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. 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.
To assess the potential usefulness of volume as a quality indicator
for very low-birth-weight (VLBW) infants and compare volume with other potential
indicators based on readily available hospital characteristics and patient
Design, Setting, and Participants
A retrospective study of 94 110 VLBW infants weighing 501 to 1500
g born in 332 Vermont Oxford Network hospitals with neonatal intensive care
units between January 1, 1995, and December 31, 2000.
Main Outcome Measures
Mortality among VLBW infants prior to discharge home; detailed case-mix
adjustment was performed by using patient characteristics available immediately
In hospitals with less than 50 annual admissions of VLBW infants, an
additional 10 admissions were associated with an 11% reduction in mortality
(95% confidence interval [CI], 5%-16%; P<.001).
The annual volume of admissions only explained 9% of the variation across
hospitals in mortality rates, and other readily available hospital characteristics
explained an additional 7%. Historical volume was not significantly related
to mortality rates in 1999-2000, implying that volume cannot prospectively
identify high-quality providers. In contrast, hospitals in the lowest mortality
quintile between 1995 and 1998 were found to have significantly lower mortality
rates in 1999-2000 (odds ratio [OR], 0.64; 95% CI, 0.55-0.76; P<.001) and hospitals in the highest mortality quintile between
1995 and 1998 had significantly higher mortality rates in 1999-2000 (OR, 1.37;
95% CI, 1.16-1.64; P<.001). 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% compared
with only 1% for the highest and lowest quintiles of volume.
Referral of VLBW infants based on indirect-quality indicators such as
patient volume may be minimally effective. Direct measures based on patient
outcomes are more useful quality indicators for the purposes of selective
referral, as they are better predictors of future mortality rates among providers
and could save more lives.