Hematocrit

Hematocrit (abbreviation: Hct, Hct or Hk ) denotes the fraction of erythrocytes on volume of blood. Since erythrocytes physiologically represent 99% of the total volume of the blood cells, hematocrit value corresponds approximately to the proportion of the cell volume on blood volume. In addition, the hematocrit value can provide information on the water balance of the patient.

The hematocrit is determined by centrifuging a coagulation- free blood sample in a test tube. The clotting of blood is thereby prevented by the addition of EDTA (ethylenediamine ) or heparin. The heavier red blood cells settle to the plasma, the amount of red cell column is measured in relation to total blood column. The boundaries between erythrocytes, leukocytes / platelets and blood plasma are visible to the naked eye.

Normal values

Normal hematocrit values ​​are in men 42-50 % in women and 37-45 %. Even after a strong blood flow to the hematocrit may be normal, since both cells and fluid are lost.

In other vertebrates, the hematocrit between 20 and 65 % may be.

The optimal hematocrit is on the model calculations of flow physics point of view ( the viscosity of a liquid depends on the viscosity of the solvent and the volume fraction of its solid constituents from ) at about 40%. The normal hematocrit of humans and many animal species so appears to be optimal from this viewpoint.

In deviation of the hematocrit value of the " normal values ​​" can also be the measure of the blood glucose measurement differ.

Increased hematocrit

A high hematocrit indicates a high erythrocyte fraction ( polycythemia ) or a lack of fluid (see dehydration and dehydration ).

Maximum values ​​at high altitudes (eg in high altitude mountaineering ) arise and go up to about 70 % hematocrit by long stays. The viscosity of the blood is kept here in a natural way by a corresponding increase of anticoagulant enzymes remained within acceptable limits (see blood clotting and anticoagulation ). With EPO and blood doping, however, the increasing viscosity of the blood brings significant health risks. Therefore, the hematocrit values ​​in some sports federations (UCI and IAAF) were fixed at 50 % for men and 47 % in women, while about 51.5 % for men and 47% are permissible for women in Nordic skiing by the FIS, which on the hemoglobin limits 17.0 and 16.0 of g / dl actually used is based.

Patients are examined at highly elevated values ​​directly without apparent cause on polycythemia vera.

Decreased hematocrit

A low hematocrit indicates a overhydration of the patient ( for example for replacement of blood loss by pure liquids), or a loss or reduced formation of erythrocytes, the person may then also be an indication of anemia.

With endurance training, the hematocrit is reduced, because the blood volume increases more strongly than the number of red blood cells. This leads to a reduced viscosity (thickness ) of the blood. The blood rubs less on the walls of the blood vessels so the heart has to do less work. Due to the larger amount of blood plasma is the liquid reserve available to the body available for cooling, increased (see sweating).