Why donate blood on an empty stomach? Is a blood test taken from a vein on an empty stomach or not?

Every person at least once in his life is faced with the need to take blood tests. One of the most common laboratory diagnostic methods is general analysis. It includes several indicators at the same time, which are considered as a whole. Despite its widespread prevalence, many do not know how to properly prepare for a general blood test, whether it should be taken on an empty stomach or not. But the absence preliminary preparation may cause distortion of the results.

A general blood test is one of the most important laboratory diagnostic methods. You can also find the name - general clinical analysis blood. It is used to determine general state body. Despite its simplicity, the analysis is very informative. If any inflammatory processes deviations from the norm will be detected in the body. Its results make it possible to timely determine many serious pathologies, for example, anemia, various infectious and inflammatory diseases.

These are just a few indicators determined by laboratory blood tests. If the doctor suspects a specific pathology, which is characterized by a deviation from the norm of one or another indicator, then it will be required additional research. The results of the analysis may deviate from the norm not only due to illness, but as a result of physical, mental and climatic conditions, as well as if recommendations are not followed before taking the test.

Preparing for analysis

The procedure for carrying out a general analysis is simple. For research, a fence is taken capillary blood from a finger. To ensure that the results are not distorted, it is necessary to carry out simple and completely doable preparation. Before donating blood you need to:

Follow a non-strict diet. You should avoid spicy and fatty foods for 2-3 days before the test. Drinking alcoholic beverages is strictly prohibited.
Take a blood test on an empty stomach. Food increases the level of leukocytes, which is why it is forbidden to eat before the test. You can take the test 8-10 hours after eating, that is, after a night's sleep. You should also not have breakfast before going to the laboratory. You can drink drinking water; it does not affect blood counts.
Be sure to quit smoking before the test.
Eliminate any loads. You may get distorted research results after severe stress, physical fatigue. Before entering the office and donating blood, it is recommended to rest for a few minutes; you can drink water, as it helps you calm down faster.
Do not perform X-ray examinations or physiotherapeutic procedures in the previous 10-12 hours.

If treatment with medications has already been prescribed and it is not possible to stop taking them, then you must inform your doctor about this. Most medications change the value of some indicators, which is why it is possible that the diagnosis will be incorrect. It is better to temporarily stop taking medications a few days before the test.

The ideal time to donate blood is between 7-12 hours. This is primarily due to the fact that after lunch and throughout the day, many indicators change. Also during this period the person does not yet experience strong feeling hunger after an evening meal, which does not affect emotional condition. If blood is donated at a later time, then most likely the patient has already had breakfast, and as already noted, blood must be donated on an empty stomach. You can’t eat, you can only drink water, otherwise there is no chance that the results will be reliable.

Why do you need to take the test on an empty stomach?

Many people are interested in the question: why is it necessary to take a blood test on an empty stomach? Is it possible or not to drink water? You can hear and read a lot of advice on this matter. Some claim that they always donate blood after meals and all indicators are normal. But there is one correct answer to this question - blood must be donated on an empty stomach. In connection with why this need arises, let us consider in more detail.

The doctor prescribes a test to assess the state of health or if there is already a suspicion of an inflammatory process or infection of the body. It is the result of the blood test that will confirm or rule out the development of the disease. If the value of the indicators deviates from the norm as a result of non-compliance with recommendations (including blood donation not on an empty stomach), then there is a possibility that the diagnosis will be made incorrectly. Accordingly, the treatment will be incorrect, and perhaps completely unnecessary.

After meals nutrients are absorbed into the blood and affect its composition, including the concentration of proteins, fats and other compounds, change viscosity, and increase the level of indicators, one of which is leukocytes. So, if blood is not donated on an empty stomach, then most likely the level of leukocytes will increase significantly. And its increase indicates the presence of an inflammatory process or infection in the body.

If the patient has a history of other health complaints, the doctor will most likely prescribe an additional examination and appointment. medicines.

