Why is cbc done

A CBC measures the following: total number of red blood cells the RBC count total amount of hemoglobin in the blood percentage of blood made up of red blood cells the hematocrit average red blood cell size the mean corpuscular volume average weight of hemoglobin per red blood cell the mean corpuscular hemoglobin average amount of hemoglobin per red blood cell the mean corpuscular hemoglobin concentration total number of white blood cells number of each type of white blood cell the WBC differential , including neutrophils the absolute neutrophil count, or ANC number of platelets the platelet count.

A CBC is a common blood test. It is often done as part of a routine checkup, but can be done at any time. A CBC may be done to: learn information about your general health check how well the bone marrow and spleen are working help diagnose diseases and conditions that affect blood cells, such as anemia , infection, blood disorders or leukemia provide a baseline to compare with future CBCs check for bone marrow suppression monitor a condition as a part of follow-up.

You may be given special instructions to follow before having a CBC done. Check with the lab to see if you should avoid any medicines and for how long. Blood is usually taken from a vein in the arm.

An elastic band tourniquet is wrapped around your upper arm to apply pressure to the area and make the veins easier to see. You may be asked to make a fist so the veins stand out more. The skin is cleaned and disinfected. A needle is inserted into the vein and a small amount of blood is removed. You may feel a prick or stinging sensation. The blood is collected in a tube and labelled with your name and other identifying information.

Sometimes more than one tube of blood is collected. The tourniquet is removed and the needle is withdrawn. You may feel mild discomfort when the needle is withdrawn. Pressure is applied to the area where the needle was inserted until bleeding stops. A small bandage may be put on the area. The blood collected is examined by a specialist in the lab a lab technologist using microscopes and other special equipment.

A CBC does not usually cause any side effects. If side effects happen, they are usually minor and happen at the needle site. Side effects that may happen include: discomfort bleeding bruising swelling infection. CBC results are given as numbers and often depend on certain factors including sex, age and medical history.

They should be compared to a normal reference range or to previous results to have meaning. Normal ranges for CBCs may vary slightly from lab to lab. A CBC usually provides general information that can give doctors clues to possible health problems. Information from a CBC helps doctors decide whether other tests or procedures are needed to make a diagnosis. The information may also help your doctor develop or revise treatment plans.

A doctor familiar with your medical history and overall health is the best person to explain your CBC results and what they mean for you. Common terms used to describe CBC results are: anemia — not having enough healthy RBCs or hemoglobin leukopenia — a low number of WBCs neutropenia — a low number of neutrophils leukocytosis — an increased number of WBCs thrombocytopenia — a low number of platelets thrombocytosis — an increased number of platelets.

CBC results can be low or high for many reasons. Some examples of abnormal CBC results related to cancer are listed below. A low RBC count may be due to: anemia due to prolonged bleeding or blood loss hemorrhage , a diet lacking iron or certain vitamins, certain types of chemotherapy, blood disorders or chronic disease Hodgkin lymphoma and other lymphomas cancers of the blood, such as leukemia and multiple myeloma some myeloproliferative disorders. Results in the following areas above or below the normal ranges on a complete blood count may indicate a problem.

Red blood cell count, hemoglobin and hematocrit. The results of your red blood cell count, hemoglobin and hematocrit are related because they each measure aspects of your red blood cells. If the measures in these three areas are lower than normal, you have anemia.

Anemia causes fatigue and weakness. Anemia has many causes, including low levels of certain vitamins or iron, blood loss, or an underlying condition. A red blood cell count that's higher than normal erythrocytosis , or high hemoglobin or hematocrit levels, could point to an underlying medical condition, such as polycythemia vera or heart disease.

White blood cell count. A low white blood cell count leukopenia may be caused by a medical condition, such as an autoimmune disorder that destroys white blood cells, bone marrow problems or cancer.

Certain medications also can cause white blood cell counts to drop. If your white blood cell count is higher than normal, you may have an infection or inflammation. Or, it could indicate that you have an immune system disorder or a bone marrow disease.

A high white blood cell count can also be a reaction to medication. For specifics about what your complete blood count results mean if they fall outside the normal ranges, talk to your doctor. Mayo Clinic does not endorse companies or products. The test results will provide your doctor with a count of how many blood cells there are, and also describe their shape, size, and content. The results of a CBC can reveal a number of health conditions to your doctor, from anemia and some types of cancer to vitamin and mineral deficiencies.

If you have a condition that requires you to take daily medication, your doctor may order a CBC regularly to make sure your blood counts remain consistent. You are not required to fast not eat solid foods for 12 hours or so , unless you are having other tests done at the same time that require it. However, you may want to wear a short-sleeved shirt or one that easily rolls up to expose the lower half of your arm. You will most likely have to visit a lab to have the test done. At the lab, a phlebotomist a person trained to draw blood for medical testing will use a needle to collect a vial sometimes more than one of blood.

The blood is most often collected from a vein on the inside of your elbow or on the back of your hand. The CBC test takes only a few minutes. The results are usually available to your doctor by the following day.

In emergency situations, CBC results can be reported in an hour. The report will include the number of red blood cells and white blood cells.

Red blood cells are important because they carry oxygen throughout your body. A low red blood cell count could mean that you have anemia. White blood cells are warriors that fight infections. A high white blood cell count could mean that you have an infection. Blood count is also affected by altitude. The higher up you are, the more oxygen you need red blood cells.

Following the CBC, your doctor will evaluate the results. If your blood count is normal, you will not need to do anything.