HEMATOCRIT, ERYTHROCYTE SEDIMENTATION RATE, AND HEMOGLOBIN
Section I. HEMATOCRIT
a. The hematocrit or the packed-cell volume is the percentage of the total
volume of red blood cells in relation to the total volume of whole blood. The term
"hematocrit" is derived from two Greek words: Hemato, meaning blood; and Krites,
meaning to judge (then reduced to crit, meaning to separate). The procedure is
performed by filling a capillary tube with blood and centrifuging at a constant speed for a
constant period of time. The packet cell volume is then measured. The hematocrit can
also be determined by automated sequential analyzers but is usually a calculated value.
b. The hematocrit is the most useful single index for determining the degree of
anemia or polycythemia. It can be the most accurate (2-4 percent error) of all
hematological determinations. In contrast, the direct red blood cell chamber count has
a percent error of 8-10 percent. The hematocrit is, therefore, preferable to the red blood
cell count as a screening test for anemia. The values for the hematocrit closely parallel
the values for the hemoglobin and red blood cell count.
a. Principle. A capillary tube is filled with whole blood by capillary action to
within 1 to 2 cm of the end. The unfilled end is sealed and the tube is centrifuged. After
centrifugation, the capillary tube is placed in a reading device and the hematocrit value
(1) If anticoagulated venous blood is the specimen, fill a plain capillary tube
with blood. If blood without anticoagulant is used, fill a heparinized capillary tube with
the blood specimen. A heparinized capillary tube is identified by red line on the tube
specimen. A heparinized capillary tube is identified by a red line on the tube.
(2) Allow blood to enter two capillary tubes until they are approximately 2/3
filled with blood. (Air bubbles denote poor technique, but do not affect the results of the
Seal the unfilled ends of the tubes with clay.
(4) Place the two hematocrit tubes in the radial grooves of the centrifuge
head exactly opposite each other, with the sealed end away from the center of the