b. Hematocrit (Packed Cell Volume). The hematocrit is the volume of
erythrocytes expressed as a percentage of whole blood in a sample. An anticoagulant
is added to a small blood sample, and the tube is tightly capped to avoid evaporation.
The sample is placed on a centrifuge and turned for five to thirty minutes (depending on
the method and equipment used). The red cell column is measured in height
(millimeters) against the height (in millimeters) of the whole column. The normal
hematocrit for males is between 40 and 54. For females, the normal range is between
38 and 47. A value below the patient's normal or below the normal range may indicate
anemia. A higher reading may indicate polycythemia.
c. Hemoglobin. The hemoglobin concentration in the blood bears a direct
relationship to its oxygen carrying capacity. Because of the relationship, this test is
performed on practically every patient, especially for suspected diseases associated
with anemia. There are several ways to measure hemoglobin. The most widely used
and recommended method uses cyanide compounds to convert the hemoglobin. This
process will eventually result in a compound called "cyanmethemoglobin". The
hemoglobin content can then be determined. The use of cyanide compounds in this
process increases the danger of accidental poisoning in the laboratory. Proper
ventilation and protection for the technician must be available. The normal values are
14 to 17 grams hemoglobin (per deciliter) for adult males and 12 to 16 grams
hemoglobin (per deciliter) for adult females.
d. Erythrocyte Sedimentation Rate. The erythrocyte sedimentation measures
the rate at which the red blood cells settle out of the cellular-plasma suspension. The
rate is usually increased in inflammatory infections, toxemia, cell or tissue destruction,
severe anemia, active tuberculosis, syphilis, acute coronary thrombosis, rheumatoid
arthritis, and malignant processes. The rate is generally decreased by sickle cell
anemia, polycythemia, hypofibrinogenemia, and certain drugs. The procedure is to
place a measured amount of anticoagulated blood in a tube and measure the distance
the erythrocytes fall within a given time interval. Normal values are 0 to 9 millimeters for
adult males and 0 to 20 millimeters for adult females. This test is inconclusive. It
indicates the need for further testing. In some cases, such as acute rheumatic fever or
congestive heart failure, the sedimentation rate has remained within normal limits.
e. Partial Thromboplastin Time. The partial thromboplastin time is the most
useful screening method for detecting blood coagulation disorders. This procedure
tests all three stages of blood coagulation and can show abnormalities in almost all of
the clotting factors. Freshly collected blood is combined with certain compounds and
observed for clot formation. Using most commercially prepared and some laboratory
prepared compound, the clot should form in less than 35 seconds to be considered
normal.
MD0564
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