Hematocrit

The hematocrit (Ht or HCT) and packed cell volume (PCV) are measures of the proportion of bloodvolume that is occupied by red blood cells. It is normally between 0.42 and 0.52 for males and between 0.36 and 0.48 for women[1].

Image:Packedcellvolume diagram.png

The packed cell volume can be determined by centrifuging. Heparinizedblood in a capillary tube(a.k.a. a microhematocrit tube) is typically centrifuged at 10,000 RPM for five minutes.[2]This separates the blood into layers. The volume of packed red blood cells, divided by the total volume of the blood sample gives the PCV. Because a tube is used this can be calculated by measuring the lengths of the layers.

With modern lab equipment the hematocrit is calculated by an automated analyserand not directly measured. It is determined by multiplying the red cell count by the mean cell volume. The hematocrit is slightly more accurate as the PCV includes small amounts of plasma trapped between the red cells. An estimated hematocrit as a percentage may be derived by multiplying the hemoglobinlevel in g/dL times three and dropping the units. [3].

The hematocrit is not usually considered an important consideration when looking at a person's full blood countresults as most people are more concerned with the hemoglobinconcentration and mean cell volume. However, the hematocrit gives an indication of how concentrated the red cells are in the blood - this gives an indirect impression of whether the patient is dehydrated and also how relevant the measured hemoglobin level is.

For example, there have been cases where the blood for testing was inadvertently drawn from the same arm with the intravenous line running in a transfusion of packed red cells. In this sample, the hemoglobin measurement will be high because it is measuring the fluid being transfused (i.e. mostly red cells) rather than the diluted serum. In this case, the hematocrit measurement will be artifactually very high.

In mammals, hematocrit is independent of body size.

Elevated hematocrit

In cases of dengue, where the full blood count is done daily, the hematocrit is monitored as a high hematocrit is a danger sign of an increased risk of dengue shock syndrome.

Polycythemia verais associated with elevated hematocrit.

Chronic obstructive pulmonary disease (and other pulmonary conditions associate with hypoxia) may elicit an increased production of red blood cells. This increase is mediated by the increased levels of erythropoyetin by the kidneys in response to hypoxia.

Lowered hematocrit

Lowered hematocrit can imply significant hemorrhage(for example, in an ectopic pregnancy.)

See also

• Hematology
• Blood testsde:Hämatokrit

es:Hematocrito fr:Hématocrite it:Ematocrita nl:Hematocriet pl:Hematokryt ru:??????????

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It uses material from the http://en.wikipedia.org/wiki/Hematocrit Wikipedia article Hematocrit.