Hematology



Hematology



Key Terms












Introduction to Hematology


Hematology is the study of blood, including the morphologic appearance and function of blood cells and diseases of the blood and blood-forming tissues. Before beginning a study of this chapter, it is suggested that you review the components and function of blood presented in Chapter 12.


Laboratory analysis in hematology is concerned with the examination of blood for the purpose of detecting pathologic conditions. It includes performing blood cell counts, evaluating the clotting ability of the blood, and identifying cell types. These tests are valuable tools that allow the physician to determine whether each blood component falls within its reference range.


Examples of hematologic tests include hemoglobin, hematocrit, white blood cell count, red blood cell count, differential white blood cell count, prothrombin time, erythrocyte sedimentation rate, and platelet count. Certain hematologic laboratory tests may be performed in the medical office. Advances in CLIA-waived automated blood analyzers designed for use in the medical office have made this possible. Automated blood analyzers perform laboratory tests with accurate test results in a short time. Each automated analyzer is accompanied by a detailed operating manual that explains its operation, test parameters, care, and maintenance.


The most frequently performed hematologic laboratory test is the complete blood count (CBC). A CBC is routinely performed on new patients and on patients with a pathologic condition. The test results provide valuable information to assist the physician in making a diagnosis, evaluating the patient’s progress, and regulating treatment. The tests included in a CBC are as follows:



An example of a laboratory report indicating the results of a CBC is presented in Figure 32-1.


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Figure 32-1 Computer-generated laboratory report for a complete blood count (CBC).


Putting It All into Practice


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My name is Latisha Sharpe, and I work in a multiphysician office as a laboratory technician. I have worked in the office for 2 years. My job duties include performing venipuncture, preparing blood for transport to an outside laboratory, operating laboratory equipment, and performing laboratory tests.


When I first started working in a physician’s office, the patients were apprehensive about someone new drawing their blood. This made me a little nervous because it seemed they were questioning my ability to perform the procedure. I explained to the patients that I had received the proper training. I showed that I was confident, and that I could perform the procedure with success. By doing this, I gained their trust. Before long, they were requesting that I draw their blood. image



Hemoglobin Determination


Hemoglobin (Hgb) is a major component of red blood cells. Hemoglobin transports oxygen to the tissue cells of the body and is responsible for the color of the red blood cell.


The hemoglobin determination is used to measure indirectly the oxygen-carrying capacity of the blood. The reference range for an adult female is 12 to 16 g/dL, and the reference range for an adult male is 14 to 18 g/dL. A hemoglobin determination is performed as an individual test or as part of the CBC. A hemoglobin determination is often performed as a routine test on individuals, such as children younger than 2 years of age and pregnant women, who are at risk for developing anemia.


A decreased hemoglobin level occurs with anemia (especially iron-deficiency anemia), hyperthyroidism, cirrhosis of the liver, severe hemorrhaging, hemolytic reactions, and certain systemic diseases, such as leukemia and Hodgkin disease. Increased levels of hemoglobin are present with polycythemia, chronic obstructive pulmonary disease, and congestive heart failure.


The hemoglobin determination can be performed on capillary or venous blood. Hemoglobin can be measured in the medical office using a hemoglobin analyzer. A hemoglobin analyzer permits processing of the specimen in a short time with accurate and reliable test results, allowing the physician to evaluate the condition while the patient is still at the medical office. Examples of CLIA-waived hemoglobin analyzers often used in the medical office include the Hemoglobin Hb 201+ Analyzer (HemoCue, Inc., Lake Forest, Calif.) and the Stat-Site Hgb Meter (Stanbio Laboratory, Boerne, Tex.) (Figure 32-2).


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Figure 32-2 CLIA-waived hemoglobin analyzer.

One of the primary advantages of using a hemoglobin analyzer is that it requires only a finger puncture to perform the test rather than a venous blood specimen collected through a venipuncture. The manufacturer of each hemoglobin analyzer provides an operating manual (and sometimes an instructional video) with the instrument that includes information needed to perform quality control procedures, precautions to take when running the test, and information on storage and stability of the testing devices (e.g., testing cards or cuvettes) and control reagents, collection of the specimen, and the procedure for testing the specimen. It is important that the medical assistant become completely familiar with all aspects of the hemoglobin analyzer. Quality control procedures are of particular importance to ensure that the analyzer is functioning properly, and that test results are reliable and accurate. (Refer to Chapter 29, Quality Control, to review quality control guidelines for laboratory testing.)


The medical assistant must follow the hemoglobin procedure exactly as presented in the operating manual. The basic procedure for performing a hemoglobin test involves placing a testing device in the analyzer. A skin puncture is performed on a finger, and a drop of the patient’s blood is placed on the testing device. After a countdown period in which the analyzer determines the hemoglobin test results, the hemoglobin results are displayed on the LCD screen of the analyzer. The medical assistant should record the results in the patient’s chart, including the date and time, the name of the test (hemoglobin), and the results measured in g/dL.



Hematocrit


The hematocrit (Hct) is a simple, reliable, and informative test that is frequently performed in the medical office. The word hematocrit means “to separate blood.” The solid or cellular elements are separated from the plasma by centrifuging an anticoagulated blood specimen. The heavier red blood cells become packed and settle to the bottom of a tube. The top layer contains the clear, straw-colored plasma. Between the plasma and the packed red blood cells is a small, thin, yellowish-gray layer known as the buffy coat, which contains the platelets and white blood cells (Figure 32-3).


