Complete Blood Count (CBC)

A complete blood count (CBC) gives important information about the kinds and numbers of cells in the blood, especially red blood cells , white blood cells , and platelets. A CBC helps your health professional check any symptoms, such as weakness, fatigue, or bruising, you may have. A CBC also helps him or her diagnose conditions, such as anemia, infection, and many other disorders.

A CBC test usually includes:

• White blood cell (WBC, leukocyte) count. White blood cells protect the body against infection. If an infection develops, white blood cells attack and destroy the bacteria, virus, or other organism causing it. White blood cells are bigger than red blood cells but fewer in number. When a person has a bacterial infection, the number of white cells rises very quickly. The number of white blood cells is sometimes used to find an infection or to see how the body is dealing with cancer treatment.
• White blood cell types (WBC differential). The major types of white blood cells are neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Immature neutrophils, called band neutrophils, are also part of this test. Each type of cell plays a different role in protecting the body. The numbers of each one of these types of white blood cells give important information about the immune system. Too many or too few of the different types of white blood cells can help find an infection, an allergic or toxic reaction to medicines or chemicals, and many conditions, such as leukemia.
• Red blood cell (RBC) count. Red blood cells carry oxygen from the lungs to the rest of the body. They also carry carbon dioxide back to the lungs so it can be exhaled. If the RBC count is low (anemia), the body may not be getting the oxygen it needs. If the count is too high (a condition called polycythemia), there is a chance that the red blood cells will clump together and block tiny blood vessels (capillaries). This also makes it hard for your red blood cells to carry oxygen.
• Hematocrit (HCT, packed cell volume, PCV). This test measures the amount of space (volume) red blood cells take up in the blood. The value is given as a percentage of red blood cells in a volume of blood. For example, a hematocrit of 38 means that 38% of the blood's volume is made of red blood cells. Hematocrit and hemoglobin values are the two major tests that show if anemia or polycythemia is present.
• Hemoglobin (Hgb). The hemoglobin molecule fills up the red blood cells. It carries oxygen and gives the blood cell its red color. The hemoglobin test measures the amount of hemoglobin in blood and is a good measure of the blood's ability to carry oxygen throughout the body.
• Red blood cell indices. There are three red blood cell indices: mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). They are measured by a machine and their values come from other measurements in a CBC. The MCV shows the size of the red blood cells. The MCH value is the amount of hemoglobin in an average red blood cell. The MCHC measures the concentration of hemoglobin in an average red blood cell. These numbers help in the diagnosis of different types of anemia. Red cell distribution width (RDW) can also be measured which shows if the cells are all the same or different sizes or shapes.
• Platelet (thrombocyte) count. Platelets (thrombocytes) are the smallest type of blood cell. They are important in blood clotting. When bleeding occurs, the platelets swell, clump together, and form a sticky plug that helps stop the bleeding. If there are too few platelets, uncontrolled bleeding may be a problem. If there are too many platelets, there is a chance of a blood clot forming in a blood vessel. Also, platelets may be involved in hardening of the arteries (atherosclerosis).
• Mean platelet volume (MPV). Mean platelet volume measures the average amount (volume) of platelets. Mean platelet volume is used along with platelet count to diagnose some diseases. If the platelet count is normal, the mean platelet volume can still be too high or too low.

Why It Is Done

A complete blood count may be done to:

• Find the cause of symptoms such as fatigue, weakness, fever, bruising, or weight loss.
• Find anemia.
• See how much blood has been lost if there is bleeding.
• Diagnose polycythemia.
• Find an infection.
• Diagnose diseases of the blood, such as leukemia.
• Check how the body is dealing with some types of drug or radiation treatment.
• Check how abnormal bleeding is affecting the blood cells and counts.
• Screen for high and low values before a surgery.
• See if there are too many or too few of certain types of cells. This may help find other conditions, such as too many eosinophils may mean an allergy or asthma is present.

A complete blood count may be done as part of a regular physical examination. A blood count can give valuable information about the general state of your health.

C-Reactive Protein (CRP)

A C-reactive protein (CRP) test is a blood test that measures the amount of a protein called C-reactive protein in your blood. C-reactive protein measures general levels of inflammation in your body.

High levels of CRP are caused by infections and many long-term diseases. But a CRP test cannot show where the inflammation is located or what is causing it. Other tests are needed to find the cause and location of the inflammation.

Why It Is Done

A C-reactive protein (CRP) test is done to:

• Check for infection after surgery. CRP levels normally rise within 2 to 6 hours of surgery and then go down by the third day after surgery. If CRP levels stay elevated 3 days after surgery, an infection may be present.
• Identify and keep track of infections and diseases that cause inflammation, such as:
  • Cancer of the lymph nodes (lymphoma).
  • Diseases of the immune system, such as lupus.
  • Painful swelling of the blood vessels in the head and neck (giant cell arteritis).
  • Painful swelling of the tissues that line the joints (rheumatoid arthritis).
  • Swelling and bleeding of the intestines (inflammatory bowel disease).
  • Infection of a bone (osteomyelitis).
• Check to see how well treatment is working, such as treatment for cancer or for an infection. CRP levels go up quickly and then become normal quickly if you are responding to treatment measures.

A special type of CRP test, the high-sensitivity CRP test (hs-CRP), may be done to find out if you have an increased chance of having a sudden heart problem, such as a heart attack. Inflammation can damage the inner lining of the arteries and make having a heart attack more likely. However, the connection between high CRP levels and heart attack risk is not very well-understood.

Results

A C-reactive protein (CRP) test is a blood test that measures the amount of a protein called C-reactive protein in your blood.

Normal

Normal values may vary from lab to lab. Results are usually available within 24 hours.

C-reactive protein (CRP)

Normal:	0–1.0 mg/dL or less than 10 mg/L (SI units)

Any condition that results in sudden or severe inflammation may increase your CRP levels.

Some medicines may decrease your CRP levels.

High-sensitivity C-reactive protein (hs-CRP) levels

The hs-CRP test measures your risk for heart problems. It may be done to find out if you have an increased chance of having a sudden heart problem, such as a heart attack. However, the connection between high CRP levels and heart attack risk is not very well-understood.

High-sensitivity C-reactive protein (hs-CRP) levels

Less than 1.0 mg/dL	Lowest risk
1.0 to 3.0 mg/dL	Average risk
More than 3.0 mg/dL	Highest risk

Many conditions can change CRP levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and medical history.

What To Think About

• High-sensitivity C-reactive protein (hs-CRP) measures very low amounts of CRP in the blood. This test may help find your risk for heart problems, especially when it is considered along other risk factors such as cholesterol, age, blood pressure, and smoking. But the connection between high CRP levels and heart disease risk is not understood very well.
• High CRP levels before a major surgery may indicate that you are at risk for developing an infection after surgery.
• CRP testing can be used to see how well you respond to cancer treatment or treatment for an infection. Your CRP levels will rise quickly and then quickly return to normal if the treatment is working.
• High CRP levels may increase your chances of having other diseases, such as age-related macular degeneration and colon cancer.