Introduction
Blood testing is a frequently used method, both in the clinic and in medical practices. It provides information about the function of our organs, about enzymes that are important for our metabolism, about the coagulation of our blood and much more. Various parameters are then examined in the blood.
Each of these parameters can provide information about a possible disease. In diabetics, for example, daily blood monitoring is important to keep the blood sugar level constant. Even a tiny drop of blood can tell a diabetic how much insulin he or she needs.
Thus, the blood test also serves to monitor health. Depending on what is examined, the patient should be fasting, which means that he or she should not have drunk or eaten anything. This is especially important when examining the blood sugar level.
Diagnosis/procedure
In order to be able to make a diagnosis, venous blood is first taken from the patient using a cannula or a so-called butterflies. The most common place for taking blood is the bend of the elbow, since a vein (Vena mediana cubiti) lies very superficially here and is therefore easy to find for most patients. The patient is fitted with a cuff on the upper arm for the collection, which is then closed.
This allows the blood to accumulate in the vein and the vein to emerge even better. Depending on the blood test, 2 ml of venous blood is usually sufficient. Many parameters can be tested using one sample, but for some tests it is advisable to take several blood samples to achieve better accuracy.
In some patients, the vein in the elbow area may not be clearly visible and may be difficult to locate. In this case, it is advisable to take blood either from a hand vein or from a foot vein, as these are also more superficial. In general, it is possible to draw blood from any superficial vein.
The blood taken is always whole blood, which means that the blood still contains all substances such as coagulation factors. This whole blood can be used, for example, to determine the pH value of the blood or the blood sugar concentration. A distinction must be made between whole blood and blood plasma and blood serum, which play a decisive role in blood donation.
To obtain blood plasma, EDTA (ethylenediaminetetraacetic acid), sodium citrate or heparin must be added to the whole blood. These prevent the blood from clotting. By centrifuging the whole blood, you will obtain blood plasma.
This blood plasma consists of the non-cellular part of the whole blood. 90% is water. The remaining 10% contains electrolytes (sodium, potassium …), hormones, proteins, nutrients and breakdown products.
In order to obtain blood serum, the clotting process is allowed to take place. In the process, a solid, clumped part, the blood thrombus, and a yellow, clear liquid is formed. This yellow liquid is the blood serum and corresponds in its composition to plasma, but no longer contains fibrinogen (a protein complex which ensures that the wound is primarily sealed with a kind of blood crust during wound healing).
The blood test is therefore always an examination of the whole blood, which still contains all the components. A distinction is made between different procedures for the blood test. Very important for the diagnosis of a disease, is the creation of a so-called blood count. Here one differentiates between 2 forms: The so-called small blood count and the differential blood count. Both together are called the large blood count.
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