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Patients with more chronic conditions increase hospital costs

Patient severity of illness has long been associated with increased hospital costs. The number of chronic conditions a patient has, an indication of illness complexity, also predicts greater hospital costs, according to a study by Agency for Healthcare Research and Quality (AHRQ) investigators Bernard Friedman, Ph.D., H. Joanna Jiang, Ph.D., and Anne Elixhauser, Ph.D. Along with colleague Andrew Segal of Columbia University, the researchers analyzed 2001 data from a 20 percent sample of the Nationwide Inpatient Sample (NIS) to test the independent effect of the number of different chronic conditions on cost per case, after controlling for the costliness of the principal diagnosis and other factors. The NIS, part of AHRQ's Hospital Cost and Utilization Project, contains hospital discharge summaries for 80 percent of U.S. hospital stays.

The researchers reported the three most common chronic conditions found for each of the major types of principal diagnoses as they are grouped into the chapters of the ICD9-CM coding manual. Hypertension was the most common condition and appeared as one of the top three chronic comorbid conditions for all major principal diagnoses except for mental disorders. Diabetes and coronary atherosclerosis were the other most frequent comorbid conditions. About 8 percent of hospitalized patients had no chronic condition, and another 14 percent had only one chronic condition in 2001. Yet patients with two to four chronic conditions accounted for 51 percent of all adult non-maternal hospitalizations.

The severity index had a very powerful effect on cost, with a severely ill patient having an expected cost of nearly 50 percent higher than a nonseverely ill patient with the same principal diagnosis. Even after controlling for illness severity, the number of chronic conditions significantly affected hospital costs. About 63 percent of costs were associated with patients who had three or more chronic conditions, and 28 percent were associated with patients with five or more chronic conditions. After adjusting for other patient and hospital factors, the cost per case rose significantly with each additional chronic condition, reaching a plateau at five chronic conditions. The results indicate that the high annual cost associated with multiple chronic conditions operates mostly through the number of cases, which is not offset by lower cost per case.

See "Hospital inpatient costs for adults with multiple chronic conditions," by Drs. Friedman, Jiang, Elixhauser, and Segal, in the June 2006 Medical Care Research and Review 63(3), pp. 327-346. Reprints (AHRQ Publication No. 06-R070) are available from the AHRQ Publications Clearinghouse.

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