It depends on the type of blood test you’re having. The healthcare professional who arranges your blood test will tell you whether there are any specific instructions you need to follow before your test. You can eat and drink as normal before some blood tests. In other cases, you will be instructed not to eat or drink (other than water) before your test. This is known as a fasting blood test. You may also be told not to drink alcohol or not to smoke before your test.