Blood Studies: Hematology and Coagulation
OVERVIEW OF BASIC BLOOD HEMATOLOGY AND COAGULATION TESTS
Composition of Blood
The average person circulates about 5 L of blood (1/13 of body weight), of which 3 L is plasma and 2 L is cells. Plasma fluid derives from the intestines and lymphatic systems and provides a vehicle for cell movement. The cells are produced primarily by bone marrow and account for blood “solids.” Blood cells are classified as white cells (leukocytes), red cells (erythrocytes), and platelets (thrombocytes). White cells are further categorized as granulocytes, lymphocytes, monocytes, eosinophils, and basophils.
Before birth, hematopoiesis occurs in the liver. In midfetal life, the spleen and lymph nodes play a minor role in cell production. Shortly after birth, hematopoiesis in the liver ceases, and the bone marrow is the only site of production of erythrocytes, granulocytes, and platelets. B lymphocytes are produced in the marrow and in the secondary lymphoid organs; T lymphocytes are produced in the thymus.
Blood Tests
Tests in this chapter are basic screening tests that address disorders of hemoglobin (Hb) and cell production (hematopoiesis), synthesis, and function. Blood and bone marrow examinations constitute the major means of determining certain blood disorders (anemias, leukemia and porphyrias disorders, abnormal bleeding and clotting), inflammation, infection, and inherited disorders of red blood cells,
white blood cells, and platelets. Specimens are obtained through capillary skin punctures (finger, toe, heel), dried blood samples, arterial or venous sampling, or bone marrow aspiration. Specimens may be tested by automated or manual hematology instrumentation and evaluation.
white blood cells, and platelets. Specimens are obtained through capillary skin punctures (finger, toe, heel), dried blood samples, arterial or venous sampling, or bone marrow aspiration. Specimens may be tested by automated or manual hematology instrumentation and evaluation.
BLOOD SPECIMEN COLLECTION PROCEDURES
Proper specimen collection presumes correct technique and accurate timing when necessary. Most hematology tests use liquid ethylenediaminetetraacetic acid (EDTA) as an anticoagulant. Tubes with anticoagulants should be gently but completely inverted end over end 7 to 10 times after collection. This action ensures complete mixing of anticoagulants with blood to prevent clot formation. Even slightly clotted blood invalidates the test, and the sample must be redrawn.
For plasma coagulator studies, such as prothrombin time (PT) and partial thromboplastin time (PTT), the tube must be allowed to fill to its capacity or an improper blood-to-anticoagulant ratio will invalidate coagulator results. Invert 7 to 10 times to prevent clotting.
Capillary Puncture (Skin Puncture)Capillary blood is preferred for a peripheral blood smear and can also be used for other hematology studies. Adult capillary blood samples require a skin puncture, usually of the fingertip. For children, the tip of the finger is also often the choice. Infants younger than 1 year of age and neonates yield the best samples from the great toe or side of the heel.
Procedure
Capillary Blood
Observe standard precautions (see Appendix A). Check for latex allergy. If allergy is present, do not use latex-containing products.
Obtain capillary blood from fingertips or earlobes (adults) or from the great toe or heel (infants). Avoid using the lateral aspect of the heel where the plantar artery is located.
Disinfect puncture site, dry the site, and puncture skin with sterile disposable lancet, perpendicular to the lines of the patient’s fingers, no deeper than 2 mm. If chlorhexidine is used, allow to dry thoroughly.
Wipe away the initial drop of blood. Collect subsequent drops in a microtube or prepare a smear directly from a drop of blood.
After collection, apply a small amount of pressure briefly to the puncture site to prevent painful extravasation of blood into the subcutaneous tissues.
PROCEDURAL ALERT
Do not squeeze the site to obtain blood because this alters blood composition and invalidates test values.
Warming the extremity or placing it in a dependent position may facilitate specimen collection.
Dried Blood Spot
In this method, a lancet is used, and the resulting droplets of blood are collected by blotting them with filter paper directly.
Check the stability of equipment and integrity of supplies when doing a finger stick. If provided, check the humidity indicator patch on the filter paper card. If the humidity circle is pink, do not use this filter paper card. The humidity indicator must be blue to ensure specimen integrity.
After wiping the first drop of blood on the gauze pad, fill and saturate each of the circles in numerical order by blotting the blood droplet with the filter paper. Do not touch the patient’s skin to the filter paper; only the blood droplet should come in contact with the filter paper.
