WEDNESDAY, May 7 (HealthDay News) -- Bipolar disorder may be overdiagnosed, say researchers at Rhode Island Hospital and Brown University.

They found that fewer than half of patients previously diagnosed with bipolar disorder were assessed using a comprehensive psychiatric diagnostic interview -- the Structured Clinical Interview for DSM-IV (SCID).

Recent reports suggest that under-diagnosis of bipolar disorder may be an issue, while this study indicates that there's an equal or greater problem with overdiagnosis, the study authors said.

They looked at 700 psychiatric patients who were interviewed using the SCID and completed a self-administered questionnaire between May 2001 and March 2005. The questionnaire asked patients if they'd been previously diagnosed with bipolar or manic-depressive disorder by a health-care professional.

While 145 of the patients said they'd been previously diagnosed with bipolar disorder, only 43.4 percent were diagnosed based on the SCID. The study also found that people diagnosed based on the SCID were much more likely to have first-degree relatives with the disorder.

The study was published online in The Journal of Clinical Psychiatry and was expected to be presented Wednesday at the American Psychiatric Association annual meeting, in Washington, D.C.

Overdiagnosis of bipolar disorder may lead to unnecessary use of medications and the risk of harmful side effects, noted lead author Dr. Mark Zimmerman, director of outpatient psychiatry at Rhode Island Hospital and an associate professor of psychiatry and human behavior at Brown University.

"Clinicians are inclined to diagnose disorders that they feel more comfortable treating. We hypothesize that the increased availability of medications that have been approved for the treatment of bipolar disorder might be influencing clinicians who are unsure whether or not a patient has bipolar disorder or borderline personality disorder to err on the side of diagnosing the disorder that is medication responsive," Zimmerman said in a prepared statement.

"This bias is reinforced by the marketing message of pharmaceutical companies to physicians, which has emphasized the literature on the delayed and under-recognition of bipolar disorder, and may be sensitizing clinicians to avoid missing the diagnosis of bipolar disorder."

Zimmerman concluded: "The results of this study suggest that bipolar disorder is being overdiagnosed, and we recommend that clinicians use a standardized, validated method in diagnosing bipolar disorder."

More information

The U.S. National Institute of Mental Health has more about bipolar disorder.