Weekend Versus Weekday Mortality for Thrombotic Thrombocytopenic Purpura (TTP) Related Hospitalizations in the United States: Data from the National Inpatient Sample
Authors: Giri Smith , Pathak Ranjan , Aryal Madan Raj , Karmacharya Paras , Martin Michael G 
Published: October 2019

Abstract
Introduction: Previous research has shown that weekend hospital admissions are associated with an increased mortality in comparison to weekday admissions for a number of emergent conditions including myocardial infarction [Relative Risk (RR) 1.048; 95% confidence interval [CI], 1.022 to 1.076; P value <0.001], pulmonary embolism (RR 1.17, 95% CI 1.03 to 1.34, P value <0.01) and gastrointestinal hemorrhage (RR 1.17, 95% CI 1.03 to 1.34, P value <0.01) . Thrombotic Thrombocytopenic Purpura (TTP) is a hematological emergency with a significant morbidity and mortality if not recognized early. However, studies evaluating if a similar "weekend" effect exists in TTP are lacking.
Methods: We used the Nationwide Inpatient Sample database to identify patients admitted with TTP in the United States using ICD 9 CM code 446.6 from 2009 to 2011. Baseline data for demographic variables, age, gender, race, hospital characteristics- region, hospital type (rural versus urban, teaching versus non-teaching), bed-size, insurance payer and comorbidities were derived for weekend and weekday admissions. Logistic regression analysis was used to calculate the adjusted relative risk of in-hospital mortality of weekend versus weekday admissions. Data analysis was done using STATA 13.0 (College Station, TX: StataCorp LP)
Results: Of the 6634, estimated TTP related hospitalizations, 19.5 % were admitted on the weekends and 80.5 % admitted on the weekdays. The mean age was 48±0.5 years and 66.4 % were females. A higher in-hospital mortality rate was seen among weekend admissions as compared to weekday admissions (RR 1.32, 95% CI 1.30-1.33, p value <0.01). On multivariate analysis (table 1), weekend admission remained as an independent predictor of increased mortality (adjusted RR 1.16, 95% CI 1.15-1.17, P value <0.01) after adjusting for other confounders including age, gender, comorbidities, hospital type and size. Similarly, acute kidney injury (adjusted RR 3.41, 95% CI 3.34-3.43, P value <0.001), stroke (adjusted RR 5.46, 95% CI 5.31-5.62, P value <0.001), and sepsis (adjusted RR 6.57, 95% CI 6.40-6.75, Pvalue <0.001) were associated with significantly increased risk of mortality among patients with TTP (table 1).
Conclusions: A significantly higher in-hospital mortality occurs among TTP patients admitted on the weekends as compared to weekdays. Future research should focus on identifying the underlying factors for this difference so that quality improvement measures could be taken to mitigate this difference.
Table 1: Logistic Regression Analysis showing the adjusted relative risk (RR) of various patient and hospital characteristics in predicting in-hospital mortality for patients with TTP. Variable Adjusted RR 95% CI of Adjusted RR P value Weekend admission 1.16 1.15-1.17 <0.001 Pay - Medicare - Medicaid - Private including HMO - self-pay - no charge - other 1.0 1.33 1.19 1.63 1.36 2.02 .. 1.28-1.38 1.14-1.25 1.50-1.77 1.11-1.67 1.73-2.36 <0.001 <0.001 <0.001 <0.001 <0.001 Race - white - black - hispanic - asian or pacific islander - native american - other 1.0 1.01 0.93 1.13 1.05 1.07 0.98-1.03 0.89-0.97 1.07-1.19 0.94-1.16 1.02-1.13 0.47 0.003 <0.001 0.34 0.003 Region - Northeast -Midwest - South - West 1 0.92 1.05 0.97 0.86-0.98 0.99-1.11 0.91-1.04 0.01 0.06 0.48 Co-morbidities - smoking - obesity - dyslipidemia - hypertension - diabetes mellitus - peripheral vascular disease - coronary artery disease - acute kidney injury - chronic kidney disease - stroke - sepsis 0.90 0.78 0.60 0.68 0.99 1.32 1.06 3.41 1.10 5.46 6.57 0.88-0.92 0.76-0.79 0.59-0.61 0.67-0.69 0.97-1.00 1.29-1.34 1.05-1.07 3.34-3.43 1.08-1.11 5.31-5.62 6.40-6.75 <0.001 <0.001 <0.001 <0.001 0.12 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Age 1.04 1.043-1.046 <0.001 Female 0.78 0.78-0.79 <0.001 Hospital Type - rural - urban non teaching - urban teaching 1.0 0.92 1.05 0.88-0.97 0.99-1.11 0.002 0.061 Bed size - small - medium - large 0.95 1.01 0.89-1.01 0.96-1.07 0.11 0.51

Disclosures
No relevant conflicts of interest to declare.