The Use of a Large Electronic Health Records System to Define and Characterize a Thrombotic Thrombocytopenic Purpura Population

Background: Thrombotic thrombocytopenic purpura (TTP) is a rare life-threatening microangiopathy due to a deficiency of the von Willebrand factor (VWF)-cleaving protease ADAMTS13. Microangiopathic hemolytic anemia, severe thrombocytopenia and ischemic end organ injury due to microvascular thrombi are the defining features of TTP. TTP can be caused by auto-antibodies against ADAMTS13 enzyme (immune TTP [ITTP]) or by inherited mutations of the ADAMTS13 gene (congenital TTP [CTTP]). Therapeutic plasma exchange (TPE) to replenish ADAMTS13, with or without steroids, has been the mainstay of treatment. Due to the auto-immune nature of ITTP the International Society on Thrombosis and Hemostasis (ISTH) made a strong recommendation in 2020 to add corticosteroids to TPE for ITTP and a conditional recommendation to add the CD20 inhibitor rituximab as well the VWF monoclonal antibody caplacizumab.

Objective: To define and characterize TTP in a living population from a large electronic health record (EHR) database in terms of disease prevalence, demographic characteristics and therapeutic interventions and procedures in light of recent ISTH guidelines.

Methods: We conducted a study of data from TriNetX Analytics Network, which contains EHRs from >140 million individuals from 79 Health Care Organizations in the US. We used ICD-10-CM diagnosis codes, ATC and CPT codes applied in the last 10 years to evaluate TTP disease prevalence, therapeutic interventions and procedural interventions respectively. Eligibility criteria applied to define the TTP cohort were as follows:

Inclusion criteria:

• ICD-10 M31.1 diagnosis of thrombotic microangiopathy (TMA)

• History of thrombocytopenia (platelet volume ≤150,000 per microliter)

• ICD-10-PCS code for pheresis of plasma or a CPT code for therapeutic apheresis, for plasma pheresis

Exclusion criteria:

• ICD-10-CM codes linked to etiologies of TMA other than TTP (hemopoietic stem cell-associated TMA [M31.11], hemolytic uremic syndrome [D59.3], disseminated intravascular coagulation [D65], antiphospholipid syndrome [D68.61], malignant hypertension [I10, I15])

• Deceased

Results: As of July 31, 2023, there were a total of 142,046,930 living individuals registered in the database in the last 10 years. Of these, 560 individuals met eligibility criteria to define the TTP population (prevalence 0.0004% or 4 cases per million). Demographic characteristics included mean age at diagnosis (39.3 years [SD=14.3]), gender (73% female, 27% male), race (White = 44%, Black or African American = 33%, Asian = 3%, Other or unknown = 20%) and ethnicity (Not Hispanic or Latino = 73%, Unknown = 16%, Hispanic or Latino = 12%). Therapeutic interventions included systemic glucocorticoids (93% [prednisone 84%, methylprednisolone 68%, hydrocortisone 46%, dexamethasone 38%, triamcinolone 14%, betamethasone 9%, prednisolone 5%]), antithrombotics (86% [heparin group 79%, platelet aggregation inhibitors {excluding heparin} 29%, enzymes 27%, other antithrombotic agents {including caplacizumab} 18%, vitamin K antagonists 7%, direct factor Xa inhibitors 7%, direct thrombin inhibitors 2%]) and CD20 inhibitors (including rituximab) (40%).

Conclusion: This this is the first report to define and characterize a TTP population from a large US EHR database using a combination administrative codes and laboratory data. The study found a very low prevalence rate; that closely aligns with previously published estimates from registries of 4-5 cases per million for ITTP and 1-2 cases per million for CTTP. It was not possible to differentiate between CTTP and ITTP cases in this study due to a lack of ADAMTS13 genomic data. Demographic findings were consistent with previous registry data (median age of acute TTP presentation in the third to fourth decade of life, typically affecting females more than males). We found a high level of systemic glucocorticoid use as expected, but also high percentage of patients treated with rituximab in line with recent ISTH guidance. The authors are aware of other potential treatments in early development including gene therapy candidates for CTTP and cell therapy candidates for ITTP. This represents a tantalizing prospect for this population; however, to demonstrate efficacy and safety, these new therapies will require scientifically rigorous and well planned clinical studies including robust long-term follow-up.