Red blood cell RBC count. Hemoglobin Hgb. Red blood cell indices. Platelet thrombocyte count. Mean platelet volume MPV. There are many other reasons that a doctor may want this blood test, including to: Find the cause of symptoms such as fatigue, weakness, fever, bruising, or weight loss.
Check for anemia. See how much blood has been lost if there is bleeding. Diagnose polycythemia. Check for 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.
For instance, too many eosinophils may be a sign of an allergy or asthma. A blood count can give valuable information about the general state of your health.
How To Prepare In general, there's nothing you have to do before this test, unless your doctor tells you to. How It Is Done A health professional uses a needle to take a blood sample, usually from the arm. How It Feels When a blood sample is taken, you may feel nothing at all from the needle. Risks There is very little chance of having a problem from this test.
Results Normal Each lab has a different range for what's normal. Blood smear results Normal: Blood cells are normal in shape, size, color, and number. High values Red blood cells RBC. Conditions that cause high RBC values include smoking, exposure to carbon monoxide, long-term lung disease, kidney disease, some cancers, certain forms of heart disease, alcohol use disorder , liver disease, a rare disorder of the bone marrow polycythemia vera , and a rare disorder of hemoglobin that binds oxygen tightly.
Conditions that affect the body's water content can also cause high RBC values. These conditions include dehydration , diarrhea or vomiting, excessive sweating, and the use of diuretics. The lack of fluid in the body makes the RBC volume look high. This is sometimes called spurious polycythemia. White blood cells WBC, leukocytes. Conditions that cause high WBC values include infection, inflammation, damage to body tissues such as a heart attack , severe physical or emotional stress such as a fever, injury, or surgery , kidney failure, lupus , tuberculosis TB , rheumatoid arthritis , malnutrition, leukemia , and diseases such as cancer.
The use of corticosteroids , underactive adrenal glands , thyroid gland problems, certain medicines, and removal of the spleen can also cause high WBC values. High platelet values may be seen with bleeding, iron deficiency, some diseases like cancer, or problems with the bone marrow. Low values Red blood cells RBC. Anemia lowers RBC values. Anemia can be caused by heavy menstrual bleeding, stomach ulcers , colon cancer , inflammatory bowel disease , some tumors, Addison's disease , thalassemia , lead poisoning , sickle cell disease , and reactions to some chemicals and medicines.
A low RBC value may also be seen if the spleen has been taken out. A lack of folic acid or vitamin B12 can also cause anemia, such as pernicious anemia. This is a problem with absorbing vitamin B The RBC indices value and a blood smear may help find the cause of anemia. To do that, a health professional will:. It's best to try to relax and stay still during the procedure because tensing muscles can make it harder and more painful to draw blood.
And if you don't want to watch the needle being inserted or see the blood collecting, you don't have to. Look the other way and maybe relax by focusing on saying the alphabet backward, doing some breathing exercises, thinking of a place that makes you happy, or listening to your favorite music.
Most blood tests take just a few minutes. Occasionally, it can be hard to find a vein, so the health professional may need to try more than once. The health professional will remove the elastic band and the needle and cover the area with cotton or a bandage to stop the bleeding. Afterward, there may be some mild bruising, which should go away in a few days. Blood samples are processed by a machine, and it may take a few hours to a day for the results to be available.
If the test results show signs of a problem, the doctor might order other tests to figure out what the problem is and how to treat it. A CBC is a safe procedure with minimal risks. Some people might feel faint or lightheaded from the test.
Visit The Symptom Checker. Read More. Blood Test: Lipid Panel. Pelvic Ultrasound. Rapid Strep Test. Abdominal Ultrasound. CT Head Scan. Other reasons your doctor may order a CBC can include: If you are ill and have a fever or if he or she suspects any kind of infection.
If you are tired or are losing weight without trying. If you have any sign of cancer, including general weakness, bruising, or bleeding. Things to consider Having CBC lab work done poses very little risk to your health. These are some of the health problems that can be identified by a CBC: anemia low iron autoimmune disorders bone marrow problems cancer dehydration heart disease infection inflammation vitamin and mineral deficiencies Questions to ask your doctor When will I get my test results back from the lab?
Will you notify me of my test results even if they are normal? Why are you ordering this test? Could the medicines I am taking affect my test results? Should I fast before the test? Resources U. Last Updated: September 8, This article was contributed by familydoctor. Categories: Tests and Procedures. Tags: blood tests , red blood cells.
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