Primus Pathology Laboratory

Complete Blood Count (CBC) Test

Last Updated on July 28, 2022 by Dr. Neeraj Gujar


A complete blood count (or CBC) is a simple and common test that checks for any conditions that could affect your health. A CBC can diagnose a wide range of conditions from anemia to infection to cancer.

The CBC measures the changes in blood cell count and determines if they are increasing or decreasing. Your age and gender will affect the normal values. The normal range of values for your gender and age will be provided in your lab report.

A complete blood count tests several components and features of blood.

  • Red blood cells that are oxygen-carrying red blood cells
  • White blood cells that are used to fight infection
  • Platelets that are blood clotting aids
  • Haematocrit is the ratio of red blood cells to fluid components or plasma in your blood.
  • Haemoglobin is an oxygen-carrying protein found in red blood cells.

A complete blood count can reveal abnormal cell counts. This could indicate that there is an underlying medical condition.

Why CBC Test Is Done?

A CBC may be ordered by your doctor as part of a routine visit or if there are undiagnosed symptoms like bleeding or bruising. Your doctor can use a CBC to help with:

  • Assessing your overall health. A CBC is a basic test that doctors order to get a baseline picture of your health. Your doctor can also use a CBC to screen for potential health issues.
  • Diagnosing a medical problem. If you experience unexplained symptoms such as weakness, fatigue, fever, redness or swelling, bruising, or bleeding, your doctor may order a CBC.
  • Checking for a health issue. If you have been diagnosed as having a disorder that affects the blood cells, your doctor may order CBCs regularly to monitor your condition.
  • Keep an eye on your treatment. Regular CBCs may be required for certain medical treatments that can impact your blood cells. Based on your CBC, your doctor will be able to assess how effective your treatment is.

What is a CBC capable of detecting?

The CBC blood test can help your doctor diagnose a variety of conditions, diseases, and infections.

  • Anaemia is a condition in which there are not enough red blood cells to transport oxygen throughout the body.
  • Disorders like agranulocytosis, thalassemia, and sickle cell anemia.
  • Bone marrow disorders such as myelodysplastic syndromes.
  • Infections and other issues that lead to abnormally higher white blood cell or low white blood cell counts.
  • There are many types of cancer, such as Leukaemia or Lymphoma.
  • Vitamin and mineral deficiencies.
  • Side effects of chemotherapy, and some prescription drugs.

Also Read: How Do Doctors Use Iron Test to Diagnose Anemia or Hemochromatosis?

When To Get CBC Test Done?

You will need to get a complete blood test done if you experience symptoms like

  • Bleeding or bruising
  • Fever, nausea, and vomiting
  • Fatigue, weakness, or dizziness
  • Joint pain
  • Inflammation (irritation or swelling)
  • Problem with heart rate or blood pressure

How To Get CBC Tested?

A complete blood count test is done when the doctor prescribes it for diagnosing a health issue. Or you can do it as a part of your annual health checkup routine.

Before the Test

You can eat and drink as normal if your blood is being tested for a complete count. You may be asked to fast for certain periods if your blood sample is being used for other tests. You will be given specific instructions by your doctor.

During the Test

During a CBC, a trained technician will draw blood from a vein. This is usually from the inside of your elbow or the back of the hand. It will only take a few minutes.
The trained technician will:

  • Use an antiseptic wipe to clean your skin.
  • To help your veins expand, wrap an elastic band around your upper arm.
  • Insert a needle into a vein and collect blood samples in one or several vials.
  • Take off the elastic band.
  • Cover the area with a bandage to stop bleeding.
  • Label it and send your sample to a laboratory for analysis.

For Infants:

A nurse will usually sterilize the heel of the foot and use a small needle to prick the area. She/he will then gently squeeze the heel to collect some blood and place it in a vial.

After The Test

It can be uncomfortable to have your blood tested. You might feel a pinching or pricking sensation when the needle is inserted into your skin. Some people feel lightheaded or faint when they see blood. You may experience minor bruising but this will disappear in a few days.

It is important that you immediately contact your doctor if you experience any bleeding, infection, or other severe symptoms after your blood draw.

Test Results

The test results of blood cell counts will vary depending on your age, sex, and other health conditions. Here are the normal results for adults, but labs may have a slight variation in the results.

