The hematocrit test determines the percentage of whole blood that is made up of red blood cells (RBCs). A normal hematocrit test result for males is about 45% (38-50%) of blood volume. For females, it is about 40% (35-44%) of blood volume
The test results are affected by RBC number, RBC size, and plasma volume. A low test result can be produced by a low number of RBCs, microcytosis (small RBCs), or an increased plasma volume. A high test result can be produced by a high number of RBCs (polycythemia), macrocytosis (enlarged RBCs), or a low plasma volume.
1. First, a finger is lanced and a small drop of blood is allowed to accumulate.
2. Blood is drawn up into a heparinized (anticoagulant) glass tube.
3. One end of the blood-filled tube is sealed with clay.
4. The blood-filled tubes are placed in a centrifuge and spun until the plasma and formed elements separate.
5. The glass tube is moved across a reader board until the bottom of the RBC column is at 0% and the top of the plasma column is at 100%
6. The percentage of RBCs in the blood is determined by tracing the grid lines near the top of the red column to the % scale.