Natural history of untreated adult Immune Thrombocytopenia (ITP)

Background: International guidelines recommend that patients with Immune thrombocytopenia (ITP) presenting platelets > 30x109/L should be followed-up without treatment. However, data on clinical courses and risk factors are limited. Objective: To determine the natural history and prognostic factors of untreated ITP. Materials and Methods: This retrospective cohort included adult ITP patients (platelet count 30-149 x109/L) at King Chulalongkorn Memorial Hospital from January 2015 to October 2022. Treatments were provided only to patients with platelet counts < 30x109/L and/or major bleeding. Results: A total of 73 patients were included. The mean age was 62 ± 16.64 years, and 56% were female. The median follow-up time was 3 years, comprising 272.48 patient-years. Seventeen patients (23.3%) subsequently required treatments, with an incidence rate of 6.24% per year (95% Confidence interval [CI], 3.88-10.0%). In multivariate analysis, risk factors for requiring treatment were age < 35 years (adjusted hazard ratio [aHR] 3.93; 95%CI, 1.27-12.22, P = 0.018) and a maximum-minimum platelet count during follow-up (excluding counts at treatment initiation) ≥ 70x109/L (aHR 2.89; 95%CI, 1.02-8.23, P = 0.047). Baseline platelet count did not predict outcomes, but persistently maintaining platelet counts >100 x 109/L for more than 3 or 6 months was associated with better prognosis. No severe bleeding related to thrombocytopenia was observed. The spontaneous recovery rate was 10% with an incidence of 2.57% per year (95%CI, 1.22-5.93%). Conclusions: The majority of untreated ITP patients had a good prognosis. Adverse risk factors included younger age and wide fluctuations in platelet counts.