Discussion
Currently there are no guidelines as to what constitutes a 'safe' day of discharge blood pressure range. In our study, a SBP of 120-160 mmHg is associated with the lowest risk of adverse events in the initial 30-days after a hospitalization.  The odds of adverse outcomes steeply increased below SBP's of 100 mmHg and above 160 mmHg.  Prior studies report increased risk of adverse outcomes when the systolic blood pressure is less than 90 -100 mmHg — we note a significantly increased in risk in when the SBP was below 120 mmHg.
Our study merely observes an association. We do not claim that there is a causal relationship between abnormal SBP at discharge and adverse events. It is likely that patient cohorts with markedly abnormal SBP are qualitatively different than the cohort of normotensive patients.  Although we have tried to adjust for a number of the most relevant variables, many unmeasured variables could be potential confounders. In the future, causal approaches such as propensity matching may shed light on the nature of the observed association. 
Our findings may not be applicable for subgroups such as patients with heart failure, end stage liver disease, or post-acute stroke populations.  There may have been variations in the method of inpatient blood pressure measurements.  Furthermore, blood pressure measurements may be falsely elevated due to factors such as withdrawal, anxiety, pain, and urinary retention.   Finally, we do not have information on readmissions outside our large hospital network, thus our rate of readmissions may be underestimated.
Despite these limitations, our study documents an interesting observation and reminds clinicians to be cognizant of abnormal discharge systolic blood pressure and its association with increased 30-day mortality and readmission.  Further randomized controlled trials are needed to elucidate the relationship between discharge systolic blood pressure and post discharge outcomes.  
References:
1. Avraham Weiss, Yaron Rudman, Yichayaou Beloosesky, Amit Akirov, Tzippy Shochat & Alon Grossman (2017) High blood pressure variability predicts 30-day mortality but not 1-year mortality in hospitalized elderly patients, Blood Pressure, 26:5, 259-263
2. Nguyen, Oanh Kieu, et al. "Vital signs are still vital: instability on Discharge and the risk of Post-Discharge adverse outcomes." Journal of general internal medicine 32.1 (2017): 42-48.
3. Williams, Bryan, et al. "2018 ESC/ESH Guidelines for the management of arterial hypertension." European heart journal39.33 (2018): 3021-3104.
4. Axon, R. Neal, Mason Turner, and Ryan Buckley. "An update on inpatient hypertension management." Current cardiology reports 17.11 (2015): 94.
5. Axon, R. Neal, Laura Cousineau, and Brent M. Egan. "Prevalence and management of hypertension in the inpatient setting: a systematic review." Journal of hospital medicine 6.7 (2011): 417-422.
6. James, Paul A., et al. "2014 evidence-based guideline for the management of high blood pressure in adults: report from the panel members appointed to the Eighth Joint National Committee (JNC 8)." Jama 311.5 (2014): 507-520.