If an adult has a cold hand, run warm water over it for approximately 3 minutes. The best flow occurs when the arm is held downward, with the hand below heart level, making effective use of gravity. If there is a problem with proper blood flow, milk the finger with gentle pressure to stimulate blood flow or attempt a second finger stick; do not attempt more than two.
When the blood circles penetrate through to the other side of the filter paper, the circles are fully saturated.
Interventions
Pretest Patient Care
Instruct patient about purpose and procedure of test.
Follow Chapter 1 guidelines for safe, effective, informed pretest care.
Posttest Patient Care
Apply small dressing or adhesive strip to site.
Evaluate puncture site for bleeding or oozing.
Apply compression or pressure to the site if it continues to bleed.
Evaluate patient’s medication history for anticoagulation, nonsteroidal anti-inflammatory drugs (NSAIDs), or acetylsalicylic acid (ASA)-type drug ingestion.
Follow Chapter 1 guidelines for safe, effective, informed posttest care.
VenipunctureVenipuncture allows procurement of larger quantities of blood for testing. Care must be taken to avoid sample hemolysis or hemoconcentration and to prevent hematoma, vein damage, infection, and discomfort. Usually, the antecubital veins are the veins of choice because of ease of access. Blood values remain constant no matter which venipuncture site is selected, so long as it is venous and not arterial blood. Sometimes, the wrist area, forearm, or dorsum of the hand or foot must be used. Blood values remain consistent for all of these venipuncture sites.
Observe standard precautions (see Appendix A). If latex allergy is suspected, use latex-free supplies and equipment.
Position and tighten a tourniquet on the upper arm to produce venous distention (congestion). For elderly persons, a tourniquet is not always recommended because of possible rupture of capillaries. Large, distended, and highly visible veins increase the risk for hematoma.
Ask the patient to close the fist in the designated arm. Do not ask patient to pump the fist because this may increase plasma potassium levels by as much as 1 to 2 mEq/L (mmol/L). Select an accessible vein.
Cleanse the puncture site, working in a circular motion from the center outward, and dry it properly with sterile gauze. Chlorhexidine must dry thoroughly.
To anchor the vein, draw the skin taut over the vein and press the thumb below the puncture site. Hold the distal end of the vein during the puncture to decrease the possibility of rolling veins.
Puncture the vein according to accepted technique. Usually, for an adult, anything smaller than a 21-gauge needle might make blood withdrawal more difficult. A Vacutainer system syringe or butterfly system may be used.
Once the vein has been entered by the collecting needle, blood will fill the attached vacuum tubes automatically because of negative pressure within the collection tube.
Remove the tourniquet before removing the needle from the puncture site or bruising will occur.
Remove needle. Apply pressure and sterile dressing strip to site.
The preservative or anticoagulant added to the collection tube depends on the test ordered. In general, most hematology tests use EDTA anticoagulant. Even slightly clotted blood invalidates the test, and the sample must be redrawn.
Take action to prevent these venipuncture errors:
Pretest errors
Improper patient identification
Failure to check patient compliance with dietary restrictions
Failure to calm patient before blood collection
Use of wrong equipment and supplies
Inappropriate method of blood collection
Procedure errors
Failure to dry site completely after cleansing with alcohol
Inserting needle with bevel side down
Using too small a needle, causing hemolysis of specimen
Venipuncture in unacceptable area (e.g., above an intravenous [IV] line)
Prolonged tourniquet application
Wrong order of tube draw
Failure to mix blood immediately that is collected in additive-containing tubes
Pulling back on syringe plunger too forcefully
Failure to release tourniquet before needle withdrawal
Posttest errors
Failure to apply pressure immediately to venipuncture site
Vigorous shaking of anticoagulated blood specimens
Forcing blood through a syringe needle into tube
Mislabeling of tubes
Failure to label specimens with infectious disease precautions as required
Failure to put date, time, and initials on requisition
Slow transport of specimens to laboratory
NOTE
A blood pressure cuff inflated to a point between systolic and diastolic pressure values can be used.
NOTE
The Vacutainer system consists of vacuum tubes (Vacutainer tubes), a tube holder, and a disposable multisample collecting needle.
Interventions
Pretest Patient Care
Instruct patient regarding sampling procedure. Assess for circulation or bleeding problems and allergy to latex. Verify with the patient any fasting requirements. Diagnostic blood tests may require certain dietary restrictions of fasting for 8 to 12 hours before test. Drugs taken by the patient should be documented because they may affect results.
