The first test method for determining hematocrit was developed by Paul M. Wintrobe (1901 - 1986). He developed the so-called "Wintrobe hematocrit tube" (Kushner 2007). This measurement method, sometimes referred to as the "macro hematocrit," served as the basis for the reference measurements that were subsequently developed (Bain 1997).
A correlation between elevated hematocrit and arterial hypertension was first described by Gaisböck in 1905 (Middeke 2005).
A hematocrit is the percentage by volume of cellular elements circulating in the blood. Since erythrocytes normally account for about 96 % of the elements circulating in the blood, the hematocrit essentially corresponds to the proportion of erythrocytes (Herold 2022).
A distinction is made between the determination of the macrohaematocrit and the microhaematocrit. The macrohaematocrit is the classic original method used by Maxwell Wintrobe to measure haematocrit. Here, 1 ml of blood is centrifuged for 30-60 min. However, this method is too slow and laborious for routine work.
The microhaematocrit method was therefore developed, in which a small amount of blood is drawn into a non-graduated tube by capillary action and then centrifuged for 5-10 min (Bain 1997).
To determine the hematocrit, blood mixed with anticoagulants (e.g. EDTA) is centrifuged at high speed (Mahlberg 2005).
Standard values:
The mean hematocrit value is approx. 47 % (± 7 %) for men and 42 % (± 5 %) for women. (Kasper 2015)
Elevated hematocrit in:
After a prolonged stay at high altitudes, erythrocyte production increases due to the lack of oxygen (Emminger 2005). This can also occur in heavy smokers due to the reduced O2 content in the tissue (Dörner 2006)
- Dehydration
- Polycythemia (Dörner 2006)
- Newborns (Mahlberg 2005)
Decreased hematocrit in:
- Hyperhydration (Dörner 2006)
- Anemia (Mahlberg 2005)
Falsely elevated hematocrit in:
- Leukocytosis > 100,000 / µl (Müller 2023)
Falsely decreased hematocrit in:
- fragmented erythrocytes
- Cold agglutinins (Müller 2023)
The hematocrit is the most important determinant of the viscosity of whole blood and is three times as high as the viscosity of blood plasma (Marino 2008). The hematocrit measured in venous blood is generally 2 % higher than the value measured in capillary blood (Dörner 2006) and the value measured in arterial blood is slightly lower than that measured in venous blood (Mahlberg 2005).
Indications for determining the hematocrit:
- Anemia (Dörner 2006)
The hematocrit is calculated and is therefore less useful in anemia than the hemoglobin value, which is measured directly (Kasper 2015).
- for the diagnosis of disorders of the water balance
- to determine the erythrocyte index MCHC
- as an alternative to haemoglobin determination(Dörner 2006)
If the hematocrit is too high, there is an increase in blood viscosity, which requires a higher shear stress of the heart. This can lead to cardiac failure (Haber 2018).