Validation Study Affirms Prognostic Value of MITS in TTP

Investigators said the Mortality in TTP Score (MITS) was effective at characterizing the risk of death in patients hospitalized with thrombotic thrombocytopenic purpura (TTP).

The prognostic tool used to calculate the risk of mortality among hospitalized patients with thrombotic thrombocytopenic purpura (TTP) is effective at characterizing individual patient risk of death, according to what is believed to be the first external validation study of the tool.

This report, published in Transfusion Medicine, found the Mortality in TTP Score (MITS) had an area under the receiving operator character curve of 71%, which was similar to the 78.6% reported in the original derivation study.

TTP can come in either congenital or acquired form, but in both cases, it is essential that patients receive treatment, noted the study authors.

“Untreated TTP is catastrophic, requiring early recognition and prompt treatment initiation to decrease mortality,” they said.

Historically, therapeutic plasma exchange has been the go-to therapy for the disease, which is characterized by a deficiency of the von Willebrand factor cleaving protease, ADAMTS13. However, in recent years, the authors said the anti–von Willebrand factor nanobody caplacizumab (Cablivi) has become the first-line therapy for many patients.

What has not changed, however, is the need to quickly identify high-risk patients. The MITS system was originally developed to predict hospital mortality in patients undergoing plasma exchange therapy. The scoring tool incorporates factors such as platelet transfusion, cerebral ischemia, intracranial hemorrhage, age, and renal failure, among others. Patients with high scores despite plasma exchange may warrant further treatment, such as with caplacizumab, the authors said.

Still, although MITS has become an important part of treatment since it was first unveiled in a 2016 study, no one has yet undertaken an external validation study to confirm the tool’s efficacy, the investigators said.

They used the National Inpatient Sample database to identify 4589 people hospitalized with TTP between 2016 and 2019, and then incorporated univariate and multivariate analyses using the parameters in MITS scores in order to see the degree to which they correlated with prognosis.

The investigators found women, White patients, and patients older than 60 years had higher all-cause mortality than their peers. They found that both the variables included in MITS and the MITS score itself correlated with mortality.

“Of the various clinical factors included in the study, arterial thrombosis and central nervous system bleeds carry a higher [odds ratio] (3.17 and 2.93, respectively), thereby associated with a poorer outcome when compared to other clinical variables included in the scoring schema,” they noted. “This increased risk justifies the discrete value of 3 assigned to each clinical variable in the scoring system.”

Although they found that MITS scores were an effective prognostic tool, the authors said other parameters might also be helpful. For instance, they said parameters like type of immunosuppression, comorbid conditions, and the time between admission and the first plasma exchange might be meaningful factors in determining patient risk. However, they said investigating those parameters might require more data than were available in this data set.

Until then, they said their validation study shows MITS can play an important role in guiding patient care.

“The existence of highly effective treatment modalities in an otherwise life-threatening disease warrants early risk stratification to prevent mortality, and MITS is a valuable clinical tool that may guide that process,” they concluded.


Andanamala H, Brunton N, Pai R, Sostin O. A second look at the mortality in thrombotic thrombocytopenic purpura score: an external validation study. Transfus Med. Published online January 27, 2023. doi:10.1111/tme.12956

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