Reassure patient that mild discomfort may be felt when the needle is inserted.
Place the arm in a fully extended position with palmar surface facing upward (for antecubital access).
If withdrawal of the sample is difficult, warm the extremity with warm towels or blankets. Allow the extremity to remain in a dependent position for several minutes before venipuncture. For young children, warming the draw site should be routine to distend small veins.
Be alert to provide assistance should the patient become lightheaded or faint.
Prescribed local anesthetic creams may be applied to the area before venipuncture; allow 60 seconds for light-skinned persons and 120 seconds for dark-skinned persons before performing the procedure.
Posttest Patient Care
If oozing or bleeding from the puncture site continues for more than a few minutes, elevate the area and apply a pressure dressing. Observe the patient closely. Check for anticoagulant or ASA-type ingestion. If venous bleeding is excessive and persists for longer than 10 minutes, notify the physician.
Be aware that the patient occasionally becomes dizzy, faint, or nauseated during the venipuncture. The phlebotomist must be constantly aware of the patient’s condition. If a patient feels faint, immediately remove the tourniquet and terminate the procedure. Place the patient in a supine position if possible. If the patient is sitting, lower the head between the legs and instruct the patient to breathe deeply. A cool, wet towel may be applied to the forehead and back of the neck, and, if necessary, ammonia inhalant may be applied briefly. Watch for signs of shock, such as increased heart rate and decreased blood pressure. If the patient remains unconscious, notify a physician immediately.
Prevent hematomas by using proper technique (not sticking the needle through the vein), releasing the tourniquet before the needle is withdrawn, applying sufficient pressure over the puncture site, and maintaining an extended extremity until bleeding stops. If a hematoma develops, apply a warm compress.
Assess the puncture site for signs and symptoms of infection, subcutaneous redness, pain, swelling, and tenderness.
CLINICAL ALERT
In patients with leukemia, agranulocytosis, or lowered resistance, finger-stick and earlobe punctures are more likely to cause infection and bleeding than venipunctures. Should a capillary sample be necessary, the cleansing agent should remain in contact with the skin for at least 5 to 10 minutes. Chlorhexidine is a topical antimicrobial. It should be allowed to dry. It may then be wiped off with alcohol and the site dried with sterile gauze before puncture.
Never draw blood from the same extremity being used for IV medications, fluids, or transfusions. If no other site is available, make sure the venipuncture site is below the IV site. Avoid areas that are edematous, are paralyzed, are on the same side as a mastectomy, or have infections or skin conditions present. Venipuncture may cause infection or circulatory impairment or retarded healing.
Prolonged tourniquet application causes stasis and hemoconcentration and will alter test results. If a vein cannot be found within a minute, release the tourniquet temporarily to avoid tissue necrosis.
Strenuous activity immediately before a blood sample draw can alter results because body fluids shift from the vascular bed to the tissue spaces and produce circulatory blood hemoconcentration. It may take 20 to 30 minutes of rest and reduced stress to reestablish fluid equilibrium.
Assess for interfering factors, including cellulitis, phlebitis, venous obstruction, lymphangitis, or arteriovenous fistulas or shunts.
To avoid spurious test results due to infusion of solutions, do not draw above an IV catheter. Choose a site distal to the IV line site.
After two attempts, a physician or highly trained phlebotomist should be called.
Blood samples may be drawn off central lines. The lines first must be flushed with saline before the blood draw.
Arterial PunctureArterial blood samples are necessary for arterial blood gas (ABG) determinations or when it is not possible to obtain a venous blood sample. “Arterial sticks” are usually performed by a physician or a specially trained nurse or technician because of the potential risks inherent in this procedure. Samples
are normally collected directly from the radial, brachial, or femoral arteries. If the patient has an arterial line in place (most frequently in the radial artery), samples can be drawn from the line. Be sure to record the amounts of blood withdrawn because significant amounts can be removed if frequent samples are required.
are normally collected directly from the radial, brachial, or femoral arteries. If the patient has an arterial line in place (most frequently in the radial artery), samples can be drawn from the line. Be sure to record the amounts of blood withdrawn because significant amounts can be removed if frequent samples are required.
ABG determinations are used to assess the status of oxygenation and ventilation, to evaluate the acid-base status by measuring the respiratory and nonrespiratory components, and to monitor effectiveness of therapy. The ABGs are also used to monitor critically ill patients, to establish baseline laboratory values, to detect and treat electrolyte imbalances, to titrate appropriate oxygen therapy, to qualify a patient for home oxygen use, and to assess the patient’s status in conjunction with pulmonary function testing.
