A CBC is a laboratory blood test. CBC stands for Complete Blood Count. It checks your blood for multiple things, including you white blood cell count (a marker of inflammation and/or infection), Hemoglobin and hematocrit levels (levels of your red blood cells), platelets (clotting components), etc.
Your lack of energy may be due to low red blood cells, which is also known as anemia
. Red blood cells carry oxygen in your blood to all of your organs. Since oxygen is required for production of energy in your body, it is important that enough red blood cells are available to carry enough oxygen to produce a sufficent amount of energy. Anemia can be caused by many things, including increased degradation, occult loss, decreased production, or anemia of chronic disease. Sometimes the causes is reversible. For example, sometimes anemias can be related to low intake of certain vitamins and foods.
A CBC is a good starting point in workup of lack of energy. It can show whether or not you are anemic and if so, which type of anemia you have. This may then further lead into more tests to work up the cause of the anemia and subsequently help to institute the appropriate treatment. Speak to your doctor
regarding the results and any further testing that he or she may want to perform.