What is a Complete Blood Count (CBC) Blood Test?
A Complete Blood Count, or CBC blood test, is one of the most common blood tests that is usually ordered by a doctor. The goal of the complete blood count test is to determine the concentration of various cellular and intracellular components of the blood. Generally, the CBC blood test is carried out by highly specialized laboratory equipment that that analyzes the various components of blood within a few minutes. Most of the complete blood count consists of metrics concerning the red blood cells, white blood cells, and platelets found within the blood stream.
What Method is Used for the CBC Blood Test?
The CBC blood test involves obtaining a few milliliters of blood from the patient (one to three tablespoons’ worth). This can either be done directly, or be sectioned off from a previous sample of blood collected. The blood collection can be done in a variety of clinical settings, such as the doctor’s office, a phlebotomy laboratory, or a hospital.
When obtaining blood, the doctor, nurse, or phlebotomist will sterilize the patient’s skin with alcohol, then insert a needle into the cleansed area to obtain blood from one of the patient’s veins. The healthcare professional taking the blood will generally identify a vein that can be seen through the skin. If no vein can be seen, the healthcare professional will usually palpate the cleansed area to identify a vein that can be felt beneath the skin’s surface. After inserting the needle into the vein, the healthcare professional will use a syringe or vacuumed vial to collect the blood. The sample is then sent to a laboratory for analysis.
A Complete Blood Test
What does the CBC Blood Test Indicate, and What Does It Test For?
The CBC blood test examines the following:
- White Blood Cell Count (WBC) – this is the number of white blood cells found in a volume of blood. The normal range for this result is between 4,300 and 10,800 cells per cubic millimeter. This is also known as the leukocyte count.
- White Blood Cell Differential Count (WBC) – The white blood count is a composite of several different types of cells. The differential count will break down the number of granulocytes, lymphocytes, monocytes, eosinophils, and basophils that are present, and will present the prevalence of each type as a percentage.
- Red Blood Cell Count (RBC) – This is the number of red blood cells in a volume of blood. The normal range varies slightly depending on the equipment being used, but usually ranges between 4.2 to 5.9 million cells/cmm is considered average. This is sometimes called the erythrocyte count, and is expressed in SI units with a normal range of 4.2 to 5.9 x 1012 cells per liter.
- Hemoglobin (Hb or Hbn) – The count of hemoglobin found in a volume of blood. Hemoglobin is the protein found in red blood cells that allows the red blood to carry oxygen from the lungs to various body tissues, and also allows the transport of carbon dioxide created by cellular respiration to be carried away from tissues and exhaled. Hemoglobin also gives red blood cells their defining color. The normal range for men is 13 to 18 grams per deciliter, and for women is 12 to 16 grams per deciliter. In SI units, these translate to 8.1 to 11.2 millimoles/liter and 7.4 to 9.9 millimoles/liter respectively.
- Hematocrit (Hct) – This is the ratio of the volume of red blood cells relative to the volume of the blood as a whole. The normal range for this result depends on gender. For men, 45 to 52 percent is considered normal, and for women, 37 to 48 percent is considered normal. This is measured by spinning a blood sample in a centrifuge, which causes the red blood cells to pack at the bottom of the tube.
- Mean Corpuscular Volume (MCV) – this is the average amount of hemoglobin found in the average red blood cell. This is a calculated (not a tested) value, derived from the measurement of hemoglobin and the red blood cell count. Normal ranges are between 27 to 32 picograms.
- Mean Corpuscular Hemoglobin Concentration (MCHC) – this is an average of the concentration of hemoglobin in a given volume of red blood cells. This result is calculated from the hemoglobin measurement and the hematocrit. The normal range is between 32 and 36 percent.
- Red Cell Distribution Width (RDW) – measurement of the variability of red cell size and shape. High numbers indicate increased variation in size. The normal range is between 11 to 15.
- Platelet count – this measurement is a result of the number of platelets found in a volume of blood. These play a vital role in blood clotting. The normal range is between 150,000 and 400,000/cmm or 150 to 400 x 109/liter.
- Mean platelet volume: The average size of platelets in a volume of blood.
Complete Blood Count Examines
What is the CBC Blood Test Used For?
The CBC blood test is used to determine the likelihood of a variety of potential illnesses or chronic health problems that tend to might affect the various blood factors tested above. The CBC test can be used to detect illnesses such as infections, certain cancers, bone marrow problems, anemia, low blood oxygen levels, bleeding disorders, and severe inflammation. The CBC is also quite normal for a doctor to order alongside other tests, such as alongside a liver function panel, or as part of a normal checkup. The CBC test is relatively inexpensive, so it is often employed by healthcare providers as a cost-effective manner to determine if there are any underlying conditions that might avoid detection during a standard examination.
How is a CBC Blood Test Done?
A healthcare professional such as a doctor, nurse, or phlebotomist will cleanse a portion of the skin – usually on the arm, opposite of the elbow – with an alcohol wipe. This sterilizes the skin to prevent infection. They will then survey the area visually or by using their fingers to palpate the area in order to detect a vein. They will then insert a needle into the vein, and draw blood out with a syringe or vacuum test tube.