Medically Reviewed by Dr. Rahul Gaikwad, MBBS, MD-General Medicine
The Complete Blood Count, commonly referred to as a CBC, is one of the most commonly ordered diagnostic tests in healthcare. It provides important information about your blood cells and can help your doctor assess your general health or diagnose a wide range of disorders, including infections, anemia, and other blood-related conditions. This article discusses what a CBC test is, its components, and how to interpret the results.
What Is a CBC Test?
A CBC test analyzes different components and aspects of your blood, such as red blood cells (RBCs), white blood cells (WBCs), platelets, haemoglobin, hematocrit, and other values. Blood is drawn from a vein, typically in your arm, and tested in a lab. The test is simple, non-invasive, and provides a lot of information regarding your health.
Components of a CBC Test
Red Blood Cells (RBCs)
RBCs are charged with transporting oxygen from your lungs to your body and bringing carbon dioxide back to the lungs in order to be exhaled. The most important measurements are:
RBC count: The amount of red blood cells in your blood.
Haemoglobin (Hgb): The red blood cell protein that oxygen is bound to.
Hematocrit (Hct): Percentage of your blood composed of red blood cells.
Mean Corpuscular Volume (MCV): The size of your red blood cells on average.
Mean Corpuscular Haemoglobin (MCH) and Mean Corpuscular Haemoglobin Concentration (MCHC): Measurements of the quantity and concentration of haemoglobin within your red cells.
Red Cell Distribution Width (RDW): Quantifies the red blood cell size variation.
White Blood Cells (WBCs)
WBCs belong to your immune system and work against infections.
WBC count: The total number of white blood cells.
WBC differential: Percentage of various types of white blood cells, such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
Platelets
Platelets are tiny cell fragments that are very important in the process of blood clotting. Important measurements include:
Platelet count: The amount of platelets in your blood.
Mean Platelet Volume (MPV): The size of your platelets on average.
Interpreting CBC Results
Interpreting CBC results involves comparing the values to reference ranges, which vary based on age, sex, and laboratory standards. Here’s what some common abnormalities might indicate:
Red Blood Cell Abnormalities
Low RBC, haemoglobin, or hematocrit: Can be a sign of anemia, blood loss, or deficiency in nutrients (e.g., iron, vitamin B12, or folate).
Increased RBC, haemoglobin, or hematocrit: May indicate dehydration, polycythemia Vera, or residence at high altitudes.
White Blood Cell Abnormalities
High white blood cell count (leukocytosis): Can signify infection, inflammation, stress, or leukaemia.
Low WBC (leucopoenia): May be an indicator of bone marrow disease, autoimmune disease, or viral infections.
Platelet Abnormalities
Low platelet count (thrombocytopenia): Can be caused by bone marrow diseases, some drugs, immune disorders or some mosquito-borne viral infections such as Dengue.
Increased platelet count (thrombocytosis): May be due to inflammation, iron deficiency, or myeloproliferative disorders.
When Is a CBC Test Ordered?
Physicians routinely recommend a CBC test during regular health checks or if a patient comes in with any of the following symptoms:
- Fever
- Cough
- Infectious disease
- Arthritis
- Weakness or fatigue
- Unexplained bruising or bleeding
- Chronic inflammation
The CBC test can also track chronic medical conditions, including anemia or blood disorders, and assess the success of treatments such as chemotherapy.
Preparing for a CBC Test
A CBC test typically does not need special preparation. But tell your doctor about any medications or supplements you are taking, as these may sometimes influence the results. The test is very quick, and results are usually available within a day.
Conclusion
The Complete Blood Count is a useful and broad-spectrum diagnostic test that yields valuable information regarding your health. By knowing its components and meaning, patients are able to value its role in diagnosing and treating medical illnesses. Always consult your healthcare provider about your CBC results to know what they mean for your own health condition.
References:
1. El Brihi J, Pathak S. Normal and Abnormal Complete Blood Count with Differential. [Updated 2024 Jun 8]. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK604207/
2. Complete blood test count, Cleveland Clinic, reviewed on 14 March 2024
3. Beverly George-Gay, Katherine Parker, Understanding the complete blood count with differential, Journal of Peri Anaesthesia Nursing, Volume 18, Issue 2, 2003, Pages 96-117, https://doi.org/10.1053/jpan.2003.50013
4. Kathy Doig, Bei Zhang, A Methodical Approach to Interpreting the Red Blood Cell Parameters of the Complete Blood Count, American Society for Clinical Laboratory Science Jul 2017, 30 (3) 173-185; Doi: 10.29074/ascls.30.3.173
5. Tefferi, Ayalew et al., How to Interpret and Pursue an Abnormal Complete Blood Cell Count in Adults Mayo Clinic Proceedings, Volume 80, Issue 7, 923 – 936
6. Understanding CBC Blood Counts, City of Hope, 12 June 2024
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