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Figure 32-3 Hematocrit test results. The blood cells are separated from the plasma by centrifuging an anticoagulated blood specimen, and the results are read at the top of the packed cell column.

The purpose of the hematocrit is to measure the percentage volume of packed red blood cells in whole blood. The normal hematocrit range for a woman is 37% to 47%; for a man, 40% to 54%. A low hematocrit reading may indicate anemia, and a high reading may indicate polycythemia. The hematocrit, in conjunction with other hematologic tests, is an aid to the physician in the diagnosis of a patient’s condition. The hematocrit also is used as a screening measure for the early detection of anemia and is often included in a general physical examination.


The microhematocrit method is used most often in the medical office to perform a hematocrit determination. Through capillary action, blood is drawn directly from a free-flowing skin puncture into a disposable capillary tube lined with an anticoagulant. An anticoagulated blood specimen collected by venipuncture also can be used; through capillary action, the blood specimen is drawn into the capillary tube from the evacuated collection tube. After the specimen is collected, one end of the capillary tube is sealed with a commercially prepared sealing compound (e.g., Cha-Seal [Chase Scientific, Langley, Wash.], Seal-Ease [Becton Dickinson, Franklin Lakes, NJ]). The capillary tube is then placed in a microhematocrit centrifuge. The centrifuge spins the blood at an extremely high speed; only 3 to 5 minutes are required to pack the red blood cells. The results are read at the top of the packed cell column. Procedure 32-1 describes how to perform a hematocrit determination.



imageProcedure 32-1   Hematocrit image image image



Outcome


Perform a hematocrit determination.



Equipment/Supplies





1. Procedural Step. Sanitize your hands. Greet the patient and introduce yourself. Identify the patient by full name and date of birth, and explain the procedure.


2. Procedural Step. Assemble equipment. Open the gauze packet. Cleanse the puncture site with an antiseptic wipe, and allow it to air-dry. Apply gloves and perform a finger puncture, then dispose of the lancet in a biohazard sharps container.


    Principle. Personal protective equipment and proper disposal of the lancet are required by the OSHA standard to prevent exposure to bloodborne pathogens.


3. Procedural Step. Wipe away the first drop of blood with a gauze pad. Fill the first capillary tube by holding one end of it horizontally, but slightly downward, next to the free-flowing puncture. Keep the tip of the capillary tube in the blood, but do not allow it to press against the patient’s skin. Calibrated tubes are filled to the calibration line; uncalibrated tubes are filled approximately three quarters (within 10 to 20 mm of the end of the tube). The blood is drawn into the tube through capillary action. Fill a second tube using the method just described. Place a gauze pad over the puncture site and apply pressure.


    Principle. Not keeping the tip of the capillary tube in the blood can cause air bubbles in the stem of the tube, which leads to inaccurate test results. Allowing the capillary tube to press against the skin closes the opening of the capillary tubes and does not allow blood to enter. The type of tube (calibrated or uncalibrated) is based on the method used to read the test results. The hematocrit should be performed in duplicate to ensure accurate and reliable test results.


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Fill the capillary tube.

4. Procedural Step. Push the dry end of the tube (end opposite the filling end that does not contain blood) down into the sealing compound. This seals the end of the capillary tube. The sealing compound can be used to hold the capillary tubes until they are ready to be placed in the microhematocrit centrifuge. To do this, the sealing compound should be placed on a flat surface with the tubes in a vertical position. Before removing a capillary tube from the sealing compound, rotate the tube between the thumb and index finger to prevent the sealing compound from pulling out when the tube is lifted out of the sealing compound.


    Principle. Blood in the capillary tube at the end being sealed prevents a successful closure, which may cause leakage of the blood specimen, leading to inaccurate test results. Capillary tubes must be sealed properly to prevent leakage of the blood specimen during centrifugation.


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Seal one end of the tube.

5. Procedural Step. Check the patient’s puncture site for bleeding and apply an adhesive bandage, if needed.


6. Procedural Step. Place the capillary tubes in the microhematocrit centrifuge with the sealed end facing out. Balance one tube with the other capillary tube placed on the opposite side of the centrifuge.


    Principle. Placing the sealed end toward the outside prevents the blood specimen from spinning out of the capillary tube when the centrifuge is in operation.


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Place the tube in the centrifuge.

7. Procedural Step. Place the cover on the centrifuge, and lock it securely. Centrifuge the blood specimen for 3 to 5 minutes at a speed of 10,000 rpm.


    Principle. Centrifuging the blood specimen causes the red blood cells to become packed and to settle on the bottom of the tube.


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Align the bottom of the red cell column with the 0 line.

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Read the results.

8. Procedural Step. Allow the centrifuge to come to a complete stop. Read the results, as follows:



In both cases, the buffy coat should not be included in the reading. The answer represents the percentage of blood volume occupied by the red blood cells. (The hematocrit determination on this reading device is 38.)


Principle. Stopping the centrifuge with your hands can injure you and can damage the machine.


9. Procedural Step. Read the second tube in the manner just described; the results of the tubes should agree within 4 percentage points. If not, the hematocrit procedure must be repeated. If they are within 4 percentage points, the two values are averaged to derive the test results.


10. Procedural Step. Properly dispose of the capillary tubes in a biohazard sharps container. Remove gloves and sanitize your hands. Chart the results. Include the date and time and the hematocrit results.


11. Procedural Step. Return the equipment to its proper storage place. Store the sealing compound at room temperature. Exposing it to a temperature above 80° F adversely affects its consistency.


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Apr 16, 2017 | Posted by in NURSING | Comments Off on Hematology

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