Arterial puncture sites must satisfy the following requirements:
Sites must have available collateral blood flow.
Sites must be easily accessible.
Sites must be relatively nonsensitive as periarterial tissues.
Interventions
Pretest Patient Care
Assess patient for the following contraindications to an arterial stick or indwelling arterial line in a particular area:
Absence of a palpable radial artery pulse
Positive Allen’s test result, which shows only one artery supplying blood to the hand
Negative modified Allen’s test result, which indicates obstruction in the ulnar artery (i.e., compromised collateral circulation)
Cellulitis or infection at the potential site
Presence of arteriovenous fistula or shunt
Severe thrombocytopenia (platelet count 20,000/mm3)
Prolonged prothrombin time or partial thromboplastin time (>1.5 times the control is a relative contraindication)
A Doppler probe or finger pulse transducer may be used to assess circulation and perfusion in dark-skinned or uncooperative patients.
Before drawing an arterial blood sample, record the patient’s most recent hemoglobin concentration, mode and flow rate of oxygen, and temperature. If the patient has been recently suctioned or placed on a ventilator or if delivered oxygen concentrations have been changed, wait at least 15 minutes before drawing the sample. This waiting period allows circulating blood levels to return to baseline levels. Hyperthermia and hypothermia also influence oxygen release from hemoglobin at the tissue level.
Intratest Patient Care
Observe standard precautions and follow agency protocols for the procedure.
The patient assumes a sitting or supine position.
Perform a modified Allen’s test by encircling the wrist area and using pressure to obliterate the radial and ulnar pulses. Watch for the hand to blanch, and then release pressure only over the ulnar artery. If the result is positive, flushing of the hand is immediately noticed, indicating circulation to the hand is adequate. The radial artery can then be used for arterial puncture. If collateral circulation from the ulnar artery is inadequate (i.e., negative test result) and flushing of the hand is absent or slow, then another site must be chosen. An abnormal Allen’s test result may be caused by a thrombus, an arterial spasm, or a systemic problem such as shock or poor cardiac output.
Elevate the wrist area by placing a small pillow or rolled towel under the dorsal wrist area. With the patient’s palm facing upward, ask the patient to extend the fingers downward, which flexes the wrist and positions the radial artery closer to the surface.
Palpate for the artery, and maneuver the patient’s hand back and forth until a satisfactory pulse is felt.
Swab the area liberally with an antiseptic agent such as Chloraprep.
OPTIONAL: Inject the area with a small amount (<0.25 mL) of 1% plain Xylocaine, if necessary, to anesthetize site. Assess for allergy first. This allows for a second attempt without undue pain.
Prepare a 20- or 21-gauge needle on a preheparinized, self-filling syringe; puncture the artery; and collect a 3- to 5-mL sample. The arterial pressure pushes the plunger out as the syringe fills with blood. (Venous blood does not have enough pressure to fill the syringe without drawing back on the plunger.) Air bubbles in the blood sample must be expelled as quickly as possible because residual air alters ABG values. The syringe should then be capped and gently rotated to mix heparin with the blood.
When the draw is completed, withdraw the needle, and place a 4- × 4-inch absorbent bandage over the puncture site. Do not recap needles; if necessary, use the one-handed mechanical, recapping, or scoop technique or commercially available needles (e.g., B-D Safety-Glide [Franklin Lakes, NJ] or Sims Portex Pro-Vent [Keene, NH]). Maintain firm finger pressure over the site for a minimum of 5 minutes or until there is no active bleeding evident. After the bleeding stops, apply a firm pressure dressing but do not encircle the entire limb, which can restrict circulation. Leave this dressing in place for at least 24 hours. Instruct the patient to report any signs of bleeding from the site promptly and apply finger pressure if necessary.
Place the sample in an ice slurry and transport to the laboratory in a biohazard bag.
Label the sample with patient’s name, identification number, and date and time procured, and indicate the type and flow rate of O2 therapy or if the patient was on “room air.” Do not use blood for ABGs if the sample is more than 1 hour old.
In clinical settings such as the perioperative or intensive care environment, ABG studies usually include pH, PCO2, SO2, total CO2 content (TCO2), O2 content, PO2, base excess or deficit, HCO3, hemoglobin, hematocrit, and levels of chloride, sodium, and potassium.
