Complete Blood Count Test (CBC)

Complete Blood Count Test (CBC)

Cell Counter

What is the complete blood count test (CBC)?

Many blood tests measure the amount of a particular chemical or protein in your blood, but a complete blood count checks the blood cells themselves. It measures the numbers of different types of blood cells, their sizes, and their appearance. It is a very common and useful blood test. Any irregularities can then be observed and used as a basis for follow-up check-ups.

 

In general, the test measures 3 main components of blood:

• Red blood cells (also called erythrocytes or RBCs). The test measures the number, size, shape, and appearance of the RBCs, and also the amount of hemoglobin in them. Hemoglobin carries oxygen from the lungs to the rest of the body. The part of the test called a hematocrit measures the percentage of your blood that is red blood cells.
•  Hematocrit Count
  The hematocrit count calculates the percentage of red blood cells per micro liter of blood. The range for an average male is from 42%-52% while the range for an average female would be from 37%-47%.
  This test is highly similar to the red blood cell count and has similar implications if the count is either too high or too low.
•   Hemoglobin Count
    Hemoglobin is found within the biconcave red blood cells and it combines readily with the oxygen molecule to form the unstable compound, oxy-hemoglobin. Blood with oxy-hemoglobin is observed to be bright red.
  The hemoglobin test should be coherent with the red blood cell and hematocrit test, otherwise, further testing may be needed to confirm the irregularities. Implications of the hemoglobin tests are in sync with that of the red blood cell count.
  The normal hemoglobin count is 12-16 grams of hemoglobin per deciliter of blood in females and 14-18 grams of hemoglobin per deciliter of blood in males.
• White blood cells (also called leukocytes or WBCs). The total count of white cells is measured. White blood cells help the body's immune system fight infection. When the amounts of each of the different types of white blood cells are also measured, the test is called a differential. The most common types are neutrophils (also called polymorph nuclear cells, PMNs, polys, or granulocytes) and lymphocytes.
• Platelets (also called thrombocytes). Platelets are not actually blood cells. They are fragments of large blood -forming cells. These fragments are essential for normal blood clotting.

•  Differential Blood Count

 As mentioned earlier in the site, there are five different types of white blood cells which serve different functions in our body. The five different types of white blood cells are the neutrophils, lymphocytes, monocytes, eosinophils and the  basophils.

The differential blood count is done to calculate the percentage of each type of white blood cell there is in relation to each other. It also gives a clearer picture in a diagnosis for the cause of a disease.

     In a normal person, there are:

• Neutrophils: 3150 to 6200
• Lymphocytes: 1500 to 3000
• Monocytes: 300 to 500
• Eosinophils: 50 to 250
• Basophils: 15 to 50

       Per micro liter of blood.
These counts are usually used as indicators to diseases/symptoms. A high        neutrophil count would suggest infection/cancer/physical stress. High lymphocytes counts are usually due to Acquire Immune Deficiency Syndrome (AIDS). High monocyte and eosinophil count usually points at bacterial infection.

Why is this test done? 

This test is usually done to see if:

• You have anemia (too few red blood cells).
• You have a high level of white blood cells (also called leukocytosis). A high white- blood -cell count is often a sign of infection.

This test may be done for other reasons as well, such as to:

• Look for the cause of anemia.
• Check for certain diseases.
• Check the number of platelets.

How do I prepare for this test?

• You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your health care provider knows about any medicines, herbs, or supplements that you are taking.
•  Don't stop any of your regular medicines without first consulting with your health care provider.

How is the test done? 

A small amount of blood is taken from your arm with a needle. The blood is collected in tubes coated with EDTA and sent to a lab. A machine in the lab measures the amounts of the different components in the sample of blood. The blood sample may also be viewed with a microscope to double check the different kinds of white blood cells.

Having this test will take just a few minutes of your time. There is no risk of getting AIDS, hepatitis, or any other blood -borne disease from this test. 

 What do the test results mean? 

