The impact of membership in a health maintenance organization on hospital admission rates for acute chest pain.

OBJECTIVE: We evaluate the impact of membership in a staff-model health maintenance organization (HMO) on hospital admission rates for patients presenting to an emergency department with acute chest pain.

DATA SOURCES AND STUDY SETTING: Primary prospective data were gathered from all 3,006 patients presenting with a chief complaint of chest pain to the emergency department (ED) of a university teaching hospital from October 1987 to November 1989.

STUDY DESIGN: Prospective cohort analysis used clinical data to stratify patients into groups at high (> or = 25%), medium (8-24%), and low risk (< or = 7%) of acute myocardial infarction (AMI). Insurance status was determined as either HMO, Medicare, commercial, Medicaid, or self-pay. Triage decisions were recorded, and patient outcomes of AMI and other final diagnoses were determined for all patients.

DATA COLLECTION METHODS: Clinical data were recorded by the physicians in the ED as part of a detailed protocol. Insurance data were recorded separately by the ED staff as part of the hospital administrative database. Patient outcomes were recorded daily by research nurses for hospitalized patients; for patients who were discharged from the ED, telephone or physician follow-up was accomplished within seven days after discharge.

PRINCIPAL FINDINGS: HMO patients were more likely to be admitted to the hospital than patients in other insurance groups in both the medium- and low-risk patient categories. Within the low-risk category, after controlling for clinical differences in a multiple logistic model, HMO membership retained an independent positive association with hospital admission compared to all other insurance groups except Medicaid.

CONCLUSIONS: For patients with acute chest pain who were at medium and low risk of acute myocardial infarction, HMO membership was associated with higher rates of hospital admission. These findings suggest that organizational factors beyond financial incentives may exercise an important influence on hospitalization rates for HMO patients.