Indirect vs. Direct Hospital Quality Indicators for Very-Low-Birth-Weight Infants

Abstract

An increasing number of insurers today rely on evidence-based selective referral strategies to be sure that care is delivered by high-quality providers. Lacking direct-quality measures based on patient outcomes, current standards for many conditions are based on indirect quality measures such as patient volume. This retrospective study was designed to show whether volume is a useful quality indicator for the care of very-low-birth-weight (VLBW) infants. The study population consisted of 94,110 VLBW infants weighing 501 to 1500 g who were born at 332 U.S. hospitals having neonatal intensive-care units in the years 1995-2000. The average hospital admitted approximately 80 VLBW infants each year, but 25% admitted fewer than 40 per year and 10% admitted fewer than 25. The hospitals, in general, provided a high level of care; most had either a level B or a level C neonatal intensive-care unit. At hospitals admitting fewer than 50 VLBW infants, considered low-volume hospitals, an additional 10 admissions correlated with an 11% reduction in mortality (95% confidence interval [CI], 5-16%; P <0.001). The annual number of admissions explained only 9% of the variation in mortality rates at the participating hospitals. Other easily available hospital features explained another 7% of variation. Because historical volume did not relate significantly to mortality rates in 1999-2000, case volume did not prospectively identify high-quality providers. In contrast, hospitals in the lowest mortality quintile in 1995-1998 had significantly lower mortality rates in 1999-2000 (odds ratio [OR], 0.64; 95% CI, 0.55-0.76). In addition, hospitals in the highest mortality quintile had significantly higher mortality in 1999-2000 (OR, 1.37; 95% CI, 1.16-1.64). Whereas the highest and lowest mortality quintiles explained 34% of between-hospital variation in mortality in 1999-2000, the corresponding figure for the highest and lowest quintiles of patient volume was only 1%. These findings bring into question the referral of VLBW infants based on indirect quality indicators such as patient volume. Direct measures based on outcomes are more useful in guiding selective referral.