The blood test that is used to measure alcohol plasma levels is also called the blood alcohol test. This is a test that is used along with the breathalyzer test to measure the amount of alcohol in the blood as a legal requirement. This test is not one of the tests that are conducted during a standard blood donation exercise though it is highly advised that you one doesn't drink one's self into a stupor before donating blood. Drinking alcohol after donating plasma or blood in general is not advised. This is because the blood pressure might dip slightly after the 500 ml loss of blood that takes place and therefore could end up accentuating any loss of consciousness and if you are driving or operating any heavy machinery could cause an accident.
The blood alcohol level test is usually done to confirm the findings of the standard breathalyzer test. This is a test that is usually administered on suspected driving under the influence of intoxicating substance cases. It is a legal requirement in nearly all countries and especially so in those countries that have a zero tolerance for drinking and driving.
There is no preparation that you have to make for this test though if the person that is administering has suspected you of being drunk but you haven't had anything to drink, and you are also diabetic, this is a sign of danger for you. In hospitals, it is a common mistake to misinterpret ketoacidosis with alcohol poisoning. In this case, you must ensure that you inform the law enforcement officer and health care professional that you are diabetic and rush to the hospital immediately.
The test is conducted much like any other blood test is with a rubber tube wrapped around your arm, the doctor feeling for a vein, and the blood being drawn. The levels that are usually considered unsafe start from as low as 0.02% as 0.2% is sometimes considered adequate for some people to lose consciousness. The highest recorded levels were of a person wheeled into an emergency room. His levels were at 0.9%, a level that should have killed him. The hospital staff had to recheck their equipment a few times for malfunction before finally accepting that they had a case of the World Record for the highest blood alcohol levels in recorded medical history. The patient did survive the alcohol and was discharged the next day.