Hematocrit

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Two blood samples, freshly taken on the right, with sedimented cellular components on the left. This part is the hematocrit.

Hematocrit (abbreviation: Hct , Hkt or Hk ) describes the proportion of red blood cells (erythrocytes) in the volume of the blood. Since the erythrocytes physiologically represent 99 percent of the total volume of the blood cells, the hematocrit value corresponds approximately to the proportion of the cell volume (PCV, Packed Cell Volume), i.e. the cellular components, in the blood volume. In addition, the hematocrit value can provide information about the patient's water balance.

The hematocrit is determined by centrifuging a clot-free blood sample in a tube. The coagulation ( hemostasis ) of the blood is prevented by adding EDTA (ethylenediaminetetraacetate) or heparin . The heavier red blood cells are separated from the plasma , the height of the erythrocyte column is measured in relation to the entire blood column (consisting of erythrocytes, other cellular components and plasma). The boundaries between erythrocytes, leukocytes / platelets and blood plasma can be seen with the naked eye.

Normal values

Normal hematocrit values are between 42 and 50 percent in men and between 37 and 45 percent in women. Even after profuse bleeding, the hematocrit can be normal as both cells and fluid are lost.

In other vertebrates , the hematocrit can be between 20 and 65 percent.

According to model calculations from a fluid-mechanical point of view (the viscosity of a liquid depends on the viscosity of the solvent and the volume fraction of its solid components), the optimal hematocrit value is around 40 percent. The normal hematocrit value of humans and many animal species seems to be optimal from this point of view.

If the hematocrit value deviates from the "normal values", the measured value of the blood sugar measurement can also deviate.

Increased hematocrit

A high hematocrit indicates a high percentage of erythrocytes ( polyglobulia ) or a lack of fluid (see dehydration and desiccosis ). People with greatly increased values ​​without a directly identifiable cause are also examined for polycythemia vera . There are indications that an increased hematocrit value with a high proportion of erythrocytes at the same time is due to sleep apnea, since the oxygen concentration in the blood drops sharply due to nightly breathing pauses.

Maximum values can also come about through long stays at high altitudes (e.g. when climbing at high altitude ) and can reach over 70 percent hematocrit. The viscosity of the blood is kept naturally at a tolerable level through a corresponding increase in anticoagulant enzymes (see blood clotting and anticoagulation ).

With EPO and blood doping , however, the increasing viscosity of the blood brings with it considerable health risks. Therefore, the hematocrit limit values ​​have been set by some sports associations ( UCI and IAAF ) at 50 percent for men and 47 percent for women, while in Nordic skiing the FIS allows about 51.5 percent for men and 47 percent for women, which is based on the hemoglobin limit values actually used of 17.0 or 16.0 g / dl. This regularly leads to the exclusion of athletes who either naturally have a high hematocrit value or who fluctuate more strongly on a daily basis as a result of stress and individual behavior. The example of Marco Pantani is well-known, who after a night's sleep at altitude at the Giro d'Italia had an increased hematocrit value before breakfast, while the value had been normal the day before . Pantani was then banned and could not continue the Giro.

Decreased hematocrit

Acute
A low hematocrit value indicates that the patient is overhydrating, for example after replacing blood loss with cell-free fluids. Since the loss of blood volume is much more dangerous than the loss of blood itself - and because blood transfusions are not always available outside of scheduled operations - blood losses are first treated with Ringer's solution , volume substitutes and blood plasma . Emergency patients survive very low hematocrit values ​​for a short period of time, in individual cases even with hematocrit values ​​of less than 5 percent.

Of 300 patients who refused blood transfusions (including Jehovah's Witnesses ), none died within 30 days of an operation if the hemoglobin value after the operation was 7.1 to 8 g / dL. (7.1 g / dL correspond to 53 or 60 percent of the normal hemoglobin and hematocrit values, depending on gender.) With postoperative hemoglobin values ​​between 4.1 and 5 g / dL, the mortality rate was 34.4 percent.

Chronic
A hematocrit that is too low can also indicate a (not sudden) loss or reduced formation of erythrocytes, i.e. anemia .

Sport
Exercise can cause the hematocrit value to rise significantly for a short time, which is due to the loss of water. With endurance training , however, the hematocrit is slightly reduced in the long term because the blood volume increases more than the number of red blood cells. This also leads to a reduced viscosity (viscosity) of the blood and reduces the workload of the heart because the blood experiences less frictional resistance in the arteries. Due to the larger proportion of blood plasma, the fluid reserve that is available to the body for cooling is also increased. The athlete can sweat more and longer before a loss of performance occurs.

See also

Web links

Individual evidence

  1. ↑ Georg Löffler, Petro Petrides, Peter Heinrich (Eds.): Biochemistry and Pathobiochemistry . 8th edition. Springer Medizin Verlag Heidelberg, Heidelberg 2006, ISBN 978-3-540-32680-9 , p. 955 .
  2. ↑ Harvey Lodish, Arnold Berk, Chris Kaiser, Monty Krieger, Matthew Scott, Anthony Bretscher, Hidde Ploegh: Molecular cell biology . 6th edition. 2008, ISBN 978-0-7167-7601-7 , pp. 679 .
  3. ↑ hematocrit
  4. ^ Christopher D. Moyes, Patricia M. Schulte: Tierphysiologie . Pearson Studium, Munich 2008, ISBN 978-3-8273-7270-3 , pp. 426 ( limited preview in the Google book search - English: Principles of Animal Physiology . Translated by Monika Niehaus , Sebastian Vogel).
  5. ↑ H. Stark, S. Schuster: Comparison of various approaches to calculating the optimal hematocrit in vertebrates . In: J. Appl. Physiol. , 113, 2012, pp. 355-367, doi: 10.1152 / japplphysiol.00369.2012
  6. ↑ Hematocrit value on Diabetiker-bedarf.de
  7. ↑ aerztezeitung.de
  8. ↑ Arnd Krüger : 50 percent hematocrit - an arbitrary limit . In: NZZ , June 11, 1999; LimmatsharksZürich ( Memento from October 6, 2014 in the Internet Archive )
  9. ↑ Dai et al .: Case report: intraoperative management of extreme hemodilution in a patient with a severed axillary artery. In: Anesthesia and Analgesia. 2010, accessed January 9, 2019 .
  10. ^ Carson et al .: Mortality and morbidity in patients with very low postoperative Hb levels who decline blood transfusion . In: Transfusion, 2002, PMID 12375651
  11. ↑ blood count in competitive athletes. In: Ärztezeitung. December 15, 2014, accessed June 2, 2020 .