Do You Need to Fast Before a CBC Blood Test?

Individuals do not need to fast before a CBC, or complete blood count, test, states The test can be done at any time, and the patient does not have to do anything to prepare for the test.

CBC blood tests are often a part of a routine health check. Doctors also use them to help determine if the patient has an infection or to check levels of certain medications in the blood, states Cleveland Clinic. Doctors can use the results of the CBC to help diagnose conditions such as cancer, autoimmune diseases, anemia, vitamin deficiencies and bone marrow conditions.

The CBC blood test measures the levels of the components in the blood, including red blood cells, white blood cells, platelets and hemoglobin, according to Cleveland Clinic. It also measures the size and concentration of red blood cells.