A blood panel is a test used to evaluate a patient's overall health and to screen for a wide variety of disorders. A blood panel is also known as a complete blood count (CBC), full blood count (FBC), or hemogram. A blood panel is often performed as part of a routine medical checkup or at the request of a physician seeking specific information.

No preparation is required for a blood panel. The health care provider will wrap an elastic band around the upper arm to stop the flow of blood and to make veins easier to find. The skin of the needle site is cleaned and the needle is inserted into the vein. A tube attached to the needle fills with blood, and the site is bandaged. The sample in the tube is then combined with an anticoagulant to prevent it from clotting before the blood panel can be performed.

A blood panel used to be performed by placing a slide of the blood sample under a microscope and manually counting cells; today the test is usually automated. The tube is placed on a rack on an automated analyzer. A small amount of the sample is removed via a small, narrow tube containing sensors that count the type and number of cells passing through it. The sensors usually either detect light or measure electrical impedance, and use characteristics such as size to determine which type of cells are present. This automated blood panel is very precise, so a manual count is performed only if there are indeterminate results caused by variables such as abnormal cells.

A blood panel includes both white and red blood cell counts. It also gives a white blood cell differential, a count of different white blood cell types that can give information about the immune system, such as identifying an allergic reaction. Red blood cell indices measure the amount and concentration of hemoglobin in the red blood cells, as well as their average size. A blood panel also includes a packed cell volume test, measuring the amount of space red blood cells take up in the blood. Platelets are counted to measure the body's ability to clot or control bleeding.

Aside from a routine medical exam, a blood panel may be performed for several reasons. Physicians order a blood panel for patients who have unexplained symptoms, such as excessive fatigue or weakness. A blood panel can help diagnose infections, or diseases of the blood such as leukemia. Physicians also use blood panels to check for any abnormal values, or excessive bleeding or clotting, prior to surgery. The blood panel is a commonly performed test because it provides a picture of overall health and can be used to diagnose or detect conditions that may require further treatment.