The relationship between patient volume and quality of outpatient care for diabetic patients in Taiwan

Background and objectives. The evidence for a "higher volume and better outcomes" relationship is substantial and compelling for certain rare and risky procedures; however, such volume-outcome associations have rarely been studied for chronic diseases such as diabetes. The objective of this study is to assess the extent to which diabetic patients receive biannual hemoglobin A1C (A1C) measurements and to examine the relationship between provider volume of diabetic patients and quality of ambulatory diabetic care in Taiwan. Methods. This was a retrospective observational study using nationally representative data from the Taiwan National Health Insurance program between January 1998 and December 1999. The relationship between annual clinic and physician volumes of diabetes and patients' likelihoods of receiving biannual A1C measurements were examined before and after comprehensive case-mix adjustments. Results. The quality of ambulatory diabetic care was far from optimal, and significant variations were noted among patient income levels, treatment modalities, frequency of visits, and continuity of care. There were also substantial quality variations among physician specialties, as well as by hospital ownership and types. However, this study found that clinic and physician patient volumes were associated with the quality of ambulatory diabetic care. Before comprehensive case-mix adjustments, diabetic patients cared for at higher-volume clinics or by higher-volume physicians were more likely to receive biannual A1C measurements than those who were cared for at lower-volume clinics or by lower-volume physicians. This relationship was not linear. Upper volume thresholds were identified, and the probability of receiving biannual A1C did not go up as clinic or physician volume increased. After full risk adjustment, however, physician volume seemed to be more important than clinic volume. Above a certain patient caseload, the quality of ambulatory diabetic care decreased as the clinic volume increased. This volume effect was particularly significant for high-volume physicians and large hospitals. Conclusions. The study findings have significant implications for healthcare policies, especially as cost containment becomes increasingly important in Taiwan. Nationwide quality assessment and improvement using process-based indicators is recommended for policy makers and providers to counteract the potential threats to quality of care by the volume-driven payment system.