Characterisation of Adult Patients with Primary Immune Thrombocytopenia and Positive Antiphospholipid Antibodies

Introduction: Primary immune thrombocytopenia (ITP) is a rare acquired autoimmune disease associated with a platelet count<100 G/L and a risk of bleeding, but also thrombosis [1] [2]. Positive antiphospholipid antibodies (aPL) are commonly reported among patients with ITP and have been associated with an increased risk of thrombotic events (TE) [3].

Method: The Vienna ITP Biobank is an ongoing prospective cohort study established in 2016. Adults with primary ITP are included, while patients with secondary ITP, hereditary thrombocytopenia, active malignancy, pregnancy, or a platelet count of≥100 G/L without treatment are excluded. Overall study design has been described in detail in previous publications [4] [5].

Patients with either positive lupus anticoagulant (LA) and/or antibodies against cardiolipin (aCL) and/or β₂ glycoprotein I (aβ2GPI) (aCL IgG≥10 U/mL, aCL IgM≥7 U/mL, aβ2GPI IgG≥8 U/mL, or aβ2GPI IgM≥8 U/mL) were classified as aPL positive and further classified as by degree of aPL positivity according to detected antibodies (single, double, or triple positive). Bleeding severity was assessed using the ISTH SMOG bleeding assessment tool (BAT) and the Vicenza bleeding score (BS).

Results: 180 patients with primary ITP, of them 111 female and 78 male, were analysed. They had a mean age of 50 years, and a median platelet count of 62 G/L. Among them, 25 patients (13.9%) had a history of TE (venous thromboembolism, myocardial infarction, ischemic stroke, peripheral ischaemia). 27 patients (15.0%) were classified as aPL positive. Most commonly, aCL IgM was positive, in 22 patients (12.2%), followed by aβ2GPI IgM in 14 (7.8%), aCL IgG in 6 (3.3%), and aβ2GPI IgG in 3 patients (1.7%). Positive LA was found in 7 patients (3.9%). 5 aPL positive patients had a history of TE, which did not differ significantly from aPL negative patients (p=0.54). aPL positive ITP patients also did not differ significantly in other variables, such as platelet count, antiplatelet antibodies (aPLT), treatment history, or bleeding scores. Detailed results are outlined in [Fig. 1]. In uni- and multivariable logistic regression ([Fig. 2]), aPL positivity was significantly associated with age (odds ratio [OR] 1.03, 95% confidence interval [CI] 1.00–1.05), while sex, platelet count, history of TE, and aPLT, as well as bleeding scores were not significantly associated. Neither aPL positivity nor the degree of aPL positivity was significantly associated with a history of TE.

Fig. 1  Clinical patient characteristics and laboratory results. Patients with positive and negative aPL were compared. Students t-test was used for normally distributed data, Wilcox rank sum test was used for non-normally distributed data. Χ²-test was for categorical data, Fisher’s exact test was used for sample sizes≤5. P-values of<0.05 were considered significant. Abbreviations: SD – standard deviation; IQR – interquartile range; GP – glycoprotein.

Fig. 2  Uni- and multivariable regressions were used to determine the odds ratio (OR) and 95% confidence interval (CI) for aPL positivity and for a history of thrombotic events (TE) and adjusted for age and sex. P-values of<0.05 were considered significant.Abbreviations: CI – confidence interval; TE – thrombotic event; BAT – bleeding assessment tool; BS – bleeding score.

Conclusion: In this cohort, ITP patients with positive aPL did not significantly differ from aPL negative patients in regards to their clinical characteristics or laboratory results. However, age was found to be significantly associated with aPL positivity. Interestingly, patients with positive aPL did not have a higher frequency in history of thrombotic events. Prospective analyses with larger sample sizes are required to better assess individual risk of thrombosis in patients with positive aPL.

Publikationsverlauf

Artikel online veröffentlicht:
13. Februar 2025

• References

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