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Patient outcomes are better indicator than patient volume for selecting hospitals for VLBW babies

The JAMA Network Journals

Using a direct quality indicator, such as a survival rate, may be more effective than using an indirect quality indicator, such as patient volume, when selecting hospitals for care of a very low birth weight infant, according to a study in the January 14 issue of The Journal of the American Medical Association (JAMA).

According to background information in the article, evidence-based selective referral strategies are being used by an increasing number of insurers to ensure that medical care is provided by high-quality providers and to make sure that patients with high-risk conditions are treated in hospitals with the best outcomes. In the absence of direct-quality measures based on patient outcomes, the standards currently in place for many conditions rely on indirect-quality measures such as patient volume.

Jeannette A. Rogowski, Ph.D., of RAND, Arlington, Va., and colleagues assessed the potential usefulness of indirect-quality indicators such as patient volume for very low birth weight (VLBW) infants and compared indirect-quality indicators with direct measures, such as survival rate at a hospital.

The study included 94,110 VLBW infants weighing 501 to 1500 grams (17.7 to 53 ounces) born in 332 Vermont Oxford Network hospitals with neonatal intensive care units (NICU) between January 1, 1995, and December 31, 2000.

The researchers found that in hospitals with less than 50 annual admissions of VLBW infants, an additional 10 admissions were associated with an 11 percent reduction in mortality. "The annual volume of admissions only explained 9 percent of the variation across hospitals in mortality rates, and other readily available hospital characteristics explained an additional 7 percent. Historical volume was not significantly related to mortality rates in 1999-2000, implying that volume cannot prospectively identify high-quality providers," the authors write.

In contrast, hospitals in the lowest mortality quintile between 1995 and 1998 were found to have significantly lower mortality rates in 1999-2000 and hospitals in the highest mortality quintile between 1995 and 1998 had significantly higher mortality rates in 1999-2000. "The percentage of hospital-level variation in mortality in 1999-2000 that was forecasted by the highest and lowest quintiles based on patient mortality was 34 percent compared with only 1 percent for the highest and lowest quintiles of volume," the researchers add.

"These results suggest that the current ... standard, which is based on only volume and level of care at the NICU, would tend to be an unreliable indicator of quality in our sample of hospitals (e.g., many hospitals with low-patient volume or low-level NICUs would have better patient outcomes and vice versa).

"Our results suggest that direct-quality indicators based on patient mortality are likely to outperform indirect-quality indicators such as patient volume and more lives could potentially be saved if patient referrals were based on the former rather than the latter. The difference in mortality between the best and worst hospitals was more than 5 times larger when ranking hospitals on past-mortality rates compared with ranking hospitals on past volume. Thus, moving patients out of hospitals with high past mortality and into hospitals with lower past mortality will have a larger impact than moving patients from low-volume to high-volume hospitals," they write. (JAMA. 2004;291:202-209. Available post-embargo at


Editor's Note: This study was supported by grants from the Agency for Healthcare Research and Quality. Dr. Rogowski is a member of the Vermont Oxford Network Database Advisory Committee. Co-author Dr. Horbar is chief executive and scientific officer for the Vermont Oxford Network. Co-author Mr. Carpenter is an employee of the Vermont Oxford Network.

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