Introduction: Romiplostim is a thrombopoietin receptor agonist used as a second-line treatment for primary immune thrombocytopenia (ITP). Its early use is becoming increasingly common due to its non-immunosuppressive properties and favorable toxicity profile. However, one major limitation is the indefinite duration of therapy, as there are currently no established clinical parameters for its discontinuation. In 2023, the European Delphi consensus panel was established to agree on discontinuation guidelines. Stable platelet counts >100,000/μl with a minimum of six months of treatment represent the only clinical condition for unanimous agreement among experts. This situation necessitates exploration of under-studied areas such as laboratory markers including the Immature Platelet Fraction (IPF%).

Objectives:To evaluate the IPF% test as a potential marker for Romiplostim discontinuation in patients over 15 years of age with immune thrombocytopenia treated at a tertiary-level hospital in Cuenca (Ecuador) between August 2015 and May 2023.

Study Design and Participants: -Population: Included patients were diagnosed with ITP in any of its phases (newly diagnosed, persistent, or chronic), as well as those with secondary immune thrombocytopenia due to systemic autoimmune diseases (e.g., systemic lupus erythematosus or SLE). Exclusion criteria included pediatric patients (under 15 years of age) and those with secondary immune thrombocytopenia related to oncologic or oncohematologic diseases.

-Study Design: This was a descriptive, retrospective, non-longitudinal study with incidental non-probability sampling. Data were obtained from digital medical records.

-Laboratory Procedure: IPF was measured using a Sysmex analyzer, with the reference range estimated between 0.7–5.7%. Measurements were taken at two time points: prior to initiating Romiplostim and either after its discontinuation or at some point during ongoing treatment.

-Statistical Analysis: Chi-square and Student's t-tests were used for comparisons between independent groups, while the Wilcoxon signed-rank test was applied for paired samples. Survival analyses were performed using the Kaplan-Meier method, and differences between groups were assessed using the log-rank (Mantel-Cox) test.

Results: -The study included 23 patients treated with Romiplostim for immune thrombocytopenia. The mean age was 48.3 years (95% CI: 39.86–57.01), with a median age of 50 years, multimodal distribution, and variance of 393,075. Patient ages ranged from 17 to 90 years. Fourteen patients (60.9%) were female.

-Five patients (21.7%) achieved treatment-free remission after a mean Romiplostim duration of 16.3 months (95% CI: 5.7–19).

-In bivariate analysis, a statistically significant association was observed between the grouping variable (Romiplostim discontinuation) and treatment duration (P = 0.036). (KS test = 0.200; Levene's test = 0.075).

-IPF% was measured both at baseline and at follow-up in 16 of the 23 patients. The mean baseline IPF% was 19.6% (95% CI: 14.4–25.8), while the mean post-treatment IPF% was 13.5% (95% CI: 6.9–20.1).

-In paired analysis, a statistically significant difference was found between baseline and post-treatment IPF% values (P = 0.015). (KS test for baseline IPF = 0.011; post-treatment IPF = 0.025).

-A univariate logistic regression was performed using “Romiplostim discontinuation” as the dependent variable and “baseline IPF%” and “post-treatment IPF%” as independent variables. No statistically significant results were found to justify a subsequent multivariate regression.

-In survival analysis, “Romiplostim discontinuation” (event) was compared with other variables without statistically significant results (P = 0.960).

Conclusions: -The duration of treatment with sustained platelet counts remains the only consensus variable currently available for considering Romiplostim withdrawal. There is a need to identify additional clinical or laboratory variables to guide successful discontinuation and prevent rebound thrombocytopenia.

-IPF% may serve as a potential laboratory predictor for Romiplostim discontinuation (P = 0.015); however, larger-scale studies are required, along with standardization of reference ranges due to the variability of this parameter.

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2025
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