Blood collection

What is a blood draw?

When taking a blood sample, a doctor draws blood from the vascular system for examination.

Blood collection is always carried out under sterile (aseptic) conditions so that the risk of infection at the injection site is as low as possible.

When do you take a blood sample?

In addition to donating blood, blood is collected primarily to obtain information. Based on blood counts, doctors can draw conclusions about illnesses or deficiencies based on the composition. Blood consists of red blood cells (erythrocytes), white blood cells (granulocytes), platelets (thrombocytes), coagulants, and blood serum with proteins, electrolytes, nutrients, and hormones. For example, an increase in so-called C-reactive protein indicates an infection. In addition, an arterial blood sample can be taken as part of the gas analysis.

How does a blood sample take place?

The most common type is venous blood collection from the crook of the elbow. The cuff, the so-called tourniquet, is placed on the arm and tightened so that, on the one hand, blood can collect in the veins and, on the other hand, you can still feel the arterial pulse.

The doctor palpates the best injection site and disinfects it thoroughly. Now the vein is punctured with a needle or with the so-called butterfly system, in which the needle is also passed through two wings. The puncture through the skin may cause mild, short-term pain. Blood collection tubes are attached to the tip of the needle and a vacuum is generated by means of a stamp, which accelerates blood collection.

When the tube is filled enough, it is removed from the needle, the plunger is bent and the tube is tilted a few times. This causes the blood to combine with anticoagulants or other reagents that are already in the tubes and not clump. The most common is EDTA blood, in which the blood components remain unbound due to ethylene diamine tetraacetate (EDTA) contained in the tube. This is the only way to examine the cells in the laboratory.

Finally, the doctor opens the congestion tube, pulls the needle and presses the puncture site with a compress so that there is no bruise. A patch protects against infections.

Do I have to show up on an empty stomach for a blood test?

It is important to draw blood while fasting so that your blood levels are affected as little as possible. What does fasting mean for blood collection? In principle, this means that you shouldn't eat anything eight to twelve hours before. This makes it easier to compare your blood values, as food primarily influences blood sugar and blood lipid levels. The enzyme balance also changes as soon as the organs start digesting.