Complete Blood Count (CBC)

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  • Also Known As:
  • CBC
  • Hemogram
  • CBC with Differential (CBC with diff)
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Where Lab Tests Are Performed

At a Glance

Why Get Tested?

To determine your general health status; to screen for, diagnose, or monitor any one of a variety of diseases and conditions that affect blood cells, such as anemia, infection, inflammation, bleeding disorder or cancer

When To Get Tested?

As part of a routine medical exam; when you have signs and symptoms that may be related to a condition that affects blood cells; at regular intervals to monitor treatment or disease status or when you are receiving treatment known to affect blood cells

Sample Required?

A blood sample drawn from a vein in your arm or a fingerstick or heelstick (newborns)

Test Preparation Needed?

None

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What is being tested?

The complete blood count (CBC) is a group of tests that evaluate the cells that circulate in blood, including red blood cells (RBCs), white blood cells (WBCs), and platelets (PLTs). The CBC can evaluate your overall health and detect a variety of diseases and conditions, such as infections, anemia and leukemia.

Blood cells are produced and mature primarily in the bone marrow and, under normal circumstances, are released into the bloodstream as needed. The three types of cells evaluated by the CBC include:

Red Blood Cells

Red blood cells, also called erythrocytes, are produced in the bone marrow and released into the bloodstream when they mature. They contain hemoglobin, a protein that transports oxygen throughout the body. The typical lifespan of an RBC is 120 days. Thus, the bone marrow must continually produce new RBCs to replace those that age and degrade or are lost through bleeding. A number of conditions can affect the production of new RBCs and/or their lifespan, in addition to those conditions that may result in significant bleeding.

RBCs normally are uniform in size and shape, but their appearance can be affected by a variety of conditions, such as vitamin B12 and folate deficiencies and iron deficiency. An example of a common condition affecting RBCs is anemia, which results from low red blood cell counts and low hemoglobin. Various diseases can lead to anemia, so additional tests are often needed to determine the cause. For more details, see the articles on Red Blood Cell Count, Hemoglobin, and Hematocrit.

White Blood Cells

White blood cells, also called leukocytes, are cells that exist in the blood, the lymphatic system, and tissues and are an important part of the body’s natural defense (immune) system. They help protect against infections and also have a role in inflammation, and allergic reactions. There are five different types of WBCs and each has a different function. They include neutrophils, lymphocytes, basophils, eosinophils, and monocytes.

WBCs are present in the blood at relatively stable numbers. However, these numbers may temporarily shift higher or lower depending on what is going on in the body. For instance, an infection can stimulate your bone marrow to produce a higher number of neutrophils to fight off a bacterial infection. With allergies, there may be an increased number of eosinophils. An increased number of lymphocytes may be produced with a viral infection. In certain diseases, such as leukemia, abnormal (immature or mature) white cells may rapidly multiply. For additional details, see the articles White Blood Cell Count and WBC Differential.

Platelets

Platelets, also called thrombocytes, are actually tiny cell fragments that circulate in blood and are essential for normal blood clotting. When there is an injury and bleeding begins, platelets help stop bleeding by adhering to the injury site and clumping together to form a temporary plug. They also release chemical signals that attract and promote clumping of additional platelets and eventually become part of a stable blood clot at the site of the injury that remains in place until the injury heals.

If you have a disease or condition that causes low platelets (thrombocytopenia) or dysfunction of platelets, you may be at an increased risk of excessive bleeding and bruising. An excess of platelets (thrombocytosis) can cause excessive clotting. For more information, see the article Platelet Count.

What is included in a CBC?

A CBC is typically performed using an automated instrument that measures various parameters, including cell counts and the physical features of some of the cells. A standard CBC includes:

Red blood cell (RBC) tests:

  • Red blood cell (RBC) count is a count of the actual number of red blood cells in your blood sample.
  • Hemoglobin measures the total amount of the oxygen-carrying protein in the blood, which generally reflects the number of red blood cells in the blood.
  • Hematocrit measures the percentage of your total blood volume that consists of red blood cells.
  • Red blood cell indices provide information on the physical features of the RBCs:
    • Mean corpuscular volume (MCV) is a measurement of the average size of your red blood cells.
    • Mean corpuscular hemoglobin (MCH) is a calculated measurement of the average amount of hemoglobin inside your red blood cells.
    • Mean corpuscular hemoglobin concentration (MCHC) is a calculated measurement of the average concentration of hemoglobin inside your red blood cells.
    • Red cell distribution width (RDW) is a measurement of the variation in the size of your red blood cells.
  • The CBC may also include reticulocyte count, which is a measurement of the absolute count or percentage of newly released young red blood cells in your blood sample.

