All you need to know about taking a CBC or Complete Blood Count test

CBC, an acronym for Complete Blood Count, is a common blood test most doctors will prescribe in order to gauge if you suffer from any kind of infection, are anemic, or to simply know if there is anything in your body that is causing your symptoms. While it is not a conclusive test, it is widely used to understand how well you are generally. That being said, understanding what all the medical jargon in your report means can be tough. So in order to help you out, here is everything you need to know about your CBC reports.

What does a CBC test involve?

A technician will tie a band around your arm so that the veins on that hand are more prominent. The site is cleaned with an alcohol swab. A fresh, sealed disposable syringe is prepared, the vein is punctured with the syringe and the blood withdrawn.

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After the procedure, you will be given a cotton swab to place on the place where the injection pricked you and will be asked apply pressure to the area in order to stop the bleeding. In some cases you might notice a bruise in the place where the needle entered your skin, this is normal and should fade away in a few days.

A word of caution: Do tell your doctor and the lab technician before the you undergo the test if you suffer from a bleeding or clotting disorder or are taking medicines like aspirin, warfarin or other blood-thinning agents, as in such cases the bleeding might take a while to stop.

Why would my doctor order a CBC test?

Some of the common reasons for prescribing this tests are:

  • If you experience fatigue, weight loss, fever, bruising etc.
  • If you suffer from abnormal amounts of bleeding. For instance if you are bleeding much more than normal during your periods.
  • If your doctor suspects you are suffering from an infection.
  • In case your doctor suspects you could be suffering from certain blood related cancers like leukemia.
  • Diagnose certain conditions like asthma and allergies.
  • If you are scheduled for a surgery.
  • In case you suffer from cancer and are undergoing radiation and chemotherapy. This is done to check if and how the therapy is affecting on your blood cells.

What do each of the parameters mean?

A CBC has a number of fields that indicate one factor tested in your blood. The aspects tested are as follows:

Red blood cell (RBC) count

Normal range: 4.5 to 5.5 million cells/cubic mm

Why is it important?

Since RBCs are essential to carry oxygen to different parts of the body, low levels of this blood cell means decreased oxygen supply to the body leading to fatigue and weakness or anaemia. Low levels of RBCs are seen in iron deficiency anemia, thalassemia, stomach ulcers, sickle cell anemia and certain cancers.

If the levels of RBCs are higher than normal, they stick to each other, form clumps and block blood vessels. High levels are seen in case of chronic smokers, alcoholics, people with long-term lung, kidney, heart or liver disease. It may also be increased in cases of dehydration, burns, diarrhoea and vomiting.

White blood cell (WBC) count

Normal range: 4000 11000 cells/ cu mm. A value above 11000 is termed as leucocytosis and a value less than 4000 is termed as leucopenia.

White blood cells are a group of 5 cells that help to protect your body from infection. Here are the normal range of each of those components:


Why is it important?

When your WBC counts are high, the first aim is to rule out an infection as the cause. Sometimes a very high count could indicate leukemia, while a slightly elevated count can also be seen in pregnancy or in children below the age of 2 years, which is absolutely normal. When it comes to what elevated levels of each of the components indicates, here's what you should know:

  • If the percentage of neutrophils shows an increase, it could indicate a bacterial infections.
  • Elevated levels of lymphocytes could indicate a viral infection.
  • Increased levels of eosinophils could be an indicator of allergies or parasitic infection.

On the other hand low levels of WBCs are commonly seen in people who are either being treated with medications that contain steroids, are undergoing treatment for cancer or could indicate a malfunctioning of the bone marrow.

Platelet count:

Normal range: 1.5 to 4 lakhs/cu mm

Why is it important?

Platelets are the tiny cells in your blood that help in the formation of blood clots. This count is especially important to determine if you might be suffering from malaria or dengue. This count is especially important in the case of dengue, as an extremely low level of platelets in the body could lead to hemorrhaging and bleeding into the brain.


Normal range: Normal haemoglobin count in a male is 13-15 gms/ dl. In a healthy female it is 12 14 gms/ dl.

Why is it important?

Haemoglobin is the substance in your red blood cells that carries oxygen. A value less than 12 gms/ dl is indicates anemia, which could be either be due to deficiency of iron, vitamin B12 or folic acid. Deficiency of these could be due to a diet deficient in these nutrients, blood loss in your body or your body is unable to absorb these even though you are are taking it in adequate quantities.

Apart from that a low haemoglobin count could also be an indicator of a chronic disease. Low haemoglobin would result in the person complaining of tiredness, swelling of legs, strange desire to eat chalk or cement (pica) especially if you have iron deficiency anemia and sometimes even tingling and numbness in legs in case of Vitamin B12 or folic acid deficiency which is called as megaloblastic anemia.

Peripheral smear:

Sometimes, your doctor could also ask for a peripheral smear. In this a drop of blood is taken on a glass slide, spread and stained to see the RBCs, WBCs and platelets. This test helps to look for the presence of parasite in cases of malaria or filaria. Also, if you suffer from anemia, the smear will also gives information about the type of anemia you might be suffering from.

ESR (erythrocyte sedimentation rate):

Normal range: Normal values are 2-6 mm at the end of one hour.

High values may be seen in infections. Very high values if reported might indicate tuberculosis or multiple myeloma (a form of cancer of the bone marrow).

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