Additional diagnostic methods require a certain amount of time, and while their results are not yet available, the patient will take medications. As a result, it may turn out that the patient has no pathologies, and the test results were distorted due to the fact that the blood was not donated on an empty stomach. Therefore, no medication was required. And as you know, the use of medications is extremely undesirable without indications, since they can cause harm to the body. In addition, time and money spent on additional examination will be wasted.

There is an exception to the rules when taking a blood test - these are patients with diabetes mellitus or pancreatitis. For this category of patients, long breaks between meals are unacceptable. Patients with diabetes and pancreatitis are allowed to have breakfast before the test. But there are certain requirements for food. Breakfast should be light. You can eat porridge with water without sugar and butter, a sandwich with cheese, dried bread or some fresh vegetables. You can also drink weak tea without sugar, but it is better to limit yourself to water.

General blood test is common and informative method diagnostics Preparing for research does not require complex restrictions. You just need to comply simple recommendations. The main requirement is that blood must be donated on an empty stomach, but pure blood is allowed. drinking water. If preparation for the analysis is carried out, the results will be reliable, and the doctor will not be misled and will not prescribe unnecessary treatment.

One of the very first diagnostic methods, which is prescribed to all patients, is blood donation. During the study, experts evaluate dozens of indicators, because blood can tell doctors about the presence of hidden diseases, a possible relapse of the disease, and the effectiveness of the prescribed treatment. Before the analysis, the doctor must explain to each patient how to donate blood from a vein on an empty stomach or not, what other rules need to be followed and why this is so important.

Deoxygenated blood

A blood test from a vein is an informative test that can tell a lot about the patient’s health status. Venous blood is used to determine the most important parameters.

Tests that require venous blood can be divided into several types, namely:

Analysis of general indicators.
Analysis of biochemical composition.
Glucose level test.
Serological study.
Test for hormone levels.
Analysis for tumor markers.
Test for determining the Rh factor, etc.

All these tests must be taken strictly on an empty stomach in the morning. Why is blood donated on an empty stomach, and what other rules for donating blood are important to follow? How can food intake affect test results and is it possible to smoke before taking blood?

Why can't you eat

Blood from a vein on an empty stomach or not? Today you can often find information that this requirement before taking a blood test is already outdated. Some laboratories claim that modern equipment makes it possible to study the biomaterial of a person who ate food earlier than 8 hours before analysis. However, experts still advise patients to strictly follow this rule, but why?

The thing is that every meal distorts the composition of the blood. When we eat, we receive a lot of nutrients that go directly from the intestines into the blood. The biochemical composition of the blood changes at this moment and if you consumed food, the results may be inaccurate. How can food affect a particular analysis?

Biochemistry. Biochemical analysis is a study of blood composition according to 11 main criteria. It allows you to identify many diseases at the earliest stages of development. The study helps determine diseases of the liver, kidneys, heart, stomach, blood vessels and others important organs and systems. For this reason, blood for testing should not contain excess fat, sugar, microelements, etc. So, for example, you eat dried fruits before donating blood, they are rich in potassium, doctors will detect an increased content of this element and diagnose you renal failure, also with other components of any food. After eating, glucose, cholesterol, hemoglobin, etc. may increase. The result is an erroneous diagnosis and incorrect treatment.

What else is not allowed

Many patients are interested in whether it is possible to smoke before donating blood, the answer is categorically no! Smoking causes the destruction of blood cells, oxygen starvation and impaired blood flow. If you smoke before the test, your readings will be significantly distorted and doctors may suspect that you have dangerous diseases. In addition to smoking, you should definitely avoid alcohol and even chewing gum.

In addition to restrictions on eating and smoking, there are several more rules that must be followed before taking the test. venous blood. First of all, this applies to taking any medications. If you are prescribed a blood test, you need to stop taking medications 3-5 days in advance.

