Ambulatory care fragmentation and hospitalization among veterans with diabetes.

To determine whether having a usual provider of care (UPC) outside the Veterans Health Administration (VHA) and whether having highly fragmented care (regardless of the providers' health system affiliations) increased the risk of hospitalization among veterans with diabetes. Retrospective dynamic cohort analysis of all veterans with diabetes 65 years and older enrolled nationally in both VHA and Medicare from 2005 to 2010, using VHA-Medicare linked data. We used 5 two-year study periods, assessing ambulatory care in the first year of each 2-year period and any hospitalization in the second year. We used longitudinal generalized estimating equation models to test the associations of the affiliation (VHA vs non-VHA) of the UPC and the extent of fragmentation with hospitalization, adjusting for potential confounders. Highly fragmented care was defined as a reversed Bice-Boxerman Index of at least 0.85, which was equivalent to the 75th percentile. Having a UPC outside the VHA was associated with 11% increased odds of hospitalization (95% CI, 10%-12%). Having highly fragmented care was associated with 7% increased odds of hospitalization (95% CI, 6%-8%). Having both a UPC outside the VHA and highly fragmented care was associated with 19% increased odds of hospitalization (95% CI, 18%-20%). Among veterans with diabetes enrolled in both VHA and Medicare, having both a UPC outside the VHA and highly fragmented care was associated with higher odds of hospitalization than either of these ambulatory patterns alone.