Many times, people come into the medical office and request their medical record. Shortly after that, they return asking what in the world their lab results mean. The first question they ask is what in the world is a CBC? Most likely, they do this because the CBC is one of the highlighted tests most doctors prefer to use and then follow up through other tests. Before you have to ask your doctor’s office what a CBC is, here is what I tell patients.
Blood work is important for your doctor to determine what exactly is going on inside your body. If you are sick, typically your blood will give an insight into why you are ill. It rarely gives definitive answers, but it does narrow down the list of what is wrong.
What is a CBC typically used for?
A CBC is typically performed to detect anemia or infection. But it has many other uses. It is a mix of tests that when combined together can let your doctor know valuable information about what is going on inside your body. Here are the tests that are combined in a CBC.
Hematocrit: This test involves whole blood. It measures the percentage of red blood cells that are present in a given volume of blood. This test usually reveals if there is any type of anemia present.
Hemoglobin: Hemoglobin measures the amount of oxygen your cells are carrying. This measures the proteins that are actually able to carry the oxygen through the blood too.
Mean corpuscular hemoglobin (MCH): This test averages the amount of oxygen carrying hemoglobin inside of your red blood cells. Red blood cells that are too large will have a high MCH, and red blood cells that are too small will have a low MCH.
Mean corpuscular hemoglobin concentration (MCHC): This tells the average concentration of hemoglobin inside of your red blood cells. This test is used to check for anemia and other blood conditions, as well as hereditary and congenital disorders.
Mean Corpuscular Volume (MCV): This is the measurement of the size of your red blood cells. The size of your red blood cells is very important. If your red blood cells are larger than they should be, there could be a vitamin deficiency or anemia. When they are smaller than they should be, it could cause an iron deficiency anemia or a more serious condition.
Mean Platelet Volume (MPV) is done by machine. This machine tests the size, shape and number of platelets. This is important information since new platelets are larger than old ones. The physician is able to tell how long there has been an increase or decrease in platelets, giving him or her insight on what your bone marrow is producing.
Platelet count: This test is very important since platelets are the portion of the cell that allows your blood to clot. An increase or decrease in platelets can cause serious clotting issues, both inside and outside the body.
Red blood cell count (RBC): This is count of your red blood cells. Like the white blood cells, an increase or decrease can cause or be a side effect of illness.
Red blood cell distribution width (RDW): This test calculates the size differences in your red blood cells. This helps narrow down any problems with the blood and helps pinpoint the type of anemia a patient has.
White blood cell count (WBC): This test counts the number of white blood cells that are in your blood. Determining how many white blood cells are in a certain volume of blood allows the doctor to know whether you have high or low count.
White blood cell differential: This test looks at the types of white blood cells that are in your blood. There are five different types of white blood cells: neutrophils, lymphocytes, monocytes, eosionphils and basophils. Having the proper balance of the five is very important.
Why did my doctor order this test?
Many times, a doctor will order tests when you first start seeing them. This gives them a baseline reading, and what is typical for you. Since there is not a specific number that is normal, only “within normal limits,” this test is important to determine what is normal for you specifically.
If you become ill, your doctor may request another CBC to pinpoint any changes from your normal ranges and why you have become ill.
Your doctor may order the test again, even if you are not ill. This is because your doctor is focused on preventative care. Just because you do not have symptoms doesn’t mean that changes are not happening inside your body that could lead to illness. It is better to catch problems before they start.
How do I prepare for a CBC?
There is really nothing you need to do to get ready for a CBC. The only recommendation is that you do not work out for several hours after having the CBC done. This will ensure that your body has had time to properly seal the vein that was used to withdraw the blood.