If you do this by various reasons If it fails, you must inform your doctor about this.

It is also necessary to reduce physical activity to a minimum several days before blood sampling. During intense exercise, protein breakdown occurs in the muscles, and some levels of residual nitrogen increase sharply. These substances are often used to diagnose kidney disease.

What can you drink

Is it possible to drink water before donating blood from a vein? This is another question that worries many patients. Yes, you can drink, but it should only be ordinary boiled water. It is not recommended to drink mineral or carbonated water. The composition of such water may also influence the results of the study.

However, you need to drink a little. Water does not affect the composition of the blood, but for some people drinking large quantity Liquids on an empty stomach are prohibited. For example, in patients with hypertension, this can cause increased blood pressure. Such patients can drink a few sips of water. Sugary drinks are not allowed.

When can you eat

There are a number of tests before which eating is not prohibited. You can eat before genetic research blood. Human DNA cannot be affected by food.

For this reason, paternity tests, tests for genetic diseases, nationality determination and other DNA tests can be taken without special preparation.

Sometimes in extreme cases, for example, during emergency hospitalization, the patient’s blood is taken for testing, regardless of whether he has eaten or not. In this case, doctors take into account the urgency of the analysis and take into account only serious deviations in parameters that cannot be caused by food intake.

Anyone scheduled for a blood test is advised to bring food with them. For example, you can take chocolate bar or a bun and eat them after the blood draw, especially if after this you still need to go through additional medical procedures or visit a doctor. Also today in almost all medical institutions There is a buffet where you can have a snack after the analysis.

In contact with

Almost all studies are carried out on an empty stomach (at least 8 hours after last appointment food), so you can drink a small amount of water to carry out tests in the morning. Tea and coffee are not water, please be patient. Taking tests requires quitting smoking an hour before the procedure.
Strictly on an empty stomach, more than 12 hours after the last meal: general blood test, biochemical parameters(cholesterol, HDL, LDL, VLDL, triglycerides).
After 5-6 hours of fasting (the last meal should be light, without high content fats) you can take tests: for hormones (in the morning), antibodies to infections (during the day). Please note that a blood test for antibodies to infections reflects the state of immunity in relation to infection. If the infection is recent, the results may be negative. In doubtful cases, it is recommended to retake the test after 7-10 days (for toxoplasma, rubella and cytomegalovirus during pregnancy- confirmatory immunoblot study).

Analyzes throughout the day

Regardless of meal(not necessarily on an empty stomach): genetic polymorphisms, including polymorphisms of hemostasis genes, vascular tone, polymorphism of cytokine genes, AZF factor, mutations of CYP-21, PCOS, CFTR gene, HLA typing.
After 3-4 hours of fasting you can take tests for hCG, antibodies to infections in the blood, tests for HIV, syphilis, hepatitis B and C, blood type, Rh factor, antibodies to Rh factor, anti-group antibodies, autoantibodies (from the autoantibody panel), prenatal screening, tumor markers .
During the days and hours of operation of the Center tests are taken for PCR diagnosis of infections, culture of vaginal discharge (including culture for mycoplasma and ureaplasma), microscopy of a smear from the vagina and cervix, microscopy of a smear from the pharynx, PAP smear, donation of mucus for the Kurzrock-Miller test.
Laboratory standards are calculated for morning indicators. Tests for TSH, parathyroid hormone, and iron are taken only before 11 a.m.(the value of the indicators changes significantly during the day).
The day before the test, avoid stress, physical activity, changing the daily routine and changes in diet, drinking alcohol.
It is advisable that the tests be taken in a calm state. Therefore, if on the way to treatment room If you were in a hurry or worried, it is recommended to sit for 20-30 minutes before donating blood. Attention! Before taking some tests ( ACTH, cortisol, growth hormone or growth hormone) you need to completely calm down and relax. Please sit in the waiting room for 30-40 minutes.
A PSA test is carried out no earlier than 7 days after any mechanical effects on the prostate (massage, biopsy, etc.)
Studies are carried out without taking medications or 11-14 days after their discontinuation (except in cases where this is allowed by the doctor). In the questionnaire, be sure to indicate the names and regimen of medications taken.
Some tests need to be taken only on those days when prescribed by a doctor (for example, hormones of the female reproductive system, EFORT test, on certain days of the cycle; some - according to the stage of pregnancy). Please indicate in the form the day of your cycle and the duration of your pregnancy.
Repeated studies are best performed in the same laboratory, since they are used in different various methods research, norms of indicators.

