Hematology

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Chapter 45

• Hematology

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Introduction

• Hematology laboratory analyzes blood cells, their
  quantities, and their characteristics
• Hematology includes the study of hemostasis

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Formation of Blood Cells

• Blood is made of
• Plasma
• Erythrocytes (red blood cells)
• Leukocytes (white blood cells)
• Thrombocytes (platelets)
• Blood cells form in bone marrow
• Alternative sites include liver, spleen

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Checkpoint Question 1

• What is hematopoiesis and how is it influenced?

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Answer

• Hematopoiesis is the medical term for blood cell
  production. It is influenced by hormones and
  depends on adequate nutrients such as iron.

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Hematologic Testing

• Used to diagnose and manage disease of blood
  cells and of nonhematologic disease
• Common tests include
• Complete blood count (CBC)
• Erythrocyte sedimentation rate (ESR)
• Coagulation tests

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Complete Blood Count (CBC)

• Parameters
• White blood cell count and differential
• Red blood cell count
• Hemoglobin determination
• Hematocrit determination
• Mean cell volume
• Mean corpuscular hemoglobin
• Mean corpuscular hemoglobin concentration
• Platelet count

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Complete Blood Count (CBC) (continued)

• Dilution of whole blood is prepared
• Blood cells counted using a hematocytometer or
  hemocytometer

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White Blood Cell (WBC) Count

• Leukocytes provide main line of defense against
  foreign invaders
• Normal range is 4300 to 10,800/mm3

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WBC Count (continued)

• Leukopenia results from
• Chemical toxicity
• Nutritional deficiencies
• Chronic or overwhelming infections
• Certain malignancies

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WBC Count (continued)

• Leukocytosis results from
• Infections
• Inflammatory conditions
• Certain drugs
• Injuries to tissues
• Certain malignancies

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WBC Differential

• Performed to determine amounts of various WBC
  types present in peripheral blood
• Neutrophils
• Lymphocytes
• Monocytes
• Eosinophils
• Basophils

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Checkpoint Question 2

• What is leukopenia and what are four conditions
  that may cause it?

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Answer

• Leukopenia is diminished number of leukocytes. It
  can be caused by chemical toxicity, nutritional
  deficiencies, overwhelming or chronic infections,
  and certain malignancies.

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Neutrophils

• Defend against foreign invaders by phagocytizing
  them
• Normal percentage is 50 to 70
• Number increases with bacterial infections

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Checkpoint Question 3

• What is the function of neutrophils?

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Answer

• Neutrophils defend against foreign invaders by
  phagocytosis.

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Lymphocytes

• Recognize that a particle is foreign to the body
  and make antibodies specific to its destruction
• Normal percentage is 20 to 35
• Higher numbers signal a viral infection

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Monocytes

• Capable of phagocytizing foreign material
• Normal percentage is 3 to 5
• Monocytosis occurs with inflammatory responses
  and bacterial infections
• Monocytopenia occurs after administration of
  certain drugs or an overwhelming infection

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Eosinophils

• Function is not completely understood
• Normal percentage is 0 to 6
• Higher in allergic reactions and some infections

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Basophils

• Appear to be involved in allergic asthma, in
  contact allergies, and in hypothyroidism and
  chronic myeloid leukemia
• Represent less than 1 of circulating WBCs

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Checkpoint Question 4

• Elevated eosinophils and basophils are both seen
  with what condition?

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Answer

• Elevated eosinophils and basophils are both seen
  with allergic reactions.

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Red Blood Cell (RBC) Count

• Erythrocytes transport gases (mainly oxygen and
  carbon dioxide) between lungs and tissue
• Normal range
• For men, 4.6 to 6.2 million/mm3
• For women, 4.2 to 5.4 million/mm3

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Hemoglobin

• Functioning unit of the red blood cell
• Each hemoglobin molecule contains four protein
  chains called globins
• Each globin contains a heme unit with one iron
  molecule each

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Hemoglobin (continued)

• Millions of hemoglobin molecules in each RBC
• Normal range for men, 13 to 18 g/dL
• Normal range for women, 12 to 16 g/dL
• Anemia
• Detected with hemoglobin measurement

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Hematocrit

• Percentage of red blood cells contained in whole
  blood
• Purpose for measuring hematocrit is to detect
  anemia
• Normal range for men, 45 to 50
• Normal range for women, 37 to 48

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Checkpoint Question 5

• A patient has a hematocrit of 20. What does this
  percentage signify?

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Answer

• A hematocrit of 20 indicates that of the total
  blood volume, 20 of it consists of red blood
  cells.

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Mean Cell Volume

• Measures average size of red blood cells
• Used as an indicator for anemias
• Normal range is 80 to 95 fL
• Microcytosis commonly caused by iron deficiency
• Macrocytosis may be caused by deficiency of
  vitamin B12 or folic acid

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Mean Cell Hemoglobin and Mean Cell Hemoglobin
Concentration

• Indicate relative hemoglobin concentration in
  blood
• Normal range for MCG, 27 to 31 picograms
• Increase seen in macrocytic anemias
• Normal range for MCHC, 32 to 36 g/dL
• Reduced in true hypochromic anemia

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Platelet Count

• Essential to hemostasis
• Normal range is 200,000 to 400,000/mm3
• Thrombocytopenia caused by many conditions
• Treatment requires specific diagnosis of cause
• Thrombocytosis most often benign

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Erythrocyte Sedimentation Rate (ESR or SED Rate)

• Measures rate at which RBCs settle out in a tube
• Normal ranges
• For men, 0 to 10 mm/h
• For women, 0 to 20 mm/h
• Elevations not specific for any disorder

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Coagulation Tests

• Measure ability of whole blood to form a clot
• When vascular damage occurs, sequence of events
  occurs
• 1. Vasoconstriction
• 2. Platelet plug formation
• 3. Fibrin clot formation
• 4. Clot lysis and vascular repair

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Prothrombin Time (PT)

• Test in which calcium and thromboplastin are
  added to plasma then, clotting time is observed
• Normal range is 12 to 15 seconds
• Prolonged when a deficiency exists or due to
  coumarin therapy

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Partial Thromboplastin Time (PTT)

• Two-stage test in which partially activated
  thromboplastin is incubated with plasma, calcium
  is added, and clotting time is determined
• Normal range is 32 to 51
• May be prolonged in certain factor deficiencies

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Bleeding Time

• Performed to determine time required for blood to
  stop flowing from a very small wound
• Normal range is from 2 to 6 minutes

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Bleeding Time (continued)

• Prolonged times can occur from
• Decreased or impaired platelet function
• Use of medications
• Disease states
• Ingestion antiinflammatory medications

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Checkpoint Question 6

• What are the two most common tests used to
  determine how well a fibrin clot will form?

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Answer

• The two most common tests for determining how
  well a fibrin clot can form are prothrombin time
  and partial thromboplastin time.