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Is Fasting Required for CBC Blood Test?

Is Fasting Required for CBC Blood Test?

Many patients are often ordered a CBC blood test to help detect their overall health condition. These patients are often confused about fasting or not fasting before the test. This query will be addressed in the following health article and will also help solve most of your queries regarding this blood test.
Batul Nafisa Baxamusa
A regular visit to a doctor and you are asked to carry out a complete blood count (CBC) test. This blood test is often requested by doctors to make sure their patient's overall health is good. The CBC blood test is also known as full blood count (FBC) or a blood panel test. The test helps in screening many disorders like anemia, infections and even serious disorders like leukemia. This test screens disorders by calculations of the cellular components of the blood. These cellular components include the red blood cells, white blood cells as well platelets present in the blood. Most of the blood tests ordered like a blood glucose test or cholesterol test require one to fast for at least 12 hours. As CBC too is a blood test, it is quite natural and wise to ask if fasting is required.
What is CBC Blood Test?
Before going into the details of if fasting is necessary, it is important to understand what is a CBC blood test. As mentioned above, it is used to screen the blood components for presence of any underlying health conditions. The laboratory technician or a nurse will draw about few millimeters of your blood sample into a syringe. This blood sample taken will be analyzed for the following component measurements:
Red blood cell (RBC) count that will help analyze the actual number of red blood cell/volume of blood. It helps in finding out any increase or decrease in the RBC count.
Hemoglobin count helps in measuring the amount of proteins that help carry oxygen in the blood.
Mean corpuscular volume (MCV) that helps in measurement of the average size of the RBCs. If the count is elevated and RBCs are larger than normal, it indicates vitamin B12 deficiency. If the MCV count is decreased and the RBCs appear smaller than normal, it indicates iron deficiency, anemia or thalassemia.
Mean corpuscular hemoglobin (MVH) helps calculate the average amount of oxygen carrying hemoglobin inside the RBC.
Mean corpuscular hemoglobin concentration (MCHC) helps in calculation of the average concentration of hemoglobin present within a RBC.
Red cell distribution width (RDW) helps in calculation of the variation, if any, in the size of the RBCs. This variation is usually seen in cases of pernicious anemia.
White blood cell count (WBC) helps in calculation of the total number of WBC/volume of blood.
White blood cell differential helps in observation of the five different types of WBCs. These WBCs include the neutrophils, lymphocytes, monocytes, eosinophils and basophils. These blood cells are a part of the immune system and any changes within their count may indicate an underlying infection.
Platelet count helps in calculation of the number of platelets in a given volume of blood. Any increase or decrease will help indicate conditions that lead to excessive bleeding or clotting.
Why is CBC Blood Test Ordered?
CBC blood test is a common blood test that is ordered to check the overall health status of a patient. It is even ordered in case of inflammation, infection, unexplained bruising, bleeding, etc. Patients, who complain of weakness or fainting spells are also ordered the same. In some cases, it is ordered to check a medical condition or monitoring a medical treatment given to a patient.
Is Fasting for CBC Blood Test Necessary?
A complete blood count consists of the tests mentioned above. One can eat and drink normally before a test. Thus, the simple answer to 'is fasting required for CBC test', is No. Fasting is only required, if the doctor requests for a chemical panel test to be conducted along with complete blood count. Some of the tests in the chemical panel test like fasting glucose, fasting triglycerides, fasting lipids and glucose tolerance require a patient to fast. This means one needs to avoid drinking and eating any kind of food or drink for about 12 hours before the test. Diabetics who take insulin medications or injections too are asked to stop taking these medications for 12 hours. After the test is complete, they can immediately take their medications or injections. If you are wondering what foods to avoid before having a blood test that needs fasting, then the answer is avoid all foods. Fasting means no food and no drink. One can only have little amount of water. Thus, after your last meal of the day, one is asked not to eat or drink anything. The blood test, is thus, carried out early in the morning, to avoid any trouble to the patient.
You do not need to fast, if you are just getting your blood component analyzed. Until and unless, it is specified by your doctor to fast, you can eat and drink before the test. If you have any doubts, make sure you ask your doctor beforehand, if it is necessary to fast or not.
Disclaimer: This HealthHearty article is for informative purposes only. Speak to your healthcare provider for more details regarding the test and the requirements for the same.