NOTE
Do not use Xylocaine that contains epinephrine; it causes blood vessel constriction and makes the arterial puncture difficult.
NOTE
Putting the sample in an ice slurry prevents alterations in gas tensions because metabolic processes within the sample otherwise continue after blood is drawn.
CLINICAL ALERTMetabolizing blood cells can quickly alter blood gas values (primarily PaO2) at normal body temperature (37°C). This occurs much slower at 0°C (i.e., temperature of ice water). An iced sample should remain stable for at least 1 hour. Any sample not placed in ice should be tested within minutes after it is drawn or else discarded. The main effect of cellular metabolism decreases PO2. Several studies have shown a remarkable fall in PaO2 if the blood contains more than 100,000 white blood cells/mm3 (i.e., leukocyte larceny), even when the sample is on ice. A white count of this magnitude (usually in leukemia) should mandate special handling such as running the sample immediately. Alternatively, check the patient’s oxygen saturation by pulse oximetry, which is not affected by extreme leukocytosis.
CLINICAL ALERTSome patients may experience lightheadedness, nausea, or vasovagal syncope during the arterial puncture. Treat according to established protocols.
Posttest Patient Care
Posttest assessment of the puncture site and extremity includes color, motion, sensation, degree of warmth, capillary refill time, and quality of the pulse.
Frequently monitor the puncture site and dressing for arterial bleeding for several hours. The patient should not use the extremity for any vigorous activity for at least 24 hours.
Monitor the patient’s vital signs and mental function to determine adequacy of tissue oxygenation and perfusion.
The arterial puncture site must have a pressure dressing applied and should be frequently assessed for bleeding for several hours. Instruct the patient to report any bleeding from the site and to apply direct pressure to the site if necessary.
For patients requiring frequent arterial monitoring, an indwelling arterial catheter (line) may be inserted. Follow agency protocols for obtaining arterial line blood samples. The procedure varies for neonate, pediatric, and adult patients (see Arterial Blood Gas Tests in Chapter 14).
Label all specimens appropriately and document pertinent information in the health care record.
Bone Marrow AspirationBone marrow is located within cancellous bone and long bone cavities. It consists of a pattern of vessels and nerves, differentiated and undifferentiated hematopoietic cells, reticuloendothelial cells, and fatty tissue. All of these are encased by endosteum, the membrane lining the bone marrow cavity. After proliferation and maturation have occurred in the marrow, blood cells gain entrance to the blood through or between the endothelial cells of the sinus wall.
A bone marrow specimen is obtained through aspiration or biopsy or needle biopsy aspiration. A bone marrow examination is important in the evaluation of a number of hematologic disorders and infectious diseases. The presence or suspicion of a blood disorder is not always an indication for bone marrow studies. A decision to employ this procedure is made on an individual basis.
Sometimes, the aspirate does not contain hematopoietic cells. This “dry tap” occurs when hematopoietic activity is so sparse that there are no cells to be withdrawn or when the marrow contains so many tightly packed cells that they cannot be suctioned out of the marrow. In such cases, a bone marrow biopsy would be advantageous. Before the bone marrow procedure is started, a peripheral blood smear should be obtained from the patient and a differential leukocyte count done.
Procedure
Follow standard precautions. Check for latex allergy; if allergy is present, do not use latexcontaining products. Position the patient on the back or side according to site selected. The posterior iliac crest is the preferred site in all patients older than 12 to 18 months. Alternate sites include the anterior iliac crest, sternum, spinous vertebral processes T10 through L4, ribs, and tibia in children. The sternum is not generally used in children because the bone cavity is too shallow, the risk for mediastinal and cardiac perforation is too great, and the child may be uncooperative.
Clip hair if necessary, cleanse, and drape the site as for any minor surgical procedure.
Inject a local anesthetic (procaine or lidocaine). This may cause a burning sensation. At this time, a skin incision of 3 mm is often made.
Remember that the physician introduces a short, rigid, sharp-pointed needle with stylet through the periosteum into the marrow cavity.
Pass the needle-stylet combination through the incision, subcutaneous tissue, and bone cortex. The stylet is removed, and 1 to 3 mL of marrow fluid is aspirated. Alert the patient that when the stylet needle enters the marrow, he or she may experience a feeling of pressure. The patient may also feel moderate discomfort as aspiration is done, especially in the iliac crest. Use the Jamshidi needle for biopsy, although you can also use the Westerman-Jansen modification of the Vim-Silverman needle.