            The normal ranges in most labs are:

• Red  blood cells (RBC): 4 to 6 million cells per micro liter
• White blood  cells (WBC): 5,000 to 10,000 cells per micro liter
• Hematocrit : for women, 36% to 45%; for men 41% to 47%
• Hemoglobin : for women, 12 to 15 grams per deciliter; for men, 14 to 16 grams per deciliter
• Platelets: 150,000 to 450,000 per micro liter.

These ranges may vary from lab to lab. Normal ranges are usually shown next to your results in the lab report.

Some of the reasons your red blood cell count may be higher than normal are:

• You haven't had enough fluids.
• You are a smoker.
• You have polycythemia Vera, a disease that causes your blood to be too thick because you're making too many red blood cells.
• You have smoker's lung disease.

A red blood cell count or hemoglobin level lower than normal is called anemia. The size of the red blood cells gives an important clue to possible causes of anemia:

• Anemia with small red  blood cells (called microcytic anemia) may be caused by:
• a lack of iron
• Bleeding, such as from a stomach ulcer.
• Anemia with large red blood  cells (called macrocytic anemia) may be caused by a lack of the vitamins:
• B-12
• folate.

Some of the reasons your white blood cell count may be higher than normal are:

• You have an infection.
• You have inflammation.
• You are taking certain medicines, such as prednisone.
• You have a type of cancer called leukemia.

Your white blood cell count may be lower than normal if you have a viral infection, including the common cold.

Your platelet count may be higher than normal if you have an autoimmune disease, such as rheumatoid arthritis or Crohn's disease.

Some of the reasons your platelet count may be lower than normal are:

• You are taking certain medicines, such as sulfa drugs, quinine, or heparin.
• You have sepsis (blood infection) or another serious illness.
• You have an autoimmune disease, such as lupus.

White Blood Cell Count (WBC) and Differential

White blood cells, or leukocytes, are classified into two main groups: granulocytes and nongranulocytes (also known as granulocytes).

• The granulocytes, which include neutrophils, eosinophils, and basophiles, have granules in their cell cytoplasm. Neutrophils, eosinophils, and basophiles also have a multilobed nucleus. As a result they are also called polymorphonuclear leukocytes or "polys." The nuclei of neutrophils also appear to be segmented, so they may also be called segmented neutrophils or "segs."
• The nongranuloctye white  blood cells, lymphocytes and monocytes, do not have granules and have nonlobular nuclei. They are sometimes referred to as mononuclear leukocytes.

The lifespan of white blood cells ranges from 13 to 20 days, after which time they are destroyed in the lymphatic system. When immature WBCs are first released from the bone marrow into the peripheral blood, they are called "bands" or "stabs." Leukocytes fight infection through a process known as phagocytosis. During phagocytosis, the leukocytes surround and destroy foreign organisms. White blood cells also produce, transport, and distribute antibodies as part of the body's immune response.

Two measurements of white blood cells are commonly done in a CBC:

• the total number of white blood cells in a microliter (1x10^-9 liters) of blood, reported as an absolute number of "X" thousands of white blood cells, and
• the percentage of each of the five types of white blood cells. This test is known as a differential or "diff" and is reported in percentages.

Normal values for total WBC and differential in adult males and females are:

• Total WBC: 4,500 - 10,000
• Bands or stabs: 3 - 5 %
• Granulocytes (or polymorphonuclears)
• Neutrophils (or segs): 50 - 70% relative value (2500-7000 absolute value)
• Eosinophils: 1 - 3% relative value (100-300 absolute value)
• Basophils: 0.4% - 1% relative value (40-100 absolute value)
• Agranulocytes (or mononuclears)
• Lymphocytes: 25 - 35% relative value (1700-3500 absolute value)
• Moncytes: 4 - 6% relative value (200-600 absolute value)

Each differential always adds up to 100%. To make an accurate assessment, consider both relative and absolute values. For example a relative value of 70% neutrophils may seem within normal limits; however, if the total WBC is 20,000, the absolute value (70% x 20,000) would be an abnormally high count of 14,000.