CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
• Hematocrit (relative volume of erythrocytes) (Hct)
• Mean corpuscular (erythrocyte) volume (MCV)
• Mean corpuscular (erythrocyte) Hgb (MCH) (pg)
• Mean corpuscular (erythrocyte) Hgb concentration
(MCHC) (g/L)
• Platelet or thrombocyte count (platelets) (10 9 /L)
The MCV, MCH, and MCHC, which are called the RBC indices, are calculated
from the RBC count, along with the Hgb and Hct values.
Because WBCs are normally less than 10,000 per microliter in number,
whereas RBCs number in the millions per microliter, counting both WBCs
and RBCs makes little difference in the final RBC count. After the RBCs are
counted, they are then lysed, or destroyed, so the solution contains intact
WBCs, which are counted in the same manner as the RBCs. The resulting
solution of lysed RBCs and WBCs can now be used to measure the Hgb, by
determining the absorbance* or concentration of the solution of lysed RBCs
from which the Hgb went into solution. The automated cell counter efficiently
performs all of these processes and calculations in a matter of seconds. However,
all of the tests may be performed manually, and most laboratory training
programs teach manual methodology for the student to understand the
processes, as well as to provide backup for an uninterrupted workflow during
emergencies.
Coagulation Procedures
Normally, a person’s blood should not coagulate as it passes through the vascular
system, as the results would be disastrous if clots spontaneously occurred in the
vessels of vital organs of the body. However, sometimes clotting needs to occur
to prevent hemorrhage, so the body is constantly juggling anti coagulant factors
as well as coagulation factors to maintain homeostasis. To prevent strokes and
heart attacks, it is sometimes necessary to manipulate the body’s coagulation
system to prevent clots and to prolong the time required for a clot to form. The
multitude of factors involved in inhibiting or stimulating clotting at the appropriate
time are covered at length in courses for hematology and coagulation.
This section will provide the student an overview of the most basic tests and
their meanings.
Clotting involves intrinsic factors found in the plasma of the blood and an
extrinsic factor from the tissue called thromboplastin. When a fibrin clot begins
to form when tissue is damaged by injury, platelets also become enmeshed in the
clot, to strengthen it and solidify it. It is later necessary for the body to dissolve
*
Absorbance is determined by an instrument called a spectrophotometer, which measures the
amount of light absorbed by a solution of colored molecules; the amount of light absorbed
is also known as optical density, or OD. This measurement, which directly determines the
concentration of colored molecules within a solution, is widely used for clinical laboratory
determinations.
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