Remove the stylet and advance the biopsy needle with a twisting motion toward the anterosuperior iliac spine.
Rotate or “rock” the needle in several directions several times after adequate penetration of the base (3 cm) has been achieved. This “frees up” the specimen. Slowly withdraw the needle once this is done.
Push the biopsy specimen out backward from the needle. Use it to make touch preparations or immediately place in fixative. Make slide smears at the bedside.
Apply pressure to the puncture site until bleeding ceases. Dress the site.
Place specimens in biohazard bags, label properly, and route to the appropriate department.
TABLE 2.1 Normal Values for Bone Marrow* | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Clinical Implications
A specific and diagnostic bone marrow picture provides clues to many diseases. The presence, absence, and ratio of cells are characteristic of the suspected disease.
Bone marrow examination may reveal the following abnormal cell patterns:
Multiple myeloma, plasma cell myeloma, macroglobulinemia
Chronic or acute leukemias
Anemia, including megaloblastic, macrocytic, and normocytic anemias
Toxic states that produce bone marrow depression or destruction
Neoplastic diseases in which the marrow is invaded by tumor cells (metastatic carcinoma, myeloproliferative and lymphoproliferative diseases); assists in diagnosis and staging
Agranulocytosis (a decrease in the production of white cells). This occurs when bone marrow activity is severely depressed, usually as a result of radiation therapy or chemotherapeutic drugs. Implications for the patient focus on the risk for death from overwhelming infection.
Platelet dysfunction
Some types of infectious diseases, especially histoplasmosis and tuberculosis
Deficiency of body iron stores, microcytic anemia
Lipid or glycogen storage disease
Myelodysplastic syndrome (MDS) is the name of a group of conditions that occur when bloodforming cells in the bone marrow are damaged.
Interventions
Pretest Patient Care
Instruct the patient about the test procedure, purpose, benefits, and risks.
Ensure that a legal consent form is properly signed and witnessed. Bone marrow aspiration is usually contraindicated in the presence of hemophilia and other bleeding dyscrasias. However, risk versus benefit may dictate the choice made.
Reassure the patient that analgesics will be available if needed. Administer moderate sedation and analgesia, if ordered. Use an 02 sat monitor to evaluate breathing effectiveness.
Be aware that bone marrow biopsies or aspirations can be uncomfortable. Squeezing a pillow may be helpful as a distraction technique. Offer emotional support.
Observe standard precautions.
Sites used for bone marrow aspiration or biopsy affect pretest, intratest, and posttest care. Sites used include the posterosuperior iliac crest; anterior iliac crest (if the patient is very obese); sternum (not used as often with children because cavity is too shallow; danger of mediastinal and cardiac perforation is too great; and observation of procedure is associated with apprehension and lack of cooperation); vertebral spinous processes T10 through L4 and ribs; tibia (often in children); and ribs. Position according to the site selected, and assist in preparing the local anesthetic (i.e., procaine or lidocaine) for injection.
Explain to the patient the importance of remaining still during the procedure.
Posttest Patient Care
Monitor vital signs until stable and assess site for excess drainage or bleeding.
Recommend bed rest for 30 to 60 minutes; then normal activities can be resumed.
Monitor for signs and symptoms of shock (increased heart rate and decreased blood pressure).
Assess for signs and symptoms of infections (redness, swelling, pain and tenderness).
Administer analgesics or sedatives as necessary. Soreness over the puncture site for 3 to 4 days after the procedure is normal. Continued pain may indicate fracture.
Interpret test outcomes and monitor appropriately.
Follow Chapter 1 guidelines for safe, effective, informed posttest care.
CLINICAL ALERT
Complications can include bleeding and sternal fractures. Osteomyelitis or injury to heart or great vessels is rare but can occur if the sternal site is used.
Manual and pressure dressings over the puncture site usually control excessive bleeding. Remove dressing in 24 hours. Redress site if necessary.
Fever, headache, unusual pain, or redness or pus at biopsy site may indicate infection (later event). Instruct patient to report unusual symptoms to physician immediately.
The patient must remain still throughout this invasive procedure.
BASIC BLOOD TESTS
HemogramA hemogram consists of a white blood cell count (WBC), red blood cell count (RBC), hemoglobin (Hb), hematocrit (Hct), red blood cell indices, and a platelet count. A complete blood count (CBC) consists of a hemogram plus a differential WBC. Table 2.2 contains the normal values for a hemogram.
