Thrombocytopenia and thrombocytosis are associated with different outcome in atrial fibrillation patients on anticoagulant therapy

Background
Information regarding the significance of platelet (PLT) count on outcome of atrial fibrillation (AF) patients who are treated with anticoagulants is limited.
Methods
We conducted a monocentric observational retrospective cohort study of AF patients treated with either warfarin (n = 6287) or non-vitamin K antagonist oral anticoagulants (NOACs) (n = 5240). Patient were divided into 3 subgroups; low, normal and high PLT for counts < 150 K/ μl, 150–450 K/ μl and > 450 K/ μl, respectively. A multivariate Cox-regression was used to evaluate the association between PLT subgroups and clinical outcomes.
Results
During follow-up [median = 40.6 months (IQR 17.6–60)], mortality (HR 1.36, 95 CI 1.1–1.74, p = 0.01) and rate of myocardial infarction (MI) (HR 2.4, 95 CI 1.28–4.57, p = 0.007) were higher in patients with high compared to normal PLT. Transient ischemic attack or cerebrovascular accident (TIA/CVA) rate was lower in patients with low compared to normal PLT (HR 0.69, 95 CI 0.51–0.93, p = 0.02). A comparison between NOACs and warfarin demonstrated a significantly better clinical outcome for patients on NOACs in both the low (lower mortality rates) and normal PLT subgroup (lower mortality, TIA/CVA and systemic emboli rates). For patients on NOACs, low and high compared to normal PLT were associated with a higher combined outcome (HR 1.12, 95 CI 1–1.38, p = 0.047), and a higher systemic emboli rate (HR 7.07, 95 CI 1.66–30.25, p = 0.008), respectively.
Conclusions
Abnormal PLT count is associated with different clinical outcome of AF patients on anticoagulants. Further studies are needed in order assess whether PLT level should influence strategies of anticoagulation.