#glucose #general blood analysis #hormones

Why Are Blood Tests Taken On an Empty Stomach?

28 octobre 2025

2 min de lecture

Ouvrir le guide Ouvrir la collection Ouvrir la série

Is it possible that this is just something doctors like to do for no good reason? And why should you fast before taking a blood test?

Points clés

Is it possible that this is just something doctors like to do for no good reason?
What is "fasting?”
When is it especially important?

Pour qui

Ceux qui explorent Blood à travers glucose, general blood analysis.

Pourquoi c'est important

Cet article vous aide à vous orienter rapidement, puis à passer à une collection ou une série si vous souhaitez aller plus loin.

Auteur de l'article

Dr. Helga

General practitioner

What is "fasting?”

Fasting before a blood test means that you should not eat or drink anything but water for 8 to 12 hours before the blood test. Even a small spoonful of sugar in a cup of tea will change the blood glucose reading: the blood sugar level will be high and the doctor will not know why and which ruins the test.

The same is true for cholesterol, bilirubin, and some other indicators. Simply put, on an empty stomach means "as is," without any foods or liquids other than water. Doctors need to understand how the body behaves without external stimulation.

By the way, this is why we also recommend not smoking or drinking alcohol for at least 12 hours before the analysis (even better is abstaining for 24–48 hours beforehand, as toxic substances and their decay products can greatly distort test results.

According to the World Health Organization (WHO), laboratory tests provide 60 to 80 % of diagnostic information about a patient.

When is it especially important?

Blood tests must be taken on an empty stomach to determine lipid profile parameters including cholesterol, HDL, LDL, and triglycerides. Any ingestion of food or drink will skew the data. General blood tests are not so severe: it is enough to refrain from eating and drinking an hour before taking the test.

However, you should abstain from fatty foods for 12 hours or more: fats in the intestines turn into chylomicrons, which make the blood "turbid," or, as doctors will tell you, what turns into cholesterol. Such a sample will be rejected by the lab technicians, and you will have to take the test again. The day before you should exclude butter, mayonnaise, fatty meats, sausages, and cheeses from your diet.

Some tests, especially those for hormones, are important to take at a specific time of a day or menstrual cycle. For example, somatotropic hormone (STH), cortisol, and adrenocorticotropic hormone (ACTH) can vary in concentration by 2–4 times depending on whether you take the test in the morning or evening.

What if I'm taking medication?

Ideally, you shouldn't interrupt a course of medication for the sake of a test. However, you need to inform your doctor ahead of time about what medications you are taking so that he or she can take into account the potential impact of the medication when deciphering the data. If it is possible to stop taking pills for 1–2 days, it is a good idea to do so (in consultation with your doctor).

Continuer la lecture

Blood#malaria

Defeating Malaria for Good: Scientists Are Optimistic

Researchers have identified how natural human antibodies can block the entry of malaria parasites into red blood cells. This is a key step towards ending malaria in the world.

Darya28 oct. 2025

Blood#blood

Blood Type Diet: How Does It Work?

And who said it works?

Dr. Ely28 oct. 2025

Bones and muscles#fitness

What Are the Best Sports That Don’t Harm Our Joints

There is at least one part of our body that does not enjoy sports at all—the joints. What kind of fitness is the best for them?

Dr. Helga28 oct. 2025

Pediatrics#hemoglobin

Blood Transfusion for Premature Babies: A New Perspective

The largest randomized clinical trial on blood transfusion to premature babies was completed by Dr. Haresh Kirpalani of the University of Pennsylvania, Dr. Edward Bell of the University of Iowa, and colleagues from the Neonatal Research Network, including Dr. Rosemary Higgins of the George Mason University College of Health and Human Services. The study was published in the New England Journal of Medicine. To date, this is the most ambitious research in the world that examines blood transfusion in premature babies.

Darya28 oct. 2025

Installez Ornament pour non seulement lire ces articles, mais aussi suivre votre santé, enregistrer vos résultats d'analyses et accéder à d'autres fonctionnalités utiles

Installer Ornament