TABLE 2.2 Normal Values for Hemogram | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Complete Blood Count (CBC)The CBC is a basic screening test and is one of the most frequently ordered laboratory procedures. The findings in the CBC give valuable diagnostic information about the hematologic and other body systems, prognosis, response to treatment, and recovery. The CBC consists of a series of tests that determine number, variety, percentage, concentrations, and quality of blood cells:
White blood cell count (WBC): leukocytes fight infection
Differential white blood cell count (Diff): specific patterns of WBC
Red blood cell count (RBC): red blood cells carry O2 from lungs to blood tissues and CO2 from tissue to lungs
Hematocrit (Hct): measures RBC mass
Hemoglobin (Hb): main component of RBCs and transports O2 and CO2
Red blood cell indices: calculated values of size and Hb content of RBCs; important in anemia evaluations
Mean corpuscular volume (MCV)
Mean corpuscular hemoglobin concentration (MCHC)
Mean corpuscular hemoglobin (MCH)
Stained red cell examination (film or peripheral blood smear)
Platelet count (often included in CBC): thrombocytes are necessary for clotting and control of bleeding
Red blood cell distribution width (RDW): indicates degree variability and abnormal cell size
Mean platelet volume (MPV): index of platelet production
These tests are described in detail in the following pages.
CLINICAL ALERT
Hct of less than 20% can lead to cardiac failure and death.
Hct of greater than 60% is associated with spontaneous clotting of blood.
Hb value of less than 5.0 g/dL (<50 g/L) leads to heart failure and death.
Hb value of greater than 20.0 g/dL (>200 g/L) results in hemoconcentration and clogging of capillaries.
A critical decrease in platelet value to less than 20 × 103/mm3 (<20 × 109/L) is associated with a tendency for spontaneous bleeding, prolonged bleeding time, petechiae, and ecchymosis.
Interfering Factors
RBCs
Many physiologic variants affect outcomes: posture, exercise, age, altitude, pregnancy, and many drugs.
Hematocrit
Physiologic variants affect Hct outcomes: age, sex, and physiologic hydremia of pregnancy.
Hemoglobin
Physiologic variations affect test outcomes: high altitude, excessive fluid intake, age, pregnancy, and many drugs.
MCHC
High values may occur in newborns and infants.
Presence of leukemia or cold agglutinins may increase levels. MCHC is falsely elevated with a high blood concentration of heparin.
MCH
Hyperlipidemia and high heparin concentrations falsely elevate MCH values.
WBC counts greater than 50,000/mm3 falsely elevate Hb values and falsely elevate the MCH.
WBC Count
Hourly variation, age, exercise, pain, temperature, and anesthesia affect test results.
Neutrophils and Eosinophils
Physiologic conditions such as stress, excitement, exercise, and obstetric labor increase neutrophil levels. Steroid administration affects levels for up to 24 hours.
The eosinophil count is lowest in the morning and then rises from noon until after midnight. Do repeat tests at the same time every day. Stressful states such as burns, postoperative states, and obstetric labor decrease the count. Drugs such as steroids, epinephrine, and thyroxine affect eosinophil levels.
Platelets
Physiologic factors include high altitudes, strenuous exercise, excitement, and premenstrual and postpartum effects.
A partially clotted blood specimen affects the test outcome.
Interventions
Pretest Patient Care for Hemogram, CBC, and Differential (Diff) Count (All Components)
Explain test procedure. Explain that slight discomfort may be felt when skin is punctured. Refer to venipuncture procedure for additional information.
Avoid stress if possible because altered physiologic status influences and changes normal hemogram values.
Select hemogram components ordered at regular intervals (e.g., daily, every other day). These should be drawn consistently at the same time of day for reasons of accurate comparison; natural body rhythms cause fluctuations in laboratory values at certain times of the day.
Dehydration or overhydration can dramatically alter values; for example, large volumes of IV fluids can “dilute” the blood, and values will appear as lower counts. The presence of either of these states should be communicated to the laboratory.
Fasting is not necessary. However, fat-laden meals may alter some test results because of lipidemia.
Some medications and other substances can alter results. Obtain a current medication history from the patient.
A high WBC count or diseases that cause RBCs to agglutinate may alter test results.
Posttest Patient Care for Hemogram, CBC, and Differential (Diff) Count (All Components)
Apply manual pressure and dressings to the puncture site on removal of the needle.
