The role of outpatient facilities in explaining variations in risk-adjusted readmission rates between hospitals

Abstract

Objective: Validate risk-adjusted readmission rates as a measure of inpatient quality of care after accounting for outpatient facilities, using premature infants as a test case.

Study setting: Surviving infants born between January 1, 1998 and December 12, 2001 at five Northern California Kaiser Permanente neonatal intensive care units (NICU) with 1-year follow-up at 32 outpatient facilities.

Study design: Using a retrospective cohort of premature infants (N=898), Poisson's regression models determined the risk-adjusted variation in unplanned readmissions between 0-1 month, 0-3 months, 3-6 months, and 3-12 months after discharge attributable to patient factors, NICUs, and outpatient facilities.

Data collection: Prospectively collected maternal and infant hospital data were linked to inpatient, outpatient, and pharmacy databases.

Principal results: Medical and sociodemographic factors explained the largest amount of variation in risk-adjusted readmission rates. NICU facilities were significantly associated with readmission rates up to 1 year after discharge, but the outpatient facility where patients received outpatient care can explain much of this variation. Characteristics of outpatient facilities, not the NICUs, were associated with variations in readmission rates.

Conclusion: Ignoring outpatient facilities leads to an overstatement of the effect of NICUs on readmissions and ignores a significant cause of variations in readmissions.

Figure 1

The Timing of Hospital Readmission after Hospital Discharge. Peak time for readmission was within 4 months of discharge, with a consistent but low volume of readmissions out to 1 year

Figure 2

Amount of Variation in Readmission Rates Attributed to Patient-Level Factors (black bars), Site of NICU Care (gray bars), or Site of Outpatient Care (white bars) Note: Factors were added to the Poisson's model one at a time, in three sequences: (1) Patient factors and NICU factors (Model N); (1) Patient factors, NICU factors, and outpatient facility variables (Model N+O); or (2) Patient factors, outpatient facility variables, and NICU factors (Model O+N). The marginal contribution to R² from the addition of a variable is shown. Outcome measures where the NICU was statistically significant in the naïve Models N are starred; outcome measures where the outpatient facility, but not the NICU, was statistically significant in the full model are shown with a plus sign.

Figure 3

Adjusted Association between Readmission Rates and Three Measures of Outpatient Quality of Care Note: For each measure, the incidence rate ratio is the change in readmission rates by attending a poor-quality facility compared with a high-quality facility. Statistically significant associations are shown as the ^*p<.05 or ^**p<.01. Facilities with higher-than-expected use of oral albuterol or antibiotics for viral conditions had higher rates of readmissions at three of the four time periods studied.