Associations between outpatient and inpatient service use among persons with HIV infection: A positive or negative relationship?

Objective. To examine the prospective association between frequency of outpatient visits and subsequent inpatient admissions. Data Sources. Medical record data on 13,942 patients with HIV infection seen in 10 HIV speciality care sites across the United States. Study Design. This observational study followed a cohort of HIV-infected patients who were in care in the first half of 2001. Numbers of inpatient admissions and outpatient visits were calculated for each patient for each 3-month period, from 2001 through 2004. Analysis. Negative binomial and logistic regression analyses using random-effects models examined the effects of inpatient admissions and outpatient visits in the previous period on inpatient and outpatient service utilization, controlling for background characteristics and HIV disease stage. Results. For 3-month periods, between 5 and 9 percent of patients had an inpatient admission. The linear association between number of outpatient visits and any inpatient admission in the subsequent period was positive (adjusted odds ratio=1.05; 95 percent confidence interval [CI]=1.04, 1.06). However, patients with zero prior outpatient visits had significantly greater admission rates than those with one prior visit. Hospitalization rates were also higher among those with a prior hospitalization and those with more advanced HIV disease. Conclusions. These results suggest a J-shaped relationship between outpatient use and inpatient use among persons with HIV disease. Those in worse health have greater utilization of both inpatient and outpatient care. However, having no outpatient visits may also increase the likelihood of subsequent hospitalization. Although outpatient care cannot be justified as a cost-saving mechanism, maintaining regular clinical monitoring of patients is important.