Patients with high blood pressure can donate blood if their systolic blood pressure is 90-140mmHg and diastolic blood pressure is 60-90mmHg, but they should be cautious about donating blood if their systolic blood pressure is 140mmHg or more, or if their diastolic blood pressure is 90mmHg or more. Because the volume of blood donated is about 200-400mL, blood pressure may rise too fast or too high due to pain or fear, resulting in dizziness and other uncomfortable symptoms. It is also unsuitable for patients with high blood pressure to donate blood if their blood pressure is below 90/60mmHg due to overdose of medication or other reasons, as this may lead to shock and other malignant conditions.