Similarly, it has also been shown that salivary xanthine oxidase takes part in biochemical reactions during the occurrence of ischemia–reperfusion; its activity is used with very high specificity and sensitivity as a biomarker for the diagnosis of ischemic and hemorrhagic stroke, and its functional status [64] also plays an accuracy role in distinguishing mild-to-moderate cognitive decline. This evidence concerns the gene XDH and hemorrhagic stroke.