What is hematocrit?
The hematocrit (abbreviation: Hkt, Hct or Hk value) is a laboratory value that is determined from the blood count after a blood sample is taken. Human blood consists of cells and liquid components that are in a certain ratio to each other in healthy people. By definition, the hematocrit indicates the percentage of cells in the blood . It can be calculated by dividing the cellular volume by the total blood volume.
This cellular part of the blood in turn consists of three cell types:
- 99 percent make up the red blood cells, the erythrocytes. They serve to transport oxygen.
- There are also white blood cells (leukocytes), which are part of the immune system.
- The third type of cells are the platelets (thrombocytes), which play a major role in stopping bleeding.
In addition to this cellular part, the blood consists of a liquid part. This is called blood plasma . If one looks at the blood plasma without the so-called coagulation factors, i.e. certain proteins , one speaks of blood serum.
What does the hematocrit say?
A shift in the hematocrit outside the normal range indicates an imbalance in the blood components. Both the cellular components and the blood plasma can be altered in terms of quantity and volume. As a result, the blood becomes either too viscous or too liquid, and the hematocrit is then correspondingly too high or too low.
Possible causes for this are, for example, anaemia , in which fewer red blood cells are formed, overproduction of blood cells in the bone marrow, loss of fluid and thus also of blood plasma or excessive administration of fluid, which then affects the plasma volume.
When and how is the hematocrit determined?
The hematocrit is part of the small blood count, so it is routinely determined during a blood test , for example as part of a check-up. But the blood value is also determined if various diseases are suspected, for example in the case of dehydration , for example due to gastrointestinal infections, internal bleeding and hematological diseases such as anemia.
The blood sample is taken from the vein. To determine the hematocrit value, the blood sample is then either spun in a centrifuge, which separates the blood components and allows them to be measured. Or the determination is made using a blood cell counter. The Hkt value is given as a percentage.
A change in the hematocrit is almost always caused by the erythrocytes. Additional laboratory tests, such as hemoglobin and erythropoietin levels or a bone marrow test, may be needed to determine the cause of the change.
Standard values - how high can the hematocrit value be?
The normal values for the hematocrit differ according to gender and age. We have compiled the normal values for you in the following table:
It should be noted that normal hematocrit values may differ slightly depending on the laboratory. The stated values are therefore only approximate.
What does a high hematocrit mean?
If the hematocrit value is too high, there are more blood cells and less blood plasma in the blood. As a result, the blood becomes more viscous and its flow behavior in the blood vessels changes. As a result, there is a higher risk of blood clots ( thrombosis ) forming. These lead to vascular narrowing and occlusion and can cause, among other things, poor blood circulation in the extremities, strokes and heart attacks . A hematocrit that is too high can therefore be quite dangerous.
The signs of an elevated hematocrit depend on the cause. If the values are slightly elevated, symptoms rarely appear. If the values are significantly higher, however, complications such as the thrombosis mentioned above can occur.
Symptoms that may indicate an elevated hematocrit include:
Causes of increased hematocrit
If the hematocrit is too high, this can have two meanings:
- There are too many blood cells in the blood.
- There is not enough fluid in the blood.
Causes of too many blood cells in the blood
The blood cells are formed in the bone marrow. Normally, the production and breakdown of blood cells are in balance. In certain diseases, however, there is an overproduction of blood cells.
If only the red blood cells are formed too much, this is called polycythemia. The red blood cells are responsible for transporting oxygen. If their number is increased, the body tries to compensate for a lack of oxygen. This can be caused by lung and heart diseases. The messenger substance that stimulates the formation of erythrocytes is called erythropoietin (EPO) and is formed in the kidneys. Polygobulia can also indicate a change in the metabolism of this substance, for example due to a kidney tumor or the administration of additional EPO for medical reasons or as doping.
If all blood cells are produced in excess, it can be a so-called polycythemia vera. Due to gene mutations, the blood cells begin to multiply independently. Regulation by the body is no longer possible. Those affected often suffer from itching , which occurs particularly after contact with water, and are prone to bleeding from the nose and gums.
Causes of insufficient fluid in the blood
The amount of blood plasma decreases when a person dries out (desiccates), also known as dehydration. This can be caused, for example, by excessive sweating during physical exertion or not drinking enough water.
Lower the hematocrit
In order to be able to lower the hematocrit, the cause must first be found. If the only reason is a lack of fluids, you can naturally lower the hematocrit by drinking a lot. If necessary, the doctor will give infusions to thin the blood more quickly. Here, too, it must be clarified that there are no pathological causes for the lack of fluids.
In the case of polycythemia, regular bloodletting helps to reduce the cell count, since the body reproduces blood plasma faster than blood cells. In addition, those affected are given medication such as acetylsalicylic acid (ASA), which has a blood-thinning effect and thus counteracts thrombosis.
What does a low hematocrit mean?
If the hematocrit value is too low, the plasma volume is proportionally increased and the cell count reduced. The most common cause of a low hematocrit is anemia. When you have anemia, you have either too little hemoglobin (also known as red blood pigment) and/or too few red blood cells. The hemoglobin, which is contained in a certain amount in the erythrocytes, ensures the transport of oxygen in the human body. If less hemoglobin is available, less oxygen can be transported.
Anemia is manifested by the following symptoms:
In order to treat anemia, its cause must be found. Iron deficiency is often the reason and can easily be compensated for with iron tablets. But some cancers, vitamin deficiencies and chronic bleeding can also lead to anemia, for example. A visit to the doctor helps to find the right therapy.
Another reason for a low hematocrit is too much fluid in the blood. This occurs most frequently after the administration of infusions. An infusion supplies the body with liquid via the vein, but not the cellular components of the blood. The body first has to replicate this itself, which takes some time. In addition, a lower hematocrit value is normal during pregnancy. Endurance athletes also often have low hct values, since the plasma volume is increased more than the cell count to adapt to the physical exertion.
