Hematocrit is the portion of the blood occupied by erythrocytes. It may be determined by subjecting blood to sufficient centrifugal force to pack the cells into as small a volume as possible. Cell counters calculate the hematocrit from the erythrocyte count and mean corpuscular volume:
HEMATOCRIT = ERYTHROCYTE COUNT (x 1012/L) x MCV (x 10-15 L)
This calculation is possible because the erythrocytes show Gaussian distribution in the peripheral blood with regard to their volume.
Determination of the hematocrit requires an anticoagulant, such as K3EDTA, that does not change the volume of the erythrocytes.
The errors in estimating hematocrit by centrifugation arise because of hemoconcentration due to prolonged tourniquet application during venipuncture, excessive K3EDTA, changes in the cell volume induced by preparing blood for the determination, inadequate mixing of the sample, inadequate centrifugation time or speed, or the operator’s error. Microhematocrits from the blood containing abnormal erythrocytes (sickle cell anemia, thalassemia, spherocytosis, macrocytosis) are relatively increased because of enhanced plasma trapping that is generally due to increased red cell rigidity. Fully oxygenated blood also has about 2% lower hematocrit than deoxygenated blood.
Reference values:
|
Reference range |
Units |
Boys 8 - 12 years |
0.37 - 0.45 |
1/1 |
Boys 13 - 18 years |
0.39 - 0.49 |
1/1 |
Girls 8 - 18 years |
0.35 – 0.45 |
1/1 |
Women |
0.36 – 0.47 |
1/1 |
Men |
0.42 – 0.53 |
1/1 |
|
