Context: Subclinical hypothyroidism (SH) is associated with some abnormalities in primary and secondary haemostasis.Objective: To evaluate changes in primary and secondary haemostasis induced by Levothyroxine (L-T4) treatment in SH patients.Design: Prospective cohort study with a 6-months follow-up.Study Setting: Outpatients referred to "Federico II" University of Naples.Patients: Subjects with a SH without previous/ongoing L-T4 therapy.
Main OutcomeMeasure: Changes in major haemostatic/fibrinolytic variables and platelet reactivity (mean platelet volume [MPV], arachidonic acid [AA] or adenosinediphosphate [ADP] concentrations inducing a Ն50% irreversible aggregation [AC-50%]) in SH patients before and after a 6-month L-T4 treatment. Results: At baseline, 41 SH patients showed higher levels of FVII activity (123.9Ϯ20.4 vs 107.7Ϯ12.2, pϽ0.001), PAI-1 (33.6Ϯ13.9 vs 22.5Ϯ5.74, pϽ0.001) and t-PA (5.56Ϯ2.22 vs 4.75Ϯ1.61, pϭ0.010), with lower levels of D-Dimer (220.3Ϯ67.1 vs 252.1Ϯ72.4, pϭ0.017) compared with healthy controls.SH patients also showed a higher MPV (9.92Ϯ1.15 vs 8.9Ϯ0.9, pϽ0.001) and AC-50% to AA (0.18Ϯ0.12 vs 0.36Ϯ0.10, pϽ0.001) and to ADP (1.5Ϯ0.6 vs 1.9Ϯ1.3, pϭ0.024). After a 6-month L-T4 therapy, a reduction of FVII activity (from 123.9Ϯ20.4 to 102.6Ϯ14.3, pϽ0.001), PAI-1 (33.6Ϯ13.9 to 19.4Ϯ7.6, pϽ0.001) and t-PA (5.56Ϯ2.22 to 1.91Ϯ4:43, pϭ0.002) was found in SH subjects, with a marginal increase in D-Dimer (from 220.3Ϯ67.1 to 245.2Ϯ103.1, pϭ0.053). AC-50% to AA (from 0.18Ϯ0.12 to 0.54Ϯ0.3, pϽ0.001) and to ADP (from 1.5Ϯ0.6 to 1.86Ϯ0.3, pϭ0.042) were reduced, paralleled by a significant reduction of MPV (from 9.92Ϯ1.15 to 9.10Ϯ1.23, pϭ0.016).Conclusions: SH patients exhibit a pro-thrombotic status which is reverted by a 6-month L-T4 treatment.