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Thrombus
New research suggests a scoring system can predict the risk of thrombosis in patients with immune thrombocytopenia (ITP) who are taking anticoagulants.
Researchers tested their Thrombosis and Thrombocytopenia (TH2) risk assessment score in a small group of ITP patients on anticoagulants, and the score identified all seven patients who developed thrombosis.
The researchers also found that patients’ TH2 scores changed quickly—within a matter of days—which suggests they should be re-evaluated for thrombosis risk frequently.
Amaris K. Balitsky, MD, of McMaster University in Hamilton, Ontario, Canada, and her colleagues detailed this research in Blood.
About the score
To develop the TH2 score, the researchers conducted a review of the literature and existing tools used to assess the risk of thrombosis and bleeding. The resulting score consists of two thrombosis items and two bleeding items.
The thrombosis items are:
- High thrombotic risk, which includes patients with atrial fibrillation and a CHA2DS2-VASc score greater than five; unprovoked, recurrent, or cancer-associated thrombosis; or antiphospholipid antibody syndrome
- Receipt of ITP therapies known to increase the risk of thrombosis in the previous 14 days or splenectomy in the previous 30 days.
The score’s bleeding items are:
- Platelet count less than 20 x 109/L
- Major bleeding (grade 2 bleeding that does not involve the skin) observed at a clinical encounter.
Each thrombosis item is assigned a score of +1, and each bleeding item is assigned a score of -1. A positive score or score of 0 suggests a net increased risk of thrombosis, and a negative score suggests a net increased risk of bleeding.
Patient population
The researchers tested the TH2 score in patients enrolled in the McMaster ITP Registry from 2010 to 2017.
There were 314 patients enrolled, but only 13 were receiving anticoagulation and had a platelet count less than 50 x 109/L. Six of these patients were receiving anticoagulation for atrial fibrillation and seven for venous thrombosis. Four patients were taking antiplatelet agents as well.
The median follow up was 9 months (interquartile range, 4.5 to 24 months). During that time, there were 41 clinical encounters. Data on treatment decisions and clinical outcomes were available for 32 of these encounters.
Ten of the 13 patients had anticoagulation withheld at some point during their 22 clinical encounters. Major bleeding was present at five of the encounters. At 17 encounters, patients received additional ITP treatments.
Six of the 10 patients who stopped anticoagulation had new thrombotic events, and two of these events were fatal. Three of the patients had thrombotic events even though they resumed anticoagulation.
The remaining three patients (of the 13) did not stop anticoagulation. These patients received additional ITP treatments at six of their 10 clinical encounters.
Major bleeding was present at two of the 10 encounters, and one new thrombotic event occurred in a patient with metastatic squamous cell cancer (despite continued treatment with warfarin).
Testing the score
The TH2 score accurately predicted all seven thrombotic events.
There were four patients who initially had a negative TH2 score, which suggested an increased risk of bleeding.
However, these patients had a positive or 0 score—suggesting an increased risk of thrombosis—when they were assessed again, after their platelet counts increased above 50 x 109/L.
The remaining three patients had initial scores of 0 and subsequent positive scores, both suggesting an increased risk of thrombosis.
The researchers said these findings suggest patients should be re-evaluated for thrombosis risk frequently, as ITP treatments are given and platelet counts increase.
“The results of our study suggest that the risk of thrombosis is high in patients with ITP who have a separate indication for anticoagulation, especially after ITP therapies are administered and the severe thrombocytopenia improves,” the researchers wrote. “Early resumption of anticoagulation should be considered in this population.”
The researchers also noted that this study was limited by its retrospective, single-center design and the small number of patients evaluated. Therefore, the TH2 score should be validated in additional, larger studies.
One researcher reported relationships with Amgen, Novartis, Rigel Pharmaceuticals, UCB, and Principia Biopharma. The other researchers said they had no competing financial interests.