modifications of the Sahli-Hellige method, and 100 percent may be equal to from 13.8 g to 17.3 g. In the sets usually used in the Navy, however, 100 percent is equal to 14.5 g of hemoglobin per 100 ml of whole blood. After reading the percentage on the scale, turn the tube and read from the other side to get the equivalent reading in grams.
If either scale is hard to read, remember that 100% ÷ 14.5 g = 6.9, so one gram of hemoglobin is equal to 6.9 percent. If only one scale can be read, the other reading can be computed.
Caution: Equipment must be clean and dry before determination is started. Wipe all blood from the outside of the pipette before you insert it into the tube. Twenty cubic millimeters is a small volume, and a few blood cells clinging to the outside of the pipette can cause a significant error in findings.
HEMATOCRIT (PACKED CELL VOLUME) DETERMINATION
Hematocrit is the volume of erythrocytes expressed as a percentage of the volume of whole blood in a sample. The venous hematocrit agrees closely with the hematocrit obtained from a skin puncture; both are greater than the total body hematocrit. Dried heparin, balanced oxalate, or EDTA is satisfactory as an anticoagulant.
Although the microhematocrit method is not available at all duty stations, it is the most accurate means of determining blood volume and should be used whenever feasible. This test is rapidly replacing the red cell count for general purposes since it is easier, quicker, and more accurate. The method described here is the microhematocrit method.
Normal Values. The normal hernatocrit for males is 42 to 50 percent, for females, 40 to 48 percent. A value below an individual’s normal range for sex and age indicates anemia.
Materials Required
Procedures
1. Fill the capillary tube two-thirds to three quarters full with well-mixed, oxalated venous blood or fingertip blood (for fingertip blood use heparinized tubes, and invert several times to mix).
2. Seal one end of the tube with clay or seal the empty end of the tube in a small flame of a microburner.
3. Place the filled tube in the microhematocrit centrifuge, with the plugged end away from the center of the centrifuge.
4. Centrifuge at a preset speed of 10,000 to 12,000 rpm for 5 minutes. If the hematocrit exceeds 50 percent, centrifuge for an additional 3 minutes.
5. Place the tube in the microhematocrit reader. Read the hematocrit by following the manufacturer’s instruction on the microhematocrit reading device.
WHITE BLOOD CELL (LEUKOCYTE) COUNT
The total white cell count determines the number of white cells per cubic millimeter of blood. A great deal of information can be derived from white cell studies. The white cell count and the differential count are common laboratory tests and almost a necessity in determining the nature and severity of systemic infections.
Normal Values. The normal range is 4,000 to 11,000 cells per cubic millimeter of whole blood.
Abnormal White Blood Cell Count
1. Leukocytosis (abnormally high count).
This may be caused by:
a. Systemic or local infections (usually due to bacteria). These counts are highly variable and not diagnostic. Some infections and representative white cell counts are:
(1) pneumonia—20,000 to 30,000/mm3
(2) meningitis—20,000 to 30,000/mm3
(3) appendicitis— 10,000 to 30,000/ mm3
b. Dyscrasia of blood-forming tissues. This is not caused by any known bacteria, but is due to a malfunctioning of the marrow and lymph tissues, resulting in extremely high white cell counts, which sometimes exceed 1,000,000/mm3. This is commonly known as leukemia, or blood cancer.