareFirst Inc., Owings Mills, Md. says it is ending what it is calling a “productive and mutually beneficial” relationship with Blue Cross and Blue Shield of Delaware, Wilmington, Del., rather than continuing efforts to persuade Delaware Insurance Commissioner Matthew Denn to let it form a “contractual affiliation” with Delaware Blue.

“While both organizations would have preferred to continue their relationship, the CareFirst and [Delaware Blue] boards agreed that further appeals of the matter would be costly, disruptive to operations and not in the best interests of their respective members,” CareFirst says in a statement.

CareFirst now has about 3 million members in Maryland, northern Virginia and the District of Columbia.

Delaware Blue has about 380,000 members in Delaware.

The split should have no effect on the companies’ members and accounts, CareFirst says.

The companies have teamed up through a relatively loose “structural affiliation” since 2000.

The companies have submitted and withdrawn several applications to change the nature of their affiliation since 2000, Delaware officials say.

Denn decided in August to block the companies’ latest effort to form a contractual affiliation.

The companies also had told him of talks about seeking “yet another type of affiliation, perhaps with a different company altogether” in the near future, Denn wrote in the August decision.

Denn told CareFirst and Delaware Blue that they needed to give him many documents relating to their relationship, and that they would have to explain why they wanted specific records kept confidential if they wanted him to keep those records out of the public record.

CareFirst and Delaware Blue declined to give Denn the records on those terms, arguing that his rules would make protecting the confidentiality of sensitive records too difficult and too expensive.

Although Denn denied CareFirst and Delaware Blue’s application to form a closer relationship, “my decision in this matter is not, and in fact cannot be, based on the underlying merits of the parties’ application,” Denn writes in the August decision. “The parties have made it impossible for me to render such a decision in responsible way.”

Denn says in the August decision that the parties can resubmit their application if they use his process for deciding which records will be kept confidential.

“The primary reason [the companies] would not provide those documents is because I refused to keep them secret,” Denn says in a statement. “I continue to believe that my decision, based on the principle of open and transparent government decisions, was the right one.”