Discussion

In this study we aimed to compare the utility of vital sign instability to the established HOSPITAL score and LACE index predictors for all cause hospital readmission within 30 days of discharge in our study population. This study indicates that vital sign instability is not a significant predictor of hospital readmission in a moderate sized not-for-profit university-affiliated tertiary care hospital in the Midwestern United States.
Significant differences in the prevalence of vital sign instability (13% vs. 20%) and patient demographics exist between this study and the results of Nguyen and colleagues (Nguyen et al., 2017).  Patients in this study were more likely to be male (53% vs 46%), had more emergency department visits (1.15 vs. 0.28) and hospital admissions (0.94 vs. 0.31) in the past year, and had a longer hospital length of stay (8 vs. 4). It is not clear if these differences reflect fundamental differences, such as severity of illness or access to outpatient medical care, between the studied populations or variations between local practice patterns regarding the clinical decision of when to discharge a patient from the hospital. 
The performance of the HOSPITAL score and LACE index in this study was comparable to prior investigations at this center (Robinson 2016, Robinson and Hudali, 2017) and validation studies of the HOSPITAL score (DonzĂ© et al, 2016, Garrison et al., 2016) and LACE index (van Walraven et al., 2010, Garrison et al., 2016). 
This single center retrospective study indicates that the HOSPITAL score and LACE index are superior to vital sign instability at predicting all cause hospital readmissions within 30 days for a medical hospitalist service at a university-affiliated hospital. The study population contains patients who were admitted more than one time within the study period. Inclusion of these patients is essential for this analysis because it reflects the criteria used by the Medicare HRRP to assess readmission rates (Centers for Medicare and Medicaid Services, 2016). The endpoint of all cause readmissions is highly relevant because it is a significant marker of hospital quality under the Medicare program for hospital reimbursement through the HRRP.  Under this program, hospitals with high readmission rates can face financial penalties. 
Unfortunately, vital sign instability alone is not a sufficiently powerful readmission risk predictor to have utility in this setting. Reliance on more complex, but effective risk prediction tools such as the LACE index and HOSPITAL score is essential for identifying patients at increased risk of hospital readmission. Hospital readmissions are complex and multifactorial, underscored by the evidence presented in a recent meta-analysis that no single intervention was shown to be adequate alone in preventing readmission (Leppin et al., 2014).
This study shows that vital sign instability alone is not useful in a moderate sized community based hospital to identify patients at high risk of readmission. However, there several important limitations; this study is retrospective, single center, focused on medical patients, small sample size, and shaped by local practice patterns (no oncology admitting service, longer length of hospital stay, more frequent emergency department visits, and other factors). These limitations may reduce the generalizability of these results. 
 

Conclusions

 The presence of vital sign instability at the time of discharge did not appear to be a useful tool in moderate sized community hospitals to identify patients at high risk of hospital readmission within 30 days. The established risk assessment tools of the HOSPTIAL score and LACE index had superior performance in the study population. 
Further research is needed to identify readmission risk assessment tools that are easy to implement at the point of care that are effective over a wide range of patient populations and medical practice patterns.