Step 15: Hematologic Tests

Hematologic tests, which include laboratory assessment of blood formation and blood disorders, are used to make a diagnosis, evaluate a patient’s progress and regulate treatment. The complete blood count (CBC) is the most common laboratory test in hospitals. The phlebotomist collects blood in the tube with the lavender top for a complete blood count.

CBC Includes

Hemoglobin determination (Hgb)

Hematocrit determination (Hct)

Red blood cell count

White blood cell count

Differential white blood cell count

Platelet count

Before you explore these tests in greater detail, let’s go over the methods used to count blood.

Blood Count Methods

Both automated and manual blood counts are popular. As you can imagine, red and white blood cells are concentrated in blood. Blood is diluted with fluid to allow the different types of cells to be counted.

One method involves placing the diluted blood on a hemocytometer—a heavy glass slide used to count blood cells. The hemocytometer has three depressions, two raised platforms and ruled lines that are etched in the glass. In addition, a cover slip is placed over the ruled portions to control the depth of the fluid. The ruled areas allow the red and white blood cells to be counted under a microscope.

Another common way to examine blood is through a blood smear of either capillary or venous blood. Blood is smeared on a glass slide and then stained. Many offices use the Wright’s stain which causes each different type of cell to show up in a different color. After staining, the slide is examined under a microscope. The red and white blood cells and platelets can be examined for size, shape and counts.

Steps to Take: Blood Smear

1. Wash your hands.
2. Make sure supplies are nearby, and put on gloves and protective equipment. Label two slides with the patient’s name and the date.
3. Identify the patient and explain the procedure.
4. Perform a capillary puncture.
5. Wipe away the first drop of blood and wait for a second drop to form. Touch the drop of blood to the slide, but don’t allow the finger to touch the slide. Position the finger so the blood drops 1/4 inch from the frosted end.
6. Pick up another slide, which will be your spreader slide. Hold it at a 30- to 35-degree angle and bring it against the slide with the blood.
7. Using a gliding motion, spread blood over 3/4 of the slide. Create a feathered edge.
8. Allow the slide to air dry.
9. Dispose of gloves in the biohazard container.
10. Wash your hands.
11. Document the procedure.

Online Learning

Here’s an example video of how to take Peripheral Blood Smears.

Many healthcare facilities use automated cell counters, which detect and count blood cells through the use of electricity. The blood is diluted with an electrically charged fluid. As each cell of the diluted blood moves through the machine’s counting chamber, it interrupts the flow of electricity. Each interruption is counted, thus determining the number of blood cells in the sample.

The hemocytometer and the automated cell counter are both used to count blood cells. However, there are many other types of tests that can be conducted on blood. Two of these are the hemoglobin and hematocrit tests.

Hemoglobin Test

The hemoglobin (Hgb) test is part of a complete blood count, but can also be ordered individually. Hemoglobin makes up 85 percent of the dry weight of normal red blood cells. The main function of hemoglobin, a protein molecule, is to transport oxygen and carbon dioxide to and from the lungs to the body’s organ and tissue cells. Hemoglobin delivers about 95 percent of all oxygen to cells and returns about 27 percent of the body’s carbon dioxide to the lungs to be removed.

Hemoglobin is measured using a hemoglobinometer, which measures the amount of hemoglobin in a fluid by comparing it with a solution of known strength and of normal color. Hemoglobinometers work by measuring the density of the hemoglobin pigment using light. The more hemoglobin, the more light is refracted. A Hemocue is a portable hemoglobinometer device.

Normal Hemoglobin Values
Newborn	15-20 g/dL
Three months	9-14 g/dL
Ten months	12-14.5 g/dL
Adult woman	12-16 g/dL
Adult man	13-18 g/dL

Now let’s look at another test that provides information on red blood cells compared to the rest of the blood sample, the hematocrit.

Hematocrit Test

Hematocrit (Hct) is the ratio of the volume of packed red blood cells in relation to the whole blood specimen.

To test the hematocrit percentage, you could use a manual or automated test. Most medical practices use the manual method, which involves drawing a few drops of capillary blood into a microhematocrit tube. The tubes are then placed in a microhematocrit centrifuge.

Normal Hematocrit Values
Newborn	45-60%
One year	27-44%
Adult female	36-46%
Adult males	40-55%

In order to test for hematocrit levels, the blood specimen is centrifuged at high speeds. This allows the blood to separate into layers. The red blood cells (RBCs), the largest component of blood, fall to the bottom because they’re the heaviest and will appear as a red layer. Second is the whitish-tan buffy coat, which is made up of white blood cells and platelets. Lastly, the plasma, which is almost colorless, lies on top and is often difficult to see.

Layers of blood in a microhematocrit tube after centrifuge

A microcuvette is a single-use sample collection device for the HemoCue. When the tip of a microcuvette touches a drop of sample, it automatically draws the precise amount needed into a tiny mixing cavity.

