Hematocrit

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 macro- and microhematocrit. The macrohematocrit represents the classic original method of Maxwell Wintrobe for hematocrit measurement. Here, 1 ml of blood is centrifuged for 30 - 60 min. However, this method is too slow and laborious for routine work.

Therefore, the determination of the microhematocrit was developed, in which a small amount of blood is aspirated by capillary action into a non-graduated tube and then centrifuged for 5 - 10 min (Bain 1997).

To determine the hematocrit, a blood mixed with anticoagulants (e.g. EDTA) is centrifuged at high speed (Mahlberg 2005).

Standard Values:

The mean hematocrit value is approximately 47% (plus / minus 7%) in men and 42% (plus / minus 5%) in women.

(Kasper 2015)

Increased hematocrit in:

- Polyglobulia

After prolonged exposure to high altitude, there is an increase in erythrocyte production due to oxygen deprivation (Emminger 2005). This can also occur in heavy smokers due to the decreased O2 content in the tissues (Dörner 2006).

- dehydration

- Polycythemia (Dörner 2006)

- Newborns (Mahlberg 2005)

Decreased hematocrit in:

- Hyperhydration (Dörner 2006)

- Anemia (Mahlberg 2005)

False elevated hematocrit in:

- Leukocytosis > 100.000 / µl (Müller 2023)

False low hematocrit in case of:

- fragmented erythrocytes

- spherocytosis

- cold agglutinins (Müller 2023)

Hematocrit represents the most important determinant of the viscosity of whole blood and is 3 times higher than the viscosity of blood plasma (Marino 2008). The hematocrit measured in venous blood is usually 2% higher than the value measured in capillary blood (Dörner 2006) and the value measured in arterial blood is slightly lower than that in venous blood (Mahlberg 2005).

Indications for determination of hematocrit:

- polyglobulia

- 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 disturbances of the water balance

- for the determination of the erythrocyte index MCHC

- as an alternative to the determination of hemoglobin(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).

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