Whether homocysteine 21.6umol/L is serious or not depends on the specific condition; a simple elevation is not serious, and the severity of the condition can increase if combined with cardiovascular disease. The normal value of homocysteine is 5.08umol/L to 15.39umol/L, and 21.6umol/L exceeds the normal value. Elevated homocysteine is a risk factor for cardiovascular disease and can increase the risk of atherosclerosis. Elevated homocysteine alone, if there are no other risk factors and the patient’s condition is not serious, can be controlled by lifestyle and eating foods rich in vitamin B, such as green fresh vegetables. For patients with elevated homocysteine levels, accompanied by definite cardiovascular and cerebrovascular disease, they are at high risk and their condition is more serious, based on dietary control, such as folic acid, vitamin B1 and vitamin B12. Patients with elevated homocysteine should be evaluated under the guidance of a physician to develop a specific treatment plan.