CLINICAL LABORATORY TESTS
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Hematological Tests
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Blood contains 3 types of formed elements:
• RBCs
• WBCs
• Platelets
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Complete Blood Count
CBC includes:
1. Hemoglobin (Hb)
2. Hematocrit (Hct)
3. Total WBCs
4. Total RBCs
5. Mean Cell Volume (MCV)
6. Platelet Count
Clinical Lab Tests: Lecture-2
Mar 03, 2010
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Complete Blood Count
Depending on the lab, and order for a CBC
may or may not include:
1.Platelet Count
2.Reticulocyte Count
3.Leukocyte Differential Count
Clinical Lab Tests: Lecture-2
Mar 03, 2010
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RBCs (Erythrocytes)
The RBC count, which reports the no. of RBCs
found in a cubic mm (mm3) of whole blood,
provides as indirect estimate of the blood’s Hb
content.
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RBCs (Erythrocytes)
Normal values:
— 4.3 – 5.9 x 1012/L (4.3 – 5.9 x 106/mm3) for men
— 3.5 – 5.0 x 1012/L (3.5 – 5.0 x 106/mm3) for women
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RBCs (Erythrocytes)
RBCs are:
—
—
—
—
Produced in the bone marrow
Released into the peripheral blood
Circulate for approx. 120 days
Cleared by the reticuloendothelial system
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RBCs (Erythrocytes)
Function of RBCs is to transport oxygen to tissues
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RBCs (Erythrocytes)
The concentration of RBCs in the blood can be
measured to:
— Detect anemia
— Calculate Hct
— Calculate RBC indices
For monitoring quantitative changes in RBCs, the
Hct and Hb concentration generally are used.
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Hematocrit (Hct) or Packed Cell
Volume (PCV) or Erythrocyte Volume
Fraction (EVF)
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Hematocrit (Hct) or Packed Cell
Volume (PCV) or Erythrocyte Volume
Fraction (EVF)
The Hct is determined by centrifuging a capillary tube
of whole blood and comparing the height of the
settled RBCs to the height of the column of whole
blood.
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Hematocrit (Hct) or Packed Cell
Volume (PCV) or Erythrocyte Volume
Fraction (EVF)
— The percentage of red cells to the blood volume
is the Hct
— The Hct value is usually 3 times the Hb value
— The Hct value is given as a % or fraction of 1:
•
•
42% - 52% or 0.42 – 0.52
37% - 47% or 0.37 – 0.47
for men
for women
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Hematocrit (Hct) or Packed Cell
Volume (PCV) or Erythrocyte Volume
Fraction (EVF)
Low Hct Values
— Low Hct values indicate such conditions as anemia,
over hydration, or blood loss.
— It may also result from bone marrow suppressant
effects of drugs, chronic disease, genetic
alterations in RBC morphology (Sickle Cell Anemia)
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Hematocrit (Hct) or Packed Cell
Volume (PCV) or Erythrocyte Volume
Fraction (EVF)
High Hct Values
— High Hct values indicate such conditions as
polycythemia vera or dehydration
— In dengue fever – High Hct is a danger sign of
increased risk of dengue shock syndrome
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Hemoglobin
— Hb test measures the gram of Hb contained in 100 ml (1dL)
or 1 L of whole blood.
— It provides an estimate of oxygen carrying capacity of the
RBCs.
— The Hb value depends on the no. of RBCs and amount of
Hb in each RBC.
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Hemoglobin
Normal Values are:
— 14 – 18 g/dL for men
— 12 – 16 g/dL for women
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Hemoglobin
—Low Hb values indicate anemia
—A Hb determination is preferable to an RBC
determination because it directly reflects the
oxygen transport capability of blood
—However the Hct is most commonly used clinically
because it is technically simpler to perform
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RBC indices or Wintrobe indices
— Provide important information regarding RBC
size, Hb concentration & Hb weight
— Useful in the classification of anemia
— These indices include:
•
•
•
MCV
MCHb
MCHbC
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RBC indices or Wintrobe indices
— A peripheral blood smear can provide most of the
information obtained through RBC indices
— Observations of a smear may show variation in RBC shape
(poikilocytosis) e.g. sickle cell anemia or variation in RBC
size (anisocytosis) – mixed anemia (folic acid and iron
deficiency
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RBC indices or Wintrobe indices
Mean Cell Volume (MCV)
— It is the ratio of the Hct to the RBC count
— It assesses average RBC size and reflects any
anisocytosis
MCV = Hct% x 10 / RBC (millions)
Normal range for MCV is 90 ± 10
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RBC indices or Wintrobe indices
Mean Cell Volume (MCV)
— Low MCV indicates microcytic (undersize) RBC –
iron deficiency anemia
— High MCV indicates macrocytic (oversize) RBC –
Vitamin B12 or folic acid deficiency
— MCV can be normal in a patient with a ‘Mixed’
anemia
— RBC indices cannot take the place of direct
observation of a blood smear.
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RBC indices or Wintrobe indices
Mean Cell Hb (MCHb)
— It assesses the amount (wt.) of Hb in an average
cell.
MCHb = Hb x 10 / RBC (millions)
Normal range for MCHb is 30 ± 4
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RBC indices or Wintrobe indices
Mean Cell Hb Concentration (MCHbC)
— It represents the average concentration of Hb in
an average RBC, defined as:
MCHbC = Hb x 100 / Hct
Normal range for MCHbC is 34 ± 3
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RBC indices or Wintrobe indices
Mean Cell Hb Concentration (MCHbC)
— It is more reliable index of RBC Hb than the
MCHb
— In normochromic anemia, changes in the size of
RBCs are associated with corresponding
changes in the weight of Hb, but the
concentration of Hb remains normal
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RBC indices or Wintrobe indices
Mean Cell Hb Concentration (MCHbC)
— Low MCHbC indicates hypochromia (pale RBCs
due to decreased HB content) e.g. iron deficiency
anemia
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THE END
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