Recent Trends in the Incidence and Outcomes of Thrombotic Thrombocytopenic Purpura in the United States: Data from the 2009-2014 National Inpatient Sample

Background

Thrombotic Thrombocytopenic Purpura (TTP) is a hematological emergency that can be fatal if not promptly recognized and treated. Given its rarity, there is paucity of data regarding the disease burden and outcomes. We used a large administrative database to examine recent incidence and outcomes of TTP in the United States.

Methods

We used the 2009-2014 National Inpatient Sample database, which is the largest publicly available all-payer inpatient database in the US, to identify patients ≥18 years with primary and secondary diagnoses of TTP (International Classification of Diseases, 9^th Revision, Clinical-Modifications [ICD-9-CM] code 277.88) who underwent plasmapheresis (ICD-9-CM procedure code 99.71). We only included patients who received therapeutic plasmapheresis (ICD-9-CM procedure code 99.71) during hospitalization to capture active cases of TTP and improve coding accuracy. We calculated annual incidence of TTP specific hospitalizations by dividing the total number of TTP related hospitalizations in each year by the corresponding total all-cause hospitalizations recorded in the database in the same year. Annual incidence, mortality, length of stay (LOS), costs were calculated for each year 2009-2014, fitted into a log-linear model and compared using Monte Carlo permutation test to study the changes in trend. Statistical analyses were done using STATA version 13.0 and Joinpoint Regression Program version 4.5.0.1.

Results

A total of 32,609 cases of TTP were identified among 219,490,468 hospitalizations during the study period. Average annual incidence of TTP was 14.89 per 100,000 hospitalizations with an annual percent change (APC) of 0.99 which was statistically not significant (95% CI -3.2 to 5.4, p=0.6) (Figure 1). There was no significant change in the rate of plasmapheresis use from 2009 (40.11%) to 2014 (37.68%) (Figure 2). Similarly, there was no significant annual change in the in-hospital mortality (mean 10.2%), LOS (mean 13.1 days) and total hospital charge (mean $160,574; cost adjusted for yearly inflation using Consumer Price Index, Bureau of Labor Statistics) (Table 1).

Discussion

Our study shows that the annual incidence of TTP has remained unchanged (14.89 per 100,000 adult hospitalizations) in the recent years. Similarly, the outcomes in terms of in-hospital mortality, LOS and total cost of hospitalization have not improved.

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