Validation study confirms prognostic value of MITS in TTP

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

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

TTP can take a congenital or acquired form, but in either case, it’s critical that patients receive treatment, the study authors noted.

“Untreated TTP is catastrophic, requiring early detection and rapid initiation of treatment to reduce mortality,” they said.

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

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

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

They used the National Inpatient Sample database to identify 4,589 people hospitalized with TTP between 2016 and 2019, then incorporated univariate and multivariate analyzes using metrics from MITS scores to see how well they correlated with prognosis.

Investigators found that women, white patients, and patients over 60 had higher all-cause mortality than their peers. They found that the variables included in MITS and the MITS score itself were correlated with mortality.

“Among the various clinical factors included in the study, arterial thrombosis and bleeding from the central nervous system have a [odds ratio] (3.17 and 2.93, respectively), thus associated with a poorer outcome compared to the other clinical variables included in the scoring scheme,” they noted. “This increased risk justifies the discrete value of 3 assigned to each clinical variable in the scoring system.”

Although they found MITS scores to be an effective prognostic tool, the authors said other metrics may also be useful. For example, they said parameters such as type of immunosuppression, comorbid conditions, and time from admission to first plasma exchange could be significant factors in determining patient risk. However, they said studying these parameters may require more data than is available in this dataset.

So far, they said their validation study shows that MITS can play an important role in guiding patient care.

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

Reference

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