From 1998 to 2006, rates of diabetes-related preventable hospitalizations declined for all conditions except for short-term complications. The nonsignificant decrease in age-adjusted rates for short-term complications was mainly attributable to the insignificant decrease among those aged 18–44 years. Rates decreased in all older age-groups. It is not clear why there was no significant decline in this youngest age-group.
AHRQ reported that during the period of 1994–2000, hospitalization rates dropped for uncontrolled diabetes, increased for short-term complications, and showed no changes for long-term complications and lower-extremity amputations (6
). Our results differ from AHRQ's findings. The differences reflect the different denominators used to estimate the hospitalization rates. Furthermore, using diabetic denominators, Kuo et al. (11
) showed decreased rates for ketoacidosis and lower-extremity amputations from 1992 to 2001 for Medicare beneficiaries with diabetes.
Reasons for the decline in diabetes-related preventable hospitalizations are not well understood. First, reduced rates for preventable hospitalizations could reflect improvements in primary care for individuals with diabetes. Diabetes treatment may have become more aggressive after publication of the findings from a series of clinical trials (12
). The availability of new drugs and a new form of insulin increased drug selection options and may have enhanced patient adherence to therapy (15
). With combined efforts of clinicians and various health organizations, glycemic control was improved over time (16
). From 1999–2000 to 2003–2004, the percentage of individuals having A1C <7% increased from 37 to 57% and the mean A1C fell from 7.6 to 7.1% (17
). Better glucose control would lead to reduced hospitalizations for uncontrolled diabetes.
Numerous factors can affect the rate for long-term hospitalizations and lower- extremity amputations, and information on changes in those factors during our study period was lacking. However, the percentage of diabetic patients who received an annual foot examination increased 37% between 1994 and 2005 (18
), and rates for gangrene, a common precursor to amputation, declined between 1992 and 2001 (19
). These factors may have contributed to prevention of lower-extremity amputations. In addition, the incidence of end-stage renal disease declined 21% from 1997 to 2002 (20
). Both declines in the end-stage renal disease and gangrene could have contributed to the reduced rates of long-term complications.
Second, earlier detection of diabetes could have resulted in more milder cases among the diabetic population. However, a prior study showed that individuals with newly diagnosed diabetes did not become healthier or younger during the period from 1997 to 2003 (21
Finally, a previous study showed that an increase in HMO penetration was associated with a lower rate of preventable hospitalizations (22
). We examined whether the declining preventable hospitalization rates found in our study coincided with a period of rising HMO enrollments. We found the HMO enrollments decreased from 28.6% in 1998 to 24.5% in 2006 (23
). Thus, our results are not likely to be attributable to changes in HMO penetration.
Our study is subject to several limitations. First, some hospitalizations that we considered preventable were probably not preventable. Case-by-case assessment would be required to determine the exact degree of preventability of any specific hospital admission. Second, we relied on ICD-9-CM codes to identify cases and misclassifications might exist. Third, NIS data did not contain personal identifiers, and, thus, it was impossible to identify repeated hospitalizations. Fourth, the number of states participating in the NIS changed from 22 to 37 during the study period. We do not know what bias this might have introduced. Last, a few hospital discharges for lower-extremity amputations were overlapped with a diagnosis code for one of the other three conditions. However, only <1% of cases of short-term complications and uncontrolled diabetes overlapped with lower-extremity amputations, and thus the trends for these conditions should not have been affected by lower-extremity amputation trends. Of cases of long-term complications, 16% also listed lower-extremity amputations in 2006. We reanalyzed the trends for long-term complication by excluding overlapped cases, and the conclusions remained the same.
Our study suggests that the rates for diabetes-related preventable hospitalizations have declined. It is plausible that the declining trends reflect improvement in quality of primary care for diabetes. However, further study is needed to determine the exact reasons for these declines. Hospitalization rates declined over a time when the overall burden of diabetes substantially increased. The number of individuals with diabetes is expected to increase dramatically in the future (24
). Although improvements in diabetes care that result in better outcomes are welcomed, the continuing influx of new cases of diabetes and the increasing number of existing cases remain major concerns that need to be addressed.