Monitor the puncture site for oozing. Maintain pressure dressings on the site if necessary. Notify physician of unusual problems with bleeding. If a hematoma develops, apply a compress. If the hematoma is large, assess pulses distal to the phlebotomy site.
Resume normal activities and diet.
Bruising at the puncture site is not uncommon. Signs of inflammation are unusual and should be reported if the inflamed area appears larger, if red streaks develop, or if drainage occurs.
Evaluate the outcome and counsel the patient appropriately about anemia, polycythemia, risk for infection, and related blood disorders.
Monitor patients with serious platelet defects for signs and symptoms of gastrointestinal bleeding, hemolysis, hematuria, petechiae, vaginal bleeding, epistaxis, and bleeding from gums.
CLINICAL ALERTNEVER apply a total circumferential dressing and wrap because this may compromise circulation and nerve function if constriction, from whatever cause, occurs.
TESTS OF WHITE BLOOD CELLS
White Blood Cell Count (WBC; Leukocyte Count)White blood cells (or leukocytes) are divided into two main groups: granulocytes and agranulocytes. The granulocytes receive their name from the distinctive granules that are present in the cytoplasm of neutrophils, basophils, and eosinophils. However, each of these cells also contains a multilobed nucleus, which accounts for their also being called polymorphonuclear leukocytes. In laboratory terminology, they are often called “polys” or PMNs. The nongranulocytes, which consist of the lymphocytes and monocytes, do not contain distinctive granules and have nonlobular nuclei that are not necessarily spherical. The term mononuclear leukocytes is applied to these cells.
The endocrine system is an important regulator of the number of leukocytes in the blood. Hormones affect the production of leukocytes in the blood-forming organs, their storage and release from the tissue, and their disintegration. A local inflammatory process exerts a definite chemical effect on the mobilization of leukocytes. The life span of leukocytes varies from 13 to 20 days, after which the cells are destroyed in the lymphatic system; many are excreted from the body in fecal matter.
Leukocytes fight infection and defend the body by a process called phagocytosis, in which the leukocytes actually encapsulate foreign organisms and destroy them. Leukocytes also produce, transport, and distribute antibodies as part of the immune response to a foreign substance (antigen).
The WBC serves as a useful guide to the severity of the disease process. Specific patterns of leukocyte response can be expected in various types of diseases as determined by the differential count (percentages of the different types of leukocytes). Leukocyte and differential counts, by themselves, are of little value as aids to diagnosis unless the results are related to the clinical condition of the patient—only then is a correct and useful interpretation possible. Signs and symptoms of increased WBCs include fever, bruising, petechiae, fatigue, anemia, bleeding of mucous membranes, weight loss, and history of infections.
Reference Values
Normal
Black adults: 3.2-10.0 × 103 cells/mm3 or × 109/L or 3200-10,000 cells/mm3
Adults: 4.5-10.5 × 103 cells/mm3 or × 109/L or 4500-10,500 cells/mm3
Children:
0-2 weeks: 9.0-30.0 × 103 cells/mm3 or × 109/L or 9000-30,000 cells/mm3
2-8 weeks: 5.0-21.0 × 103 cells/mm3 or × 109/L or 5000-21,000 cells/mm3
2 months-6 years: 5.0-19.0 × 103 cells/mm3 or × 109/L or 5000-19,000 cells/mm3
6-18 years: 4.8-10.8 × 103 cells/mm3 or × 109/L or 4800-10,800 cells/mm3
CLINICAL ALERT
WBC <500/mm3 or <0.5 × 103/mm3 (or × 109/L) is extremely dangerous and is often fatal.
WBC <2.0 × 109/L represents a critical value.
WBC >30,000/mm3 or >30.0 × 103/mm3 (or × 109/L) is a critical value.
NOTE
Different labs have slightly different reference values.
Procedure
Obtain a venous anticoagulated EDTA (lavender-topped tube) whole blood sample of 5 mL or a finger-stick sample. Place specimen in a biohazard bag.
Record the time when specimen was obtained (e.g., 7:00 a.m.).
Blood is processed either manually or automatically, using an electronic counting instrument such as the Coulter counter or Abbott Cell-Dyne.
Clinical Implications
Leukocytosis: WBC >11,000/mm3 or > 11.0 × 103/mm3 (or >11 × 109/L)
It is usually caused by an increase of only one type of leukocyte, and it is given the name of the type of cell that shows the main increase:
Neutrophilic leukocytosis or neutrophilia
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
