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Can I Drink Alcohol the Night Before a Blood Test?

One of the investigation methods for the presence of any disease is blood test. It is also useful in tracking conditions like cholesterol and diabetes. The most frequently used investigation process for any health condition is a blood test.1 There are certain things which should be taken care of before going for a blood test. A question that often arises before a blood test is whether one can consume alcohol or not.

Can I Drink Alcohol The Night Before A Blood Test?

Can I Drink Alcohol The Night Before A Blood Test?

The answer to this question is a no.

Effects of Drinking Alcohol: Why You Must Avoid Drinking Alcohol The Night Before A Blood Test?

Distribution of alcohol in the body of an individual depends upon the fat content and water in the body. Though alcohol is not soluble in water, it can penetrate the plasma membranes and pass through them just by simple diffusion. Then according to the percentage of water present in tissues and cells, alcohol is distributed to different parts of the body through blood stream.

Before knowing the effect of alcohol on the test results, it is important to know the metabolism of alcohol in the body. Basically, there are two enzymes which are responsible for metabolism of alcohol. 2 They are ADH (alcohol dehydrogenase) and ALDH (aldehyde dehydrogenase.)3 As the name itself indicates, the first enzyme breaks down alcohol into an aldehyde known as acetaldehyde. It is immediately converted into another substance called acetate with the help of second enzyme because acetate is less toxic than acetaldehyde. The main purpose of this conversion is to eliminate acetaldehyde as it is highly toxic and is known to cause cancer (carcinogen). Afterwards, this acetate is broken down into carbon dioxide and water in all the other tissues4.

There are two more enzymes which act upon alcohol and convert into acetaldehyde. One is CYP2E1 (cytochromeP450 2E1) which works even if the person consumes more quantity of alcohol. The other enzyme is catalase works only when a small quantity of alcohol is present1. Even a little alcohol is found in the body, it is removed by the reaction of fatty acids with alcohol. During this reaction another compound called FAEEs (fatty acid ethyl esters) are formed which damages the pancreas and liver.

Since alcohol decreases the activity of CNS (central nervous system) it is considered as a depressant. From some researches acetaldehyde produced in brain by the action of CYP2E1 and catalase on alcohol is found to cause impaired coordination, sleepiness and influence on memory also. Some argue that there will not be sufficient amount of acetaldehyde in the brain to cause these effects. However, they use fatty acids for the reaction and hence influence on blood tests. The other effects of alcohol metabolism on the components of blood are:

Normal gluconeogenesis is disturbed due to conversion of pyruvic acid into lactic acid. It leads to acidosis and hypoglycemia.

The fats are not oxidized and hence may be accumulated in the liver. Fats intern are liberated into the blood stream. This increases the concentration of fat in blood and also may be a risk factor of cardiac arrest.

The people who started consuming alcohol in large quantity will be overweight because of production of fatty acids.

Uses of Blood Tests

Blood tests confirm many diseases. In some cases though the results cannot confirm the disorders at least they guide the health professionals to move further by following some other procedures in the investigation process. Blood tests help in:

  • Diagnosing the diseases like coronary heart diseases, cancer, AIDS and diabetes
  • Measuring the bleeding time and clotting time
  • Tracking the effect of medicines on the body
  • Finding out the health condition of organs like liver, kidneys and heart
  • Measuring the levels of several hormones in the blood
  • Detecting anemia by observing the quantity of hemoglobin
  • Monitoring the condition of patients in case of chronic disorders.
  • Different Kinds of Blood Tests Usually Ordered
  • Blood tests to know the risk of cardiac diseases
  • Analysis of enzymes and their function in the blood
  • Blood test to measure the number of RBC, WBC and platelets which is known as CBC or complete blood count
  • Test to know the chemical composition of the blood.

Things to Follow Before Blood Test

Some blood tests are to be done while fasting. The duration of fasting depends upon the kind of blood test. Some tests require fasting for 8 to 10 hours, some 10 to 12 hours. This is because the components of food vary the composition of the blood which leads to wrong results.

  • Water is not avoided before a blood test. Intake of water becomes advantageous as it increases the volume of blood and keeps the veins in hydrated state. Then it would be easier for the technician to take the blood. Actually the workers of the lab suggest the drinking of water before testing.
  • Some doctors do not advice the patients to take medicines during the period of blood testing thinking that they have bad impact on the test results.
  • Intake of caffeinated drinks is prohibited before the test.
  • Alcohol is found at least in traces in the blood for many days after consumption. Hence the patient is advised to stop drinking alcohol 24 hours before going to test.


Alcohol has both positive and negative effects on humans. The positive effect makes it to be used as a drug which alters the mood and helps to forget the sorrows. At the same time, it has negative effect on the body as it causes addiction and also acts as a depressant. It also influences the result of blood test as it is found in more concentration in blood. Measurement of fats and glucose would be varied and it misguides a doctor in the process of diagnosis and treatment.


  1. “Venipuncture – the extraction of blood using a needle and syringe”. Retrieved June 21, 2012.
  2. https://pubs.niaaa.nih.gov/publications/aa72/aa72.htm
  3. Alcohol Research & Health, Vol. 29, No. 4, 2006: This issue describes alcohol’s metabolic pathways, their genetic variation, and the effects of certain byproducts, such as acetaldehyde, on a range of organs and tissues.
  4. Alcohol Research & Health, Vol. 30, No. 1, 2007. This issue examines how differences in metabolism may lead to increased or reduced risk among individuals and ethnic groups for alcohol-related problems such as alcohol dependence, cancer, fetal alcohol effects, and pancreatitis.
Sheetal DeCaria, M.D.
Sheetal DeCaria, M.D.
Written, Edited or Reviewed By: Sheetal DeCaria, M.D. This article does not provide medical advice. See disclaimer
Last Modified On:October 29, 2019

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