Association of neutrophil-to-lymphocyte ratio and thrombotic events in US veterans with polycythemia vera.

6578 Background: Neutrophil-to-lymphocyte ratio (NLR) is a novel predictor of thrombosis in patients with Polycythemia Vera (PV), an uncommon myeloproliferative neoplasm distinguished by excessive red blood cell production within the bone marrow. However, there is no guideline-endorsed NLR cut-off that mandates cytoreduction. This study aims to assess the association of NLR and risk of thrombotic events, and evaluate the impact of different therapies based on electronic health records from the United States (US) Veterans Affairs Healthcare System (VAHS). Methods: Veterans with PV were identified based on either 2 outpatient codes separated by 30 or more days or 1 inpatient code in the VAHS databases (2017–2023). The first PV diagnosis was considered as the index date. Patients with myelofibrosis or leukemia diagnosis before the index date were excluded from the analysis. Veterans with at least one NLR value were examined for the occurrence of thrombotic events. Baseline characteristics were defined over the two-year period preceding the first PV diagnosis code. Treatments were defined within two years of the index date and categorized as: cytoreductive therapy (including hydroxyurea, interferons, or ruxolitinib), phlebotomy interventions, or neither. Cox proportional hazards regression was used to evaluate the associations between therapies and the risks of thrombotic events, controlled by the pre-index use of individual therapy. Results: A total of 11,809 Veterans with PV were identified from the VAHS, with a mean (SD) age of 67.4 (11.1) years, 96.7% male, 9.0% Black, 81.1% White, and 5.1% Hispanic. The rate of thrombotic events (per 1000 person-year) was 45 for patients treated with cytoreductive therapy, 32 for phlebotomy-treated patients, and 51 for those who received no treatment. Patients were delineated into five groups based on NLR: <1, 1-2.9, 3-4.9, 5-19.9, and above 19.9. The rate of thrombotic events was closely at 39% amongst each group with NLR below 5. For those with NLR at 5-19.9 and >19.9, thrombotic events were reported in 48% and 61% of veterans, respectively. Cytoreductive therapy and therapeutic phlebotomy were each associated with significantly lower risks of thrombotic events compared to none of these two treatments among PV patients. Adjusted risk of thrombotic events was 45% (HR: 0.55, 95%CI: 0.48-0.62, P < 0.01) and 34% (HR: 0.66, 95%CI: 0.57-0.78, P: < 0.01) lower for patients with cytoreductive and phlebotomy therapy compared to no treatment. Conclusions: The real-world evidence from VAHS yields a cut-off value of NLR at 5 to predict risks of thrombotic events among Veterans with PV. Patients receiving cytoreductive therapy or therapeutic phlebotomy had reduced risk of thrombotic events.