Homocysteine is a blood test that is a sensitive indicator of vascular damage. Homocysteine is a metabolite of cysteine and methionine and a sulfur-containing acid. Homocysteine belongs to the group of blood tests whose specimen type is serum. Under normal circumstances, the reference range of homocysteine is 5.08~15.39 μmol/L, which can generally be used as an indicator to determine vascular damage. In addition to this, in clinical practice, when homocysteine is elevated, it may lead to diseases such as atherosclerosis, stroke, and dementia. To summarize, if a patient’s homocysteine result is abnormal, further examination is needed to clarify the specific cause.