Blood componentNormal levels
RBC Blood TestIn men: 4.32-5.72 million cells/mcL
In women: 3.90-5.03 million cells/mcL
HaemoglobinIn men: 135-175 grams/L
In women: 120-155 grams/L
HaematocritIn men: 38.8-50.0 percent
In women: 34.9-44.5 percent
WBC Blood Test3,500 to 10,500 cells/mcL
Platelet count150,000 to 450,000/mcL

The CBC is not a diagnostic test. A wide range of conditions can be indicated by blood cell counts that are either too high or low. To diagnose a condition, special tests are required. Several conditions can cause abnormal CBC. Some additional testing may be required to understand the situation such as

  • Iron or other vitamins and minerals deficiencies
  • Heart disease
  • Bleeding disorders
  • Autoimmune disorders
  • Cancer
  • Problems with the bone marrow
  • Reaction to medication
  • Infection or inflammation

Your doctor may order another blood test if your CBC results are not normal. Your doctor may order additional tests to further assess your condition and confirm your diagnosis.


Interpreting Results

Blood samples collected in test tube

Any deviation in results may indicate a problem.

Red blood cell count, hemoglobin, and hematocrit. They are all related as they measure different aspects of your red blood cells.

Anemia is when these areas are lower than usual and can cause fatigue and weakness. Anaemia can be caused by low levels of vitamins or iron, as well as blood loss or underlying conditions.

An elevated red blood cell count (erythrocytosis) or high hemoglobin and hematocrit levels could indicate an underlying medical condition such as polycythemia or heart disease.

Low white blood cell count. This could be due to a medical condition such as an autoimmune disorder, bone marrow disease, or cancer. White blood cell counts can also be affected by certain medications.

If your white blood cell count is higher than normal, it could indicate an infection or inflammation. It could also indicate an immune disorder or bone marrow disease. A high white blood cell count could also indicate a reaction to the medication.

Platelet count. This could be an indication of an underlying medical condition or a side effect from the medication. You may need to have additional tests done to determine the reason for a lower platelet count than normal.

Talk to your doctor for more information about your results if your total blood count falls outside of the normal range.

What Else May CBC Test Tell?

To determine if you have a blood condition or illness, your doctor may order additional tests.

  • Mean corpuscular hemoglobin. (MCH): This is a test that determines how much hemoglobin you have in your red blood cells.
  • Mean corpuscular hemoglobin concentration (MCHC): This is the hemoglobin concentration in a given amount of blood.
  • Reticulocyte count: This test determines the number of red blood cell cells in your body.
  • Red blood cell distribution width (RDW): This indicates how many red blood cells you have.
  • Platelet distribution width (PDW): This indicates how large your platelets are.
  • Mean platelet volumes (MPV): This is the average platelet size in your blood.
  • White blood cells differential: There are five types of white blood cells – eosinophils, basophils, monocytes lymphocytes, and neutrophils. This test will show you how many of each type you have.

Final Takeaway

A complete blood count (CBC) test helps to measure the count of the cells that makes up your blood i.e., red blood cells, white blood cells, and platelets. So, it can be an overall indicator of your health problems. Your doctor can also suggest a test for diagnosing health issues.

You can either visit a diagnostic center for the test or check centers that can offer you CBC tests at home facilities.


Why Get Tested?

CBC test determines your general health as well as diagnoses, screen, or monitor a number of health disorders that can affect the blood cells.

  • Infections
  • Inflammation
  • Anemia
  • Bleeding Disorder
  • Cancer
When To Get Tested?

If your doctor suspects that you have a health condition causing deviation with blood cells or simply for diagnosing a health issue. It can also be tested as a part of an annual health checkup regime.

What diseases can a CBC detect?

Anemia, bone marrow disorders, autoimmune diseases, infections, dehydration, cancer, and nutritional deficiencies are some of the most common conditions that a CBC detects.

Is the CBC test done empty stomach?

There are no preparations required before a CBC. You may be asked to fast for certain periods if your blood sample is being used for other tests. You will be given specific instructions by your doctor.

Can a CBC detect heart problems?

CBC can be used to detect CHF (Congestive Heart Disease) because it can diagnose anemia, which has been known to cause CHF and produce similar symptoms to CHF. Your doctor may recommend a hs-CRP blood test to further diagnose the health issue.


by Dr. Neeraj Gujar

Dr. Neeraj Gujar has done his M.D. in Pathology from Government Medical College. He has worked at various organisations such as Breach Candy Hospital and Tata Memorial Hospital along with many other private organisations. During his working career, he realised the pressing need for exceptional quality diagnostic services. A diagnostic centre that can consistently give accurate results verified by a consultant doctor (M.D. Pathologist) on which your doctor can depend. This has been the founding principle of Primus Pathology and Diagnostics.

Leave a Reply

Your email address will not be published. Required fields are marked *