Seniors account for one of every three dollars spent on health care in the U.S., with the total spent on geriatric care reaching $368.1 billion in 2008. Of this amount, the majority is spent treating just five medical conditions, says the Agency for Healthcare Research and Quality (AHRQ) in a new report. In 2008, 86 percent of the nation’s seniors were treated for at least one of these conditions, with Medicare picking up the lion’s share of the tab.

These maladies that occur with such frequency in the senior population are: cardiopathy, cancer, osteoarthritis and other joint diseases, hypertension and disorders resulting from trauma.

Cardiopathy, or heart disease, was treated in 12.7 million adults over age 65 and accounted for $48.4 billion in health-care costs in 2008, making it overall the most expensive disease of the five. The average bill was $3,820 per patient.

The treatment of cancer racked up $32.2 billion, averaging $4,028 per person; osteoarthritis and joint disease accounted for $24.8 billion, or about $1,856 per person; hypertension averaged $1,002 per person for a total of $23.8 billion; and the treatment of disorders resulting from trauma averaged $3,742 per person, or $20.5 billion in total.

For more on senior health care, see:

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Senior health update: Intervention prevents hospital readmissions

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