Complete Blood Count (CBC)
last authored: Nov 2009, David LaPierre
last reviewed:
Introduction
The CBC is one of the most basic means of determining various basic parameters of whole blood, and is assessued using automated machines. Hemoglobin, RBC count, and MCV are measured, while MCH, MCHC, RDW, and hematocrit are calculated.
Ranges are given for 95% of the population. This means 5% of normal people will have 'suspicious' parameters.
Normal CBC values
hematocrit red blood cell count hemoglobin MCV MCH MCHC RDW retic. count platelet count WBC count
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0.42 - 0.54 5.4 +/- 0.7 (x1012/L) 14-18 g/dl 80-95 fl 27-33 pg 330-360 g/L
0.5-1.5% 150-400 x 103 / µl 4.5-11.0 x 109/L or 5000-10,000 /µl |
0.38 - 0.47 4.8 +/- 0.6 12-16 g/dl 80-100 fl
0.5-1.5% 150-400 x 103 / µl |
note: mm3 = µl 103/µl = 106/L
Hemoglobin and hematocrit change over life.
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RBCs contain a mixture of Hb, oxyhemoglobin (HbO2) carboxyhemoglobin (HbCO), and methemoglobin (Hi). It is important to measure a stable derivative to ensure accurate readings.
Most people use the cyanmethemoglobin (HiCN) method:
- blood is diluted in solution of potassium terricyanide and potassium cyanide
- hemoglobin is oxidized to hemiglobin (Hi; methemoglobin)
- KCN ionizes to form CN-, which forms HiCN
- absorbance is measured at 540 nm and compared with a standard
other forms are also measured - Hb, Nb02, Hi
Hematocrit (Hct) is the portion of blood occupied by RBCs. It is expressed as a percentage or decimal fraction.
It may be measured directly, by centrifgation, or indirectly, by multiplying x x
Red Blood Cell Count can be done by hemocytometer, but no longer.
RBC volume, or mean corpuscular volume (MCV), measures the average size of the blood cell, is perhaps the most important measurement in the CBC.
It is directly measured by the instrument (mean height of the voltage pulses - Coulter principle)
expressed in femtolitres (um3)
Increases and decreases in macrocytic and microcytic anemias, respectively.
can be estimated by comparing size to lymphocyte nucleus size.
Red Cell Distribution Width (RDW) is the coefficient of variation of RBC size distribution.
It is expressed as a percentage.
It measures anisocytosis (abnormal variation in RBC size)
Mean Corpuscular Hemoglobin (MCH) is the weight content of the average red cell. It provides similar information as the MCV. Red blood cells with a low MCH are described as hypochromic.
The normal red blood cell contains approximately 32 pg of Hb, which increases and decreases in macrocytic and microcytic anemias, respectively.
Mean Corpuscular Hemoglobin Concentration (MCHC) is the average concentration of hemoglobin in a given volume.
MCHC = Hb/ Hct
Reticulocyte count assesses the bone marrow response to anemia.
RNA can be visualized using supravital staining, which appears as polychromasia
Can be reported as % reticuocytes, absolute number, or reticulocyte index.
Normal adult range is 0.5-1.5%
Platelet Count
White blood cell count and differential can be 3 part or 5 part.
lymphocytes
- T cells: 70-80%; CD4:CD8 = 2:1 ratio
- B cells: 10-20%
- NK cells: 5-10%
neutrophils: 40-80% bands: 0-5%
lymphocytes: 20-40% monocytes: 2-10%
eosinophils: 0-7% basophils: 0-1.5%
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