Virtual Lab: Hemoglobin

 

 

Equipment Needed: HemoCue, lancet, microcuvette, alcohol swab, dry cotton balls, gloves, sharps container, band aid

 

 

1. Wash your hands.
2. Identify the patient and explain the procedure.
3. Put on gloves and safety glasses.
4. Select the middle or ring finger for puncture site.
5. Cleanse and disinfect the site with an alcohol swab. Allow to air dry.
6. Pull the skin at the site taut. Do not squeeze the fingertip.
7. Puncture the skin in one quick motion at the tip of the fleshy pad, slightly to the side of the end of the finger.
8. The first drop of blood is wiped away with a dry gauze or cotton ball because it contains tissue fluid which dilutes the blood drop.
9. Holding the microcuvette nearly horizontal and slightly downward, touch the tip to the drop of blood. If the flow of blood begins to slow, rewipe the puncture site with a dry gauze pad.
10. Give the patient a gauze pad or cotton ball to press onto the puncture site. Apply a band aid. Dispose of the lancet in a nearby sharps container.
11. Place the microcuvette into hemoCue and start the machine.
12. When the machine is finished, document the results.
13. Dispose of the supplies in a biohazard container.
14. Wash your hands.

Serum Collection

Serum is another common blood component that is used for testing. Serum is the liquid left over after blood has clotted. The clotting process converts fibrinogen in plasma into fibrin, which is the substance that holds the clot together. Serum is simply plasma after fibrinogen has been removed from it by the clotting process. It is also a whitish-tan color and requires the use of a centrifuge to collect.

Virtual Lab: Serum from Whole Blood

 

 

Equipment Needed: Centrifuge, transport tube, clotted blood sample, gloves

1. After you have collected the blood sample in a serum separator tube, invert the tube 5 to 10 times to mix the blood with the additives in the tube.
2. Allow the tube to clot upright in the rack for 30 to 60 minutes, but no longer.
3. Place the tube in a centrifuge and spin at 2,500 rmp for 15 minutes.
4. The separating gel moves up to separate the serum from the blood cells, so you do not need to remove the tube immediately after centrifuge is completed.
5. Before you remove any samples from the centrifuges, put on a fresh pair of gloves.
6. Wait for the centrifuge to completely stop spinning.
7. Transfer the serum that has risen to the top of the tube to a plastic transport vial for pick up by the laboratory.
8. Make sure that you put the right color top back on each tube and that each tube is completely closed.
9. Serum may be collected in a tube with a plain red top, a marbled red and gray top (also called a tiger tube) or a red and black mono jet top if the testing is required stat or immediately. A tiger tube is also called a serum separator tube. You will see this abbreviated as SST.
10. When you are finished, remember to properly dispose of your gloves.
11. Label the transfer tube and complete a laboratory requisition.

Let’s look at another blood count test using white blood cells.

White Blood Cells

White blood cells (WBCs), or leukocytes, fight infection and produce antibodies for the immune system. White blood cell counts can be done with automated machinery or manually. This section will cover the background and function of WBCs.

White blood cell granulocyte

Unlike red blood cells, WBCs leave the blood vessels to fight infection. There are five different types of white blood cells that are categorized as either granulocytes or agranulocytes. Granulocytes have granules—these are the neutrophils, basophils and eosinophils types. Agranulocytes, on the other hand, don’t have granules and consist of the lymphocytes and monocytes.

Leukocyte Count Values (Cells/mm3)
Newborn	9,000-30,000
One year	6,000-14,000
Six years	4,500-12,000
Adult	4,500-11,000

WBCs use phagocytosis, detoxification, inflammation and immune response to fight infection. Each of these functions performs a different method of defense.

• Phagocytosis is the process of engulfing bacteria or particles. The WBCs primarily involved are the neutrophils and monocytes, which then destroy the particle with enzymes.
• Detoxification occurs when eosinophils neutralize poisons and other harmful substances. Eosinophils use the detoxification process to control histamine production, resulting in allergic reactions.
• Inflammation (swelling, heat, redness and pain) is the body’s response to any foreign agent, whether it is a pathogen, a foreign body, trauma or extremes in temperature. Swelling is caused by increased plasma flow to the area that brings with it WBCs to fight the intruder. Basophils play a major role by releasing histamine to increase inflammation (bringing in more plasma with more leukocytes) and heparin to keep the plasma from clotting. Basophils also coordinate the entire inflammatory response so that the foreign agent is contained and eliminated, the area is cleaned of any dead tissue and healing can begin.
• The immune response is a complicated process of using specific antibodies to fight different antigens that invade the body. The immune system “remembers” these adapted antibodies so they are available if the pathogen returns. This memory process is known as immunity.

Abnormal WBC counts can be a sign of serious illness. Review the illnesses associated with an increase in specific leukocyte counts.