The complete blood count (CBC) is the most commonly prescribed blood test and is used to assess overall health and to diagnose or screen for a wide range of diseases and conditions, including infections, anemia, and blood cancers (leukemia, myeloma, and lymphoma).
A CBC is sometimes also called Full Blood Count / Panel or Blood Cell Count or Hemogram.
Depending on the reason this test was prescribed, if some results are outside the normal range your healthcare provider may or may not require further testing.
How is a CBC with diff performed?
A complete blood count is a very simple and quick test which does not require fasting or any other form of preparation (unless other tests are performed at the same time!). A nurse or technician will take a sample of your blood by inserting a small needle into a vein in your arm; blood is collected into a test tube and is then sent to the lab for analysis. The amount of blood drawn is very little and you can immediately resume any activity.
Why is a complete blood count prescribed?
There are several reasons why your doctor may have prescribed a CBC to you, including:
- As a routine check-up, to assess your overall health and as part of a yearly review of your health status.
- As part of a preventive screening, to gather information about the hematologic system.
- To diagnose a disease or condition, when you experience signs or symptoms that require medical testing to confirm a diagnosis or narrow down the possible causes.
- To monitor a known condition or disease and keep track of changes.
- To keep an eye on possible changes caused by a medical treatment you are undergoing, including chemo, medications, and surgeries.
What are the symptoms that may require a CBC test?
Among the signs and symptoms that may suggest the need for a complete blood count test are:
- Shortness of breath
- Signs of inflammation or infection, like swollen joints or lymph nodes
- Nausea or vomiting
What does a CBC with differential include?
Values included in a complete blood count with differential (CBC with diff) are the following:
- Red Blood Cell count (RBC) indicates the total number of red blood cells in the sample.
- Mean Corpuscular Volume (MCV) indicates the average size of RBC
- Mean Corpuscular Hemoglobin (MCH) indicates the average amount of hemoglobin in RBC
- Mean Corpuscular Hemoglobin Concentration (MCHC) indicates the concentration of hemoglobin in RBC
- Red Blood Cell Distribution Width (RDW) indicates how much RBC variate in size
- Hemoglobin (Hb or Hgb) measures the total amount of this protein found in the blood sample and which is found in RBC and is necessary to carry oxygen.
- Hematocrit (Hct) measures the concentration of RBC in the blood.
- Platelet count (PLT) measures the amount of these cell fragments that are fundamental in blood clotting.
- White Blood Cell count (WBC) indicates the total number of leukocytes (WBC) in the sample.
- Differential Count indicates the number of each of the 5 types of WBC, which are:
- Neutrophils, which are mainly involved in fighting bacteria by phagocytosis (ingestion and digestion).
- Lymphocytes, fight viruses and bacteria; can be B-cells which produce antibodies or T-cells which directly fight pathogens. Lymphocytes are responsible for our immune system memory which allows us to fight infections better the second time we encounter the same pathogen.
- Monocytes, which remove dead cells and kill pathogens through phagocytosis.
- Eosinophils, which are mainly involved in allergic reactions and fighting parasites.
- Basophils, which are involved in allergic and inflammatory responses.
Normal CBC Values and reference ranges and interpretation of abnormal results
The normal range of values varies slightly between different labs. This is because the reference values are established based on the average results from a large population. Factors like age, gender, ethnicity also influence reference ranges. A single value outside the “normal range”, especially if just slightly above or below it, does not necessarily mean something is wrong; results should be looked as a whole and interpreted based on the information known about the patient which is why it is always important to let a healthcare professional interpret and explain the results to you. Moreover, it is also important to check the same-subject variation of a blood test value (ie. Compare the result with previous results from the same patient) and not just the single result by itself.
In the sections here below where I indicate the possible meaning of higher or lower than normal values, I will only include some, but not all, of the possible reasons.
Normal RBC count range
Normal red blood cell count ranges are:
- 4.7-6.1 x 1012/L for adult males
- 4.2-5.4 x 1012/L for adult females
Meaning of abnormal RBC values
An RBC count greater than normal (erythrocytosis) may be caused physiologically by training or living at high altitudes. Among the many factors or conditions that may cause an abnormally high value there are chronic hypoxia and polycythemia vera.
A low RBC count (erythrocytopenia) may be caused physiologically by pregnancy. Among the many factors and conditions that may cause low red blood cell count results are blood loss, hemolysis, anemia and blood cancers.
Normal MCV range
Normal mean corpuscular volume ranges are:
- 80-95 fL for adults and children
Meaning of abnormal MCV values
High MCV may be caused by liver disease, folic acid (Vit. B9) deficiency and pernicious anemia (due to Vit B12 deficiency).
Low MCV may be caused by iron deficiency anemia or by thalassemia.
Normal MCH range
Normal mean corpuscular hemoglobin ranges are:
- 27-31 pg for adults and children
Meaning of abnormal MCH values
High MCH levels may be caused by macrocytic anemia.
Low MCH levels may be caused by microcytic anemia or hypochromic anemia.
