The diagnosis of a patient with mental health problems may be the only obvious, easy-to-identify factor that correlates with the cost of the patient’s care.

Addiction researchers at Harvard University come to that conclusion in a study backed by ValueOptions Inc., Reston, Va.

ValueOptions manages treatment of addiction, depression and other mental health problems.

The Harvard researchers used millions of claims filed from January 2002 to December 2004 by members of 4 regional health plans in the Mid-Atlantic and Northeast.

The researchers considered member characteristics such as age, gender and diagnosis along with factors such as deductibles and other elements of benefit plan design; the number of mental health care providers in a member’s ZIP code; and whether the member was in a health maintenance organization plan, preferred provider organization plan or point-of-service plan.

“Contrary to expectations, a member’s diagnosis was the only variable that predicted service costs and units,” ValueOptions reports. “The member’s age and gender, the number of available providers, the benefit design, and the product line did not add to estimation of service costs or utilization.”

About 8.6% of plan members studied filed at least 1 claim for outpatient services, and about 0.8% filed a claim for inpatient services, ValueOptions says.

Diagnoses for depression, adjustment disorders and anxiety disorders accounted for about 75% of outpatient claims.

For inpatient claims, depression, bipolar disorder, alcoholism and adjustment disorders were the most frequent diagnoses, ValueOptions says.