Why tests should be taken on an empty stomach

Health Tips

Incorrect preparation for the delivery of the analysis leads to an error in assessing your condition.

What does “on an empty stomach” mean

This means that before donating blood, you cannot eat for a certain period of time (usually 8-12 hours). But even if it is said about some analysis that “on an empty stomach is not necessary”, 4 hours of complete abstinence from food are still assumed. It’s not even that some significant indicators will change against the background of satiety. Blood type, HIV (as well as other viruses) or tumor markers will remain with you regardless of whether you ate or not. But if you ate (especially fatty foods), the quality of the obtained blood sample deteriorates – it is more difficult to “bind” the desired analyte. In addition, after eating, the transparency of the serum worsens, and this can lead to an error in the measurement.

But you can drink a glass of water (200 ml) before donating blood – this will not “dilute” the blood. The volume of human circulating blood is approximately equal to 5 liters (about 70 ml per 1 kg of weight). Drinking water will not have time to absorb everything into the blood and significantly affect its composition. In addition, the volume of circulating fluid is clearly regulated by healthy kidneys – if you drink a lot, then urine will be excreted accordingly.

What does food affect

Diet affects the results of most indicators

blood: both direct – due to the absorption of food components and an increase in the concentration of the studied parameters, and indirect – for example, the level of hormones changes immediately after eating. Even if you donate blood on an empty stomach (for example, in the morning), then your last meal (dinner) should not be fatty: a high concentration of fat in the blood can interfere with any study.

The concept of “fasting” also implies the rejection of tea and coffee, juice and carbonated drinks, sugar or honey. All of the above includes various chemical components that can significantly distort the results of the analysis. Here are the (minimum!) Errors that can appear in the results if you had dinner too tight or too late or drank not water, but tea or coffee in the morning:

  • General clinical blood test – an increase in the number of leukocytes in the blood.
  • Blood chemistry – incorrect value of the level of carbohydrates, lipids, proteins, nitrogenous compounds. Moreover, too long (more than 14 hours of fasting) also leads to a distortion of the expected result: the indicators of some blood lipids can significantly decrease.

What, besides food, affects the result

Before donating blood, you can not only eat, but also take medication, smoke, overexert.

  • Any medication affect the body. It is recommended to stop taking medications at least a day before the test, after agreeing this with your doctor. If it is not possible to stop taking medication, this should be reported at the time of blood donation and to your doctor, who will evaluate the result taking into account “background factors”.
  • Alcohol and smoking significantly affect metabolic processes, this can lead to changes in the concentration of most biochemical blood parameters. For example, drinking alcohol lowers blood sugar and raises cholesterol, while smokers increase levels of the stress hormones catecholamines and cortisol. Before the study, it is necessary to stop drinking alcohol at least a day in advance, smoking – 30 minutes in advance.
  • Serious physical activity (for example, in the gym) on the eve of testing is also contraindicated: they lead to a noticeable change in hormone levels and can affect blood glucose levels.

All this, of course, does not apply to emergency situations. Upon admission to the hospital by “Ambulance”, the necessary tests can be performed at the direction of the doctor at any time of the day, without regard to food intake.

Photo: www.istockphoto.com

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