Why is the CBC test done? &How do I prepare for this test? &How the test is performed?

 Complete blood count (CBC) (Part 2 )

Why is the CBC 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 the test is performed? 

 

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding; 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. 

For an infant or young child:

The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding

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:
• Vitamin B-12
• folate.
• Vitamin B6

What the risks are?  

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma ( blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

Special considerations   

• The RBC count may be decreased during pregnancy because of an increase in body fluids.
• The RBC will increase over a period of several weeks after moving to a higher altitude.
• Dehydration increases the RBC count.
• Drugs that can increase the RBC count include gentamicin and methyldopa. Drugs that can decrease the RBC count include chloramphenicol, hydantoins, and quinidine.
• Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

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.