Burden of Illness Among Medicare and Non-Medicare Populations with Acquired Thrombotic Thrombocytopenic Purpura, 2010-2018

Background and Objective

Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare hematologic disorder that causes microvascular thromboses and can lead to serious and life-threatening medical complications. The aim of this study was to describe aTTP-related resource utilization, cost, complications, and overall survival (OS) among US Medicare and non-Medicare populations following aTTP episodes.

Methods

This retrospective study utilized administrative claims data for Medicare Fee-for-Service (FFS) beneficiaries (100% sample) and a sample of commercial, managed Medicaid [MM], Medicare Advantage [MA] plan members from the Inovalon MORE² Registry. Patients aged 18+ with aTTP were identified using a validated algorithm (Wahl et al, 2010): ≥1 hospitalization for thrombotic microangiopathy + therapeutic plasma exchange (TPE) between 2010 and 2018. Patients with hemolytic-uremic syndrome or other conditions mimicking aTTP during same hospitalization were excluded. Outcomes included characterization of index hospitalization (including length of stay), diagnosis-related group (DRG) payment amount (2019 US$ [Medicare payments also included outlier payments]), and risk of mortality. OS was compared for Medicare FFS patients with aTTP to a 1:1 matched cohort of Medicare FFS beneficiaries without aTTP (matched on age, gender, region, index year, socioeconomic status, disability insurance benefits, and Charlson comorbidity index score). Median survival time and 1-year/2-year survival rates were estimated using Kaplan Meier methodology and hazard ratio was obtained using Cox proportional hazard model. In a subgroup analysis of aTTP patients across payer channels with at least 6 months of baseline and 1 month of follow-up data, percentage of patients with readmission for TPE (exacerbation if <30 days post-discharge; relapse if >30 days post-discharge) and rate of post-discharge clinical complications per 100 person-years was calculated.

Results

During the 9-year period, 2,279 patients met the study criteria for aTTP; 65.2% (N=1,486) were enrolled in Medicare FFS: 13.6% (N=312) in commercial, 15.7% (N=358) in MM, and 5.4% (N=123) in MA. Mean (SD) age (in years) varied by payers as expected: Medicare FFS: 65.9 (13.9); MA: 63.8 (13.6); commercial: 45.0 (14.3); MM: 37.5 (14.0). Mean (SD) hospitalization for index event ranged from 12.4 (9.4) to 15.8 (11.8) days; majority of patients required intensive care (Medicare FFS: 61.4% [mean (SD) ICU days: 8.3 (8.2)]; MA: 61.8%; commercial: 62.2%; MM: 60.1%). Among Medicare FFS patients, 15.7% died during initial hospitalization and 21.0% died within first 30 days of the event (mean (SD) time to death: 11.7 (7.2) days). Among matched cohorts of Medicare patients with and without aTTP (N=833 in each cohort), OS was lower for patients with aTTP (Figure 1). Specifically, 1-year survival rates among aTTP patients was 71.8% (95% CI: 68.6%–74.8%) vs. 95.6% (94.0%–96.8%) for those without aTTP. Two-year survival rates among aTTP patients was 66.6% (63.2%–69.8%) vs. 91.1% (88.8%–92.9%) for those without aTTP. Risk of mortality was 2.9 times higher for patients with aTTP vs. without aTTP (95% CI: 2.4–3.4). Mean (SD) DRG payment for index hospitalization varied by payers: Medicare FFS: $29,024 ($32,565); MA: $12,860 ($6,981); commercial: $9,996 ($5,995); MM: $10,470 ($7,370). During follow-up, 18.4%–22.4% of patients experienced aTTP-related exacerbation [Medicare FFS: 18.4%; MA: 21.9%; commercial: 22.4% and MM: 22.2%]. Annual incidence rate of relapse per 100 person-years was 5.6 [Medicare FFS: 3.6; MA: 8.7; commercial: 10.4 and MM: 14.7] and annual incidence rate of complications per 100 person-years was 16.7 [Medicare FFS: 15.5; MA: 20.5; commercial: 21.7 and MM: 19.1].

Conclusions

This is the first real-world study evaluating burden of illness among aTTP patients in the US across payer types. Despite being treated with TPE, patients with aTTP have high acute mortality and are nearly three times as likely to die compared with the general Medicare population without aTTP. During the initial hospitalization, many required intensive care. Following discharge, approximately 1 in 5 was readmitted within 30 days and had higher incidence for clinical complications associated with aTTP. The study findings highlight the need for more effective therapies to reduce disease burden for this population.