Blood carries oxygen from the lungs to the organs, and on the way back it takes back the waste product carbon dioxide for exhalation. It is also the main artery for the numerous other substances that need to get from one place to another in the body. All the substances that travel in the blood can be measured. Blood tests are an important part of most medical examinations.
Blood – body fluid with numerous tasks
Most substances in the body need to get from one place to another. Whether it’s nutrients in the gastrointestinal tract to other organs, oxygen in the lungs to body cells, hormones from endocrine glands to their target cells – the number of substances transported back and forth in the bloodstream every day is huge. But blood also has other tasks: For example, it distributes heat and is part of the regulatory system that ensures that the optimal internal environment is maintained in the body (homeostasis). The coagulation system seals injuries. A very important function is also the immune defense, in which defense cells and antibodies are provided in the blood and fight pathogens, foreign proteins or diseased cells in the body. Understanding laboratory values: A check of the most important abbreviations
Components of blood
In adults, blood makes up about 8 percent of body weight, or about 5 to 6 liters.
- 42 to 44 percent of the blood volume is due to the blood cells – experts refer to this proportion as hematocrit.
- The remaining 56 to 58 percent is the blood plasma or plasma volume. This consists of 90 percent water, 8 percent proteins and 2 percent small-molecule substances such as vitamins, sugars or hormones.
Blood plasma without fibrinogen, a protein body of blood clotting, is called blood serum.
What is examined and for what?
A variety of different tests can be performed on a single blood sample, depending on which component of the blood is being looked at and how. For example, primarily whole blood, blood cells, and blood serum are examined. However, each examination is always only a snapshot and may have to be repeated. There are also some factors that influence the result and therefore must be taken into account during the evaluation. These include:
- Age
- Gender
- Diet
- Time of day
- Medication
The standard values used for comparison may vary from laboratory to laboratory and depending on the method of examination.
What blood tests are available?
In principle, the following tests can be distinguished:
- Blood count
- Blood clotting
- Blood cell sedimentation rate
- Examinations of the blood serum (serological examinations).
- Blood gas analysis (BGA)
- Blood culture
- Blood smear
Only the synopsis of the most diverse parameters gives the doctor an indication of the possible disorder. Depending on the suspected disease and cause, the blood tests are often supplemented by other diagnostics such as function tests and imaging techniques such as ultrasound öder X-ray. Blood tests are also well suited for monitoring the course of diseases and treatments. For example, deterioration of organ function, adjustment and side effects of medication or the flare-up of a tumor can be detected at an early stage. We present the individual blood tests below.
1. small and large blood count
Microscopically and photometrically, blood cells (red blood cells, white blood cells, platelets, immature red blood cells) and blood pigment are looked at, as well as their appearance, number, size and percentage distribution. Depending on which blood cells are examined, a distinction is made between small and large blood counts. This examination is used especially in cases of suspected infections, blood diseases such as anemia or disorders of blood formation and deficiency diseases (for example, iron, folic acid, vitamin B12).
2. blood coagulation
The coagulation system protects the body from bleeding and blood loss. There is a complex balance between stopping bleeding from clots on the one hand and keeping blood fluid so that vessels do not become clogged on the other.A number of different factors are involved in this; the most important are the blood platelets (thrombocytes), fibrinogen, calcium and vitamin K.
Blood coagulation testing is performed primarily in cases of suspected congenital or acquired coagulation disorders and certain organ diseases (for example, liver).
3. blood cell sedimentation rate
This is a survey test in which unclotted blood is drawn into special tubes and the distance by which the solid components sink in a given period of time is determined. If this is larger than normal, it may indicate infection, inflammation and tumors; if it is smaller, it may indicate liver inflammation. Further investigations must follow.
4. blood serum studies.
Serological examinations are used primarily to assess the function of internal organs such as the liver and gallbladder, kidneys, heart, lungs, stomach and intestines, thyroid, pancreas, spleen, and prostate. Proteins, fats, minerals, vitamins, hormones, enzymes and cancer markers can be determined – important examinations in identifying a wide variety of disorders and deficiencies and in monitoring the course of disease and therapy. Certain enzymes are typical for the functional diagnostics of various organs and are also named accordingly (for example, heart, liver, muscle enzymes). These are groups of substances whose concentration and percentage distribution usually give the physician important information about the type of functional disorder of the specific organ. They are usually assessed in combination with other substances such as protein or fat.
5. blood gas analysis (ABG).
Blood gas values include the concentration of oxygen and carbon dioxide, as well as pH and bicarbonate. The blood sample is usually taken from the artery in the wrist or the capillaries in the ear. This can be used to assess gas exchange in the lungs, for example in diseases such as asthma.
6. blood culture
This microbiological procedure involves incubating blood in an incubator to detect bacteria and then determine the appropriate antibiotic for therapy. It is used, for example, in cases of high fever of unexplained cause.
7. blood smear
Here, fresh capillary blood is smear on a glass slide and evaluated under a microscope. It may be stained and is used to examine for parasites (for example, malaria pathogens) and to view and count blood cells.
Obtaining a blood sample
Depending on the intended test, one or more tubes of blood are drawn; the amount is usually 2 to 50 milliliters. In most cases, the blood is drawn from the vein (for example, in the crook of the arm), or from the artery or capillaries for specific questions. Some tests require certain preparation on the part of the patient – it is not uncommon for the patient to be fasting, for example when blood lipids or blood sugar are being determined. The physician will inform the patient about the necessary measures and preparations in each individual case. A variety of different tubes are available for storing and transporting blood samples. For example, the blood used to determine coagulation must be prepared differently from the blood used for sedimentation. Today, the tubes are already supplied by the manufacturer ready for use with the appropriate additives, usually recognizable by different colored stoppers. The collection systems are designed in such a way that they only have to be pierced once and yet several tubes can be filled. In some cases, the physician also takes only one large syringe and then fills it into different containers. When taking blood for a culture, the physician must take special care to work sterilely. Otherwise, if the sample is contaminated, such as with normal skin germs, it may not be evaluated properly.