Attention! There are procedures with special training and method of material collection.

Modern medicine cannot be imagined without blood tests. They are necessary to correctly diagnose and prescribe treatment. According to the World Health Organization, laboratory diagnostics provides up to 80% of information about the state of health of the human body. The reliability and accuracy of test results depends both on the technical level of equipment of the laboratory, the professionalism of the laboratory doctor, correct fence blood average medical personnel, and from the patient’s compliance with the prescribed rules for preparing for blood donation.

Getting ready to take tests

To test blood biochemically or to determine hormone levels, it is necessary to take at least 2 ml of blood from the patient. This amount of test material can only be collected from a vein. And if blood is collected correctly, then already at this stage the likelihood of damage to the integrity of blood cells is significantly reduced. And this, in turn, affects the final test results.

The main condition is to donate blood on an empty stomach.

Almost all blood tests are taken strictly on an empty stomach. For example, biochemical studies are performed on blood glucose, lipid spectrum, urea, creatinine, bilirubin, hormones and others. In order to take fasting blood tests, the last meal before the blood draw must take place eight hours before the procedure. And to take a blood test for lipid spectrum(cholesterol, triglycerides, high and low density lipoprotein cholesterol) - eating at least twelve hours before.

Is it possible to drink juice, tea, coffee before taking the test?

Unfortunately, you cannot drink juice, tea, or coffee; these drinks affect blood counts and consuming these drinks is not recommended. However, you can drink plain water. It is also necessary to exclude fatty, fried foods and alcohol from the diet two to three days before the examination. If there was a festive feast the day before, it is advisable to postpone the laboratory test for one or two days, and an hour before taking blood, refrain from smoking.

To determine the true level of blood lipids, it is necessary to exclude the consumption of animal fats, caviar, cheese, sausage, and egg yolk a week before the test. If this is not done, lipid levels will be elevated due to the intake of these ingredients in food.

Detailed or general blood test

If you have to take a detailed or general blood test (finger prick), then the last meal should be 1 hour before the procedure and may consist of unsweetened tea, unsweetened porridge without milk, butter and an apple.

Blood for infectious diseases

Some blood tests are not required strict restrictions. Donate blood to check for antibodies to HIV, viral hepatitis, rubella, cytomegalovirus and others infectious diseases You can do it in the morning, afternoon or evening without prior fasting. Since the patient has already been infected, the concentration of antibodies to the infection in his blood remains stable at any time of the day, as well as before, during or after meals.

Hormone tests

The content of hormones in the blood is subject to daily (circadian) fluctuations, so blood to determine TSH, parathyroid hormone, and iron is taken on an empty stomach strictly before 11 a.m., and blood cortisol is determined at 8.00 and 20.00. It is necessary to always study hormone levels at the same time. In this case, the dynamics of the results obtained will be more correct. For correct definition TSH level in the dynamics of treatment of hypothyroidism, blood must be donated before taking replacement therapy.

Blood is given for analysis before the start of the appointment medicines (for example, antibiotics and chemotherapy drugs) or no earlier than 10-14 days after their discontinuation. Be sure to notify your doctor if you are taking medications.

Before drawing blood, you need to rest for 10-15 minutes in the waiting room and calm down. If you've been nervous, this can cause your blood sugar to rise.

