Background. Migraine is diagnosed based on the International Headache Society (IHS) criteria, all of which are subjective complaints. Endothelial dysfunction and altered vasomotor reactivity have been implicated in migraine pathophysiology, which has been objectively studied as reduced breath-holding index (BHI) in migraineurs. We aimed to validate the migraine vascular index (MVI), derived from transcranial Doppler (TCD) measurements during breath-holding (hypercapnia) and hyperventilation (hypocapnia), as a more objective tool to differentiate migraine from other primary headaches.Methods. This prospective cohort study enrolled outpatients with primary headaches in Jakarta, Indonesia. Migraine was confirmed using the Indonesian version of the IHS criteria (MS-Q) with a score of≥ 4, a positive breath-holding index (BHI), and/or a positive therapeutic response following one month of topiramate administration. The MVI was independently measured using TCD by comparing the vasodilation (breath-holding) and vasoconstriction (hyperventilation) flow responses in the middle cerebral artery.Results. Of 128 patients, 104 and 24 were confirmed to have migraine and non-migraine headache, respectively. Compared with non-migraineurs, migraineurs had significantly lower median BHI (0.70 vs. 1.53; p< 0.001) and MVI (0.49 vs. 1.45; p< 0.001), indicating greater impairment of vasomotor reactivity. Using previously reported cut-off values of MVI 1.035 and BHI 0.69, ipsilateral MVI showed better diagnostic performance than ipsilateral BHI (AUC 92% vs. 70%) for identifying migraine.Conclusion. MVI demonstrates high diagnostic accuracy …