Diabetes was not found to be associated with increased odds of death in people aged over 65 years with an unadjusted odds ratio of 0.89 (p < 0.001). Diabetes diagnosis has an interaction with age. Accumulating age reduces its impact to the point that a diagnosis of diabetes may predict a better outcome in the very elderly (aged more than 80 years, see Fig. 1a. This may be due to immortal time bias (only the healthiest diabetics survive to ages beyond 80 years) [18, 19]. At the very least, it confirms that diabetes in the very elderly does not convey a worse prognosis.
Most of studies that deal with mortality and diabetes are longitudinal studies [20–24]. There only a few studies that explore in-hospital mortality associated with diabetes and these are disease specific [25–27]. Two of the studies show not effect on inpatient mortality [25, 27]. The third showed an odds ratio of 1.31 (1.04–1.65) for mortality in diabetics with foot disease . It is possible that there are disease specific subsets that are at higher risk, but this was not the aim of the present study.
Similar to mortality, diabetes diagnosis had less impact with increasing age with shorter lengths of stay in the very elderly (see Fig. 1b) despite diabetics having overall longer LOS. This is consistent with other studies [25, 27–29]. The present study differs from other works by including only people over 65 years and adjusting for the confounding of disease burden by using the CCI. It remains consistent with the larger body of clinical studies. Furthermore, also consistent with these studies is the magnitude of the effect, which is small.
Hospital acquired adverse events were higher in the diabetic cohort. It was not modified when adjusting for age. This study used a validated but not extensively used method of detection of hospital acquired diagnosis [17, 30–34]. Using this method, Cromarty et al were able to show that 29.3% of diabetics developed hospital acquired events compared to 13% of non-diabetics . The present study found a much higher proportion of HADX overall, probably related to this studies older cohort.
This study demonstrated that the odds of being re-admitted within 28 days of discharge was associated with the diagnosis of diabetes and these odds were not influenced with increasing age. Caughey et al identified older people with co-morbidities as those most likely to be re-admitted within 30 days . The present study adjusted for the presence of comorbidity and found little difference, providing some support for their result. Dungan identified those with poor glycaemic control as those most likely to be re-admitted. Clinical measures were not undertaken in the present work.
The present study did not show why the diagnosis of diabetes did not have an impact on mortality in the very elderly. However it did confirm the anecdotal experiences of experienced geriatricians. Recently, the management of diabetes in the older person has changed with less rigid control goals . There is evidence that rigid control may not have the benefits seen in younger people. A converse viewpoint is that diabetes may not be as harmful in older people and so its control does not need to be as tight.
The current study has limitations. It is a retrospective audit of hospital administrative data. Hospital databases have not been designed for clinical investigations. However, the large amounts of data can be used for association. Several validation studies have been conducted with sensitivities and specificities of up to 95.6% and 98.5% respectively . However, studies also warn about changes in coding rules that occur over time, such as the changes that occurred in the definitions of diabetes in 2011 . This has resulted in a decrease level of reporting. This study commenced in 2012 for that reason.
This study did not use specific clinical measures. Medication usage, glycaemic control and measures of frailty are such measures. Several small works have examined hospital outcome based on these clinical measures [40–43]. The current study used administrative data only, it was beyond the scope of this study to do so. Certainly, prospective studies that explore the effects of glycaemic control and frailty on hospital outcomes are needed.