When examining for the presence of infections, it should be taken into account that, depending on the period of infection and the condition immune system any patient can have negative result tests, but it does not completely rule out infection. In doubtful cases, it is recommended to re-examine after some time, but not earlier than three to four weeks.
During hormonal studies in women reproductive age(from about 12-13 years of age until menopause) influence the results physiological factors related to stage menstrual cycle . Therefore, to determine the level of FSH and LH, they are taken on the fifth to seventh day of the menstrual cycle. To determine the level of estradiol and progesterone - on days 21-23.
To reduce the likelihood of hematoma (bruise) formation at the site of vein puncture after blood collection, it is necessary bend your arm at the elbow and hold for 15 minutes. In the evening, make a compress with a semi-alcohol solution for 15-20 minutes.
If, when drawing blood for laboratory research you are experiencing fear, dizziness, weakness, are afraid of losing consciousness - warn the procedural nurse in advance, and your blood will be taken in a lying position.
Many laboratories can conduct an anonymous examination, but if you need official result, take your passport with you.
Anonymous results are not accepted during hospitalization, at the OVIR, embassies and some other places.

Remember that systematic tests can provide an accurate picture of your health status. Until the age of 30-40, they should be taken annually, and after 40, once every six months. In the presence of chronic diseases The regularity of examinations may be more frequent - once every three months or even monthly.

A set of regular laboratory tests allows you to obtain a timely and reliable assessment of your health status. The comprehensive examination includes the following laboratory indicators. Biochemical blood test (11 main indicators) characterizes the state of liver, kidney, carbohydrate, protein and fat metabolism. General blood and urine tests, determination of C-reactive protein. These tests will show the presence or absence of inflammatory processes in the body. Analysis for the presence of viral heptitis (HCV, HBsAg).

If there is a deviation from normal values at least one of the indicators, you should consult your doctor.

Remember that you need to consult a doctor in time to draw up an examination plan in accordance with your complaints, objective examination data, concomitant pathology, and he will help you explain the test results.

Blood tests are a common method of examination. It allows you to identify malfunctions individual organs, identify certain diseases and find out the cause of symptoms. Before you put serious diagnosis and prescribe treatment, doctors compare test results with the patient’s health condition.

Usually, before undergoing tests, the patient is warned that the procedure is to be carried out on an empty stomach. Neglecting this rule, analysis can show incorrect results, and the doctor will prescribe inappropriate treatment based on them.

As confirmed by multiple studies, eating before taking the test can indeed distort its results. In some cases, food completely makes it impossible to perform the procedure. This is due to the fact that nutrients that are absorbed into the blood affect the concentration of fats, proteins and other compounds in it. Food can also activate enzyme systems and change blood viscosity. Nutrients also increase hormonal levels, which affects the condition of the blood being tested.

As you can see, the blood test procedure is very important and you need to prepare for it, that is, not eat for a certain time. The duration of fasting before donating blood depends on the type of analysis.

Blood donation depending on meal times:

General clinical (general blood test) - taken from a finger, determines the level of hemoglobin, ESR, number of red blood cells, platelets and leukocytes, leukogram results. 8 hours should pass after the last meal.
Biochemical - taken from a vein, determines carbohydrates, lipids, proteins, vitamins, nitrogen compounds. The interval from the last meal should be at least 12 hours.
Blood sugar level - taken from a finger prick, last meal 8-12 hours before the test.
Serological (for hepatitis, syphilis, HIV) - analysis is carried out after 8 hours from the last meal.
Tests for hormones - on an empty stomach, 5-6 hours should pass since the last meal.
Analysis for Rh factor - food intake does not depend on the result.
Analysis for tumor markers - you will have to abstain from food for 3-8 hours.

You don't need to make any big sacrifices to take a blood test. To avoid having to fast on purpose, just eat in the evening and head to the clinic in the morning. Do not neglect the recommended rules for donating blood, because your health depends on the result!