Knowledge Check

Which of the following statement(s) is/are correct:

20019 Standardization of terminology, definitions and outcome criteria in immune thrombocytopenic purpura of adults and children: report from an international working group:

Why we use the threshold platelet count of < 100 x 10⁹/L to define ITP:

Stasi et al. Long-term outcome of otherwise healthy individuals with incidentally discovered borderline thrombocytopenia. PLoS Med. 2006 Mar;3(3):e24.

• Prospective study of 260 apparently healthy individuals with incidentally discovered platelet counts between 100 x 10⁹/L and 150 x 10⁹/L were monitored for 6 mo to determine whether their condition persisted.
• The monitoring period was completed in 217 cases, of whom 191 (88%) maintained stable platelet counts; these 191 individuals were included in a long-term follow-up study to gain knowledge of their natural history.
• The 10-y probability of developing idiopathic thrombocytopenic purpura (ITP), as defined by platelet counts persistently< 100 x 10⁹/L, was 6.9% (95% confidence interval [CI]: 4.0%–12.0%).
• The 10-y probability of developing autoimmune disorders other than ITP was 12.0% (95% CI: 6.9%–20.8%).

Bottom line: patients with platelet counts 100-150 x 10⁹/L rarely develop more severe thrombocytopenia when followed longitudinally. Therefore, they are not labeled with the diagnosis of immune thrombocytopenia (ITP).