A hematologist explained why blood should be donated on an empty stomach and in the morning

Diagnostics is a complex process, and one of the most important elements in this chain is laboratory examination methods. The simplest, most accessible and at the same time informative method is a clinical blood test.

Doctor of clinical laboratory diagnostics of the National Medical Research Center of Hematology of the Ministry of Health of Russia, Ph.D., talks about how to properly prepare for the test and other subtleties that are important for the patient to know. Valentina Nikolaevna Dvirnyk.

— Why do blood tests most often need to be taken on an empty stomach and in the morning?

“It’s simple: in accordance with daily biorhythms, the concentration of substances in the blood can vary throughout the day. For example, the indicators of hormones, carbohydrate, fat and protein metabolism, as well as the number of blood cells (leukocytes) change. Blood values ​​taken from the same person may vary at different times of the day. Therefore, the blood values ​​of a healthy person whose blood was taken in the morning are taken as the norm.

Now let’s talk about why blood is usually donated on an empty stomach. The fact is that after eating a whole series of biochemical reactions are triggered in the body. They can distort test results. The concentration of glucose, hormones, and triglycerides of cholesterol are especially sensitive to such reactions.

Therefore, such tests should be taken in the morning and on an empty stomach; moreover, dinner the night before should be light, you should avoid fatty and heavy foods, and drinking alcohol. Fatty foods lead to an increase in the concentration of lipids in the blood, because of this the blood serum becomes cloudy, that is, its optical properties change. The so-called chylosis causes significant deviations in biochemical parameters – indicators of hemostasis. The number of leukocytes increases – these are the cells that are responsible for fighting infections, they are also the main marker of inflammation. Thus, a heavy dinner with fatty foods can distort the test results and complicate diagnosis.

You shouldn’t drink alcoholic drinks either. Alcohol affects basic metabolic processes, including liver metabolism. Under the influence of alcohol, the synthesis of certain proteins, carbohydrates, proteins, lipids, hormones, and vitamins can be disrupted. In addition, the blood thickens.

But we must remember that prolonged fasting can also affect the test result, because energy expenditure decreases, the concentration of glucose, proteins, lipids, and a number of hormones decreases and, conversely, the concentration of bilirubin and cortisol increases.

— Are there blood tests that can still be taken after meals and not in the morning?

— Of course, there are such tests, because food intake and time of day do not affect all indicators. For example, determination of blood type, genetic studies, and tests for infections can be performed at any time of the day and after meals. But nevertheless, it is advisable that the foods you eat are light and low-fat. This is important because fats affect the consistency of the blood and its turbidity, which can affect the test result.

— If a person is not worried about anything and there is no referral from a doctor, is it necessary to squeeze the blood just like that, to check? For example, once a year?

— A blood test is a universal test that can show any abnormalities in health. But if nothing worries you and the doctor has not sent you for a blood test, then you can rely on the recommendations for medical examinations. Any citizen of the Russian Federation can take blood tests during an annual preventive examination – both as part of an independent event and as part of a medical examination. Clinical examination at the age of 18–39 years is carried out once every 3 years, and at the age of 40 years and more – annually. Preventive medical examination and medical examination are carried out within the framework of the program of state guarantees of free medical care. The purpose of such examinations is the prevention and early detection of non-communicable diseases, such as diabetes. If nothing bothers the patient, there is no point in donating blood more often.

— Reference values ​​may differ in different laboratories. Why does this happen and what does it depend on?

— Let’s first understand what reference values ​​are. These are the average values ​​of indicators that were obtained by doctors when examining a large group of healthy people of a certain age and gender.

That is, this is the range of indicators minus the 2.5% lowest values ​​and 2.5% highest values. It is important that the so-called limits of normal laboratory parameters reflect statistical data obtained when taking blood in the morning.

Indeed, they may vary from laboratory to laboratory. This happens because different equipment and reagents are used to perform analyses, and different techniques and units of measurement can be used. Therefore, it is important to pay attention to the units of measurement and reference values; they are always indicated in the analysis form.

— Are there standards for reference values ​​of blood tests?

— There are no such standards. But there are standards for conducting in-laboratory quality control. In the laboratory, before starting work, the condition of the instruments is checked using special samples. If the indicators meet the standards, then the device is ready for use. If not, then measures are taken to bring the devices into compliance.

YOU ARE GOING TO HAVE A BLOOD TEST: A NOTE FOR THE PATIENT

Most tests are taken in the morning and on an empty stomach. The night before, eliminate fried, spicy and fatty foods. Don’t overeat, but don’t starve either.

Avoid alcohol the night before the test.

Those who smoke should stop smoking for a couple of hours before the test.

Strong physical activity is not recommended the day before. It is better to postpone the training to another day.

Try to exclude emotional stress – they can also affect test results. Avoid alcohol and emotional stress and do not exercise on the eve of the test.