The purpose of the hematocrit or packed cell volume (PCV) test is to determine the percentage of red blood cells in whole blood. The hematocrit is reported as a percentage because it is the proportion of red blood cells compared to the amount of plasma in whole blood. The term "hematocrit" literally means to separate blood. A sample of blood is placed in a tube that contains an anticoagulant, which prevents clotting. The sample is mixed, and three distinct layers will separate out. The bottom layer represents the hematocrit value and is composed of red blood cells, approximately 45% of the total blood volume, with variations allowed for men and women. The middle layer is a thin, whitish layer called the buffy coat, approximately 1% of the blood volume, which is made up of white blood cells and platelets . The upper layer is the liquid plasma, which comprises the remainder of the total blood volume.
Women 37-47% (in pregnancy : >33%)
Since the hematocrit is the percentage of red blood cells in whole blood, a decrease in hematocrit values is an indication of some type of anemia. Therefore, anything that causes a decrease in the number of red blood cells will result in a decrease in the hematocrit. Blood loss, conditions where there is increased destruction of red blood cells, leukemia, and diseases that interfere with red blood cell production will exhibit a low hematocrit. It must also be noted that overhydration, or an increase in plasma volume for any reason, can result in a relative decreased hematocrit value. An apparent increase in the hematocrit must be closely analyzed. Since the hematocrit is reported as a percentage of red blood cells to blood volume, any decrease in the volume of plasma would result in a mathematical increase in the hematocrit. Therefore, if the patient has lost blood plasma, the blood will be very concentrated and the hematocrit will be increased. When an increase in hematocrit is related to the increase in the actual number of red blood cells, erythrocytosis or polycythemia is the result.
Interfering Circumstances. Factors that can influence hematocrit results include age, pregnancy, gender, and living in high altitudes .
SI units Conversion Calculator. Convert Hematocrit (HCT) level to %, L/L, Proportion of 1.0, volume fraction. Clinical laboratory units online conversion from conventional or traditional units to Si units. Table of conversion factors for Hematocrit (HCT) unit conversion to %, L/L, Proportion of 1.0, volume fraction.