The hematocrit (Ht) or packed cell volume (PCV) is the proportion of blood volume that is occupied by red blood cells. It is normally between 0.35 and 0.52, and slightly higher on average in males.

GoldBamboo

... Why get tested?
If your doctor suspects that you have anemia (too few red blood cells), polycythemia (too many red blood cells), or dehydration

When to get tested?
As part of a complete blood count (CBC), which may be ordered for a variety of reasons

Sample required?
A blood sample drawn from a vein in your arm or by a fingerstick (children and adults) or heelstick (newborns)
...
Lab Tests Online - more...

The hematocrit (Ht or HCT) and packed cell volume (PCV) are measures ...
Wikipedia - [full article]

Resources