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International committee aims to standardize terms for ITP
International Working Group sets new definition for response, threshold for diagnosis.
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An International Working Group of 20 physicians from institutions in the United States, Europe and Australia has released a report with the hopes of standardizing definitions and usages for terms used in treating immune thrombocytopenic purpura.
The group met in 2007 during a two-day structured meeting, the Vicenza Consensus Conference in Vicenza, Italy. Over time, the physicians reached consensus and unanimously agreed to the terms and definitions in their report.
They started by changing the name of the condition to immune thrombocytopenia, writing that the term “purpura” was inappropriate, “because bleeding symptoms are absent or minimal in a large proportion of cases.” Donald M. Arnold, MD, an assistant professor of medicine at McMaster University in Hamilton, Ontario and a member of the International Working Group, said the term “idiopathic thrombocytopenic purpura” was simply inaccurate.
“We don’t really think it’s idiopathic, because that essentially means we don’t have any clue what causes it,” he said. “We think it’s mostly an immune mediated cause, and immune was another word that people would substitute for that initial ‘I.’ But no one ever decided to use immune instead of idiopathic. To be frank, it is arbitrary that this group decided the name should be immune thrombocytopenia, but it just goes to show there is a lack of consensus even on the name of the disease itself.”
The working group members specifically chose to retain the abbreviation “ITP” because of its familiarity and for the purposes of literature search. The group also decided to lower the threshold for diagnosis from a platelet count of less than 150 × 109/L to a count of less than 100 × 109/L. Arnold said the new threshold is better supported by science.
“Once the group decided to standardize definitions, we chose to establish definitions that make the most sense,” he said. “The cutoff of 150 × 109/L is widely adopted in many laboratories, but there is more evidence to support saying a patient with a platelet count of less than 100 × 109/L has ITP.”
One reason the group decided to develop standard definitions was the difficulty in comparing trial results. The working group wrote that differences in “study designs and endpoints, as well as the heterogeneous mechanisms of action and patterns of response to the various investigational treatments,” along with a lack of description of key features, such as patient-related parameters, make it difficult to compare clinical response rates and draw definitive conclusions. The same holds true for studies involving children, they said, especially when it comes to endpoints and definition of outcomes.
“There’s certainly a lot of value in the older trials,” Arnold said. “But when it comes to pooling the data or comparing one study to another, it’s difficult to do if you’re not speaking the same language.”
Arnold said there is a push to standardize the language around ITP now because new pharmacological agents are being introduced leading to an unprecedented “explosion” of clinical trials in ITP.
“The importance of this paper is not so much the actual definitions, though certainly that is part of it, but it’s an attempt to make the methodology more rigorous,” he said. – by Jason Harris
Rodeghiero R. Blood. 2009;113:2386-2393.