Normal MCHC range
Normal mean corpuscular hemoglobin concentration ranges are:
- 32-36 g/dL for adults and children (or 32-36%)
Meaning of abnormal MCHC values
High MCHC levels may be caused by hemolysis or spherocytosis.
Low MCHC levels may be caused by iron deficiency anemia or thalassemia.
Normal RDW range
Normal red blood cell distribution width ranges are:
- 11-14.5% for adults
Meaning of abnormal RDW values
An increased RDW value may be caused by iron deficiency anemia, B6 or B12 deficiency anemia, or blood loss.
Normal Hemoglobin (Hb) range
Normal hemoglobin levels are:
- 14-18 g/dL or 8.7-11.2 mmol/L for adult males
- 12-16 g/dL or 7.4-9.9 mmol/L for adult females
Meaning of abnormal hemoglobin values
Increased hemoglobin levels may be caused physiologically by living or training at high altitudes or may be caused by dehydration, severe burns, heart disease, polycythemia vera.
Decreased hemoglobin levels may be caused physiologically by pregnancy, or may be caused by nutritional deficiencies, anemia, hemorrhage, hemolysis, lymphoma, splenomegaly, kidney disease.
Normal Hematocrit (Htc) range
Normal hematocrit levels are:
- 42-52% for adult males
- 37-47% for adult females
Meaning of abnormal hematocrit values
An increased hematocrit may be caused by severe dehydration, burns, erythrocytosis, polycythemia vera.
A decreased hematocrit may be caused by anemia, dietary deficiencies, bone marrow failure, kidney disease, lymphoma, leukemia, myeloma, hemorrhage, cirrhosis.
Normal platelet count range
Normal platelet levels are:
- 150-400 x 109/L for adults and children
Meaning of abnormal platelet values
Increased platelet levels (thrombocytosis) may be caused by iron-deficiency anemia, post-splenectomy syndrome, polycythemia vera and some malignant disorders.
Decreased platelet levels (thrombocytopenia) may be caused by chemotherapy, chronic or acute infections, hemorrhage, anemia, hereditary syndromes, hypersplenism.
Normal WBC count range
Normal white blood cell count levels are:
- 5-10 x 109/L for adults and children
Meaning of abnormal WBC values
Increased white blood cell count levels (leukocytosis) may be caused by trauma, stress, necrosis, inflammation, infections, or leukemia.
Decreased white blood cell count levels (leukopenia) may be caused by bone marrow failure, autoimmune diseases, drug toxicity, dietary deficiencies.
Normal Neutrophils count range
Normal neutrophils levels are:
- 55-70% or 2.5-8 x 109/L
Meaning of abnormal neutrophils values
Increased neutrophils levels (neutrophilia) may be a sign of an acute bacterial infection, stress, physical trauma, and leukemia.
Decreased neutrophils levels (neutropenia) may be a sign of dietary deficiencies, viral infections, aplastic anemia or be caused by chemotherapy and radiotherapy.
Normal Lymphocytes count range
Normal lymphocytes levels are:
- 20-40% or 1-4 x 109/L
Meaning of abnormal lymphocytes values
Increased lymphocytes levels (lymphocytosis) may be caused by viral or bacterial infections, leukemia, myeloma.
Decreased lymphocytes levels (lymphocytopenia) may be caused by sepsis, HIV, steroid therapy, radiation therapy, lupus, leukemia.
Normal Monocytes count range
Normal monocytes levels are:
- 2-8% or 0.1-0.7 x 109/L
Meaning of abnormal monocytes values
Increased monocytes levels (monocytosis) may be caused by chronic inflammation, viral infections, parasitic infections, tuberculosis.
Decreased monocytes levels (monocytopenia) may be caused by aplastic anemia, leukemia and medications such as prednisone.
Normal Eosinophils count range
Normal eosinophils levels are:
- 1-4% or 0.05-0.5 x 109/L
Meaning of abnormal eosinophils values
Increased eosinophils levels (eosinophilia) may be caused by allergic reactions, parasitic infections, autoimmune diseases, leukemia.
Decreased eosinophils levels (eosinopenia) may be caused by high levels of stress, use of steroids and Cushing’s syndrome.
Normal Basophils count range
Normal basophils levels are:
- 0.5-1% or 0.025-0.1 x 109/L
Meaning of abnormal basophils values
Increased basophils levels (basophilia) may be caused leukemia or myeloproliferative diseases.
Decreased basophils levels (basopenia) may be caused by stress or acute allergic reactions.
When should I call my doctor?
In case of dangerously low or high values, the labs immediately alert the family doctor and/or the emergency medical service.
To better understand values outside the normal ranges you can ask your healthcare provider to review the results of the CBC with you.
- Mosby’s Diagnostic and Laboratory Test Reference, 14th Edition
KD Pagana – Elsevier, 2019
- Understanding Blood Counts
Leukemia & Lymphoma Society
- Complete Blood Count (CBC)
MedlinePlus – US National Library of Medicine