White blood cell (WBC) tests:

  • White blood cell (WBC) count is a count of the total number of white blood cells in your blood sample.
  • White blood cell differential may be included as part of the CBC or may be done in follow up if the WBC count is high or low. The WBC differential identifies and counts the number of the five types of white blood cells present (neutrophils, lymphocytes, monocytes, eosinophils, and basophils). The individual count can be reported as an absolute count and/or as a percentage of total.

Platelet tests:

  • The platelet count is the number of platelets in your blood sample.
  • Mean platelet volume (MPV) may be reported with a CBC. It is a measurement of the average size of platelets.
  • Platelet distribution width (PDW) may also be reported with a CBC. It reflects how uniform platelets are in size.

CBC results that are outside the established reference intervals may indicate the presence of one or more diseases or conditions. Typically, other tests are performed to help determine the cause of abnormal results. Often, a blood smear will be examined using a microscope. A trained laboratory professional will evaluate the appearance and physical features of the blood cells, such as size, shape and color, noting any abnormalities that may be present. This information gives the healthcare practitioner additional clues as to the cause of abnormal CBC results.

Common Questions

How is the test used?

The complete blood count (CBC) is often used as a broad screening test to determine your general health status. A CBC may be used to:

  • Screen for a wide range of conditions and diseases
  • Help diagnose various diseases and conditions, such as anemia, infection, inflammation, bleeding disorder or leukemia, to name just a few
  • Monitor the status of a disease or condition and the effectiveness of treatment after a diagnosis is established
  • Monitor treatment that is known to adversely affect blood cells, such as chemotherapy or radiation therapy

When is it ordered?

The CBC is a very common test. You may have a CBC performed when you have a routine health examination.

A CBC may be ordered when you are ill and/or have signs and symptoms that may be related to conditions that affect blood cells. The test may be ordered when you have fatigue or weakness, or easy bruising or bleeding, or when you have signs and symptoms suggesting an infection or inflammation, to name a few examples.

When you have been diagnosed with a disease known to affect blood cells, a CBC will often be ordered on a regular basis to monitor the status of your disease/condition. Likewise, if you are being treated for a blood-related disorder, then a CBC may be performed frequently to determine if the treatment is effective.

Some therapies, such as chemotherapy, can affect bone marrow production of cells. Some medications can decrease WBC counts overall. A CBC may be ordered on a regular basis to monitor these drug treatments.

What does the test result mean?

A healthcare practitioner typically evaluates and interprets results from the components of the CBC together. Depending on the purpose of the test, a number of additional or follow-up tests may be ordered for further investigation.

For additional details, see the tables in the section Details on CBC Results below that briefly and generally explain what the result for each component of the CBC may mean.

To see an example of a CBC lab report, see this sample report.

My CBC report includes a result for immature granulocytes (IG). What are they?

Some automated hematology analyzers report the total number of immature granulocytes (IG) present in your blood sample. Immature granulocytes are white blood cells that have not fully developed before being released from the bone marrow into the blood. They may include metamyelocytes, myelocytes, and promyelocytes. These cells are normally only present in the bone marrow because they are precursors of neutrophils, the predominant type of white cells in blood. The presence of immature granulocytes in the blood may occur in various diseases, such as infection or a blood cancer, and thus will often prompt further investigation, which may include additional laboratory testing.

My CBC report includes a result for immature platelet fraction (IPF). What is it?

IPF is the relative number of newly released young platelets (also called reticulated platelets) in the blood. Platelets are produced in the bone marrow and are normally not released into the bloodstream until they have matured. When platelet numbers in the blood are low (thrombocytopenia), it stimulates the bone marrow to produce platelets faster. When the need is great and when production cannot keep up with “demand,” then an increased number of young platelets will be present in the bloodstream.

This IPF test result would be one of the values reported when blood is evaluated using an automated hematology analyzer. The IPF may be used to help a healthcare provider determine the likely cause of your thrombocytopenia:

  • A low IPF suggests a decrease in platelet production by the bone marrow.
  • A high IPF suggests an increased loss of platelets in peripheral blood.

Lab test results including platelet count and IPF can also help determine if you need a platelet transfusion and help monitor bone marrow recovery, such as after a bone marrow transplant. Other uses are being studied and the test’s ultimate clinical utility has not yet been well determined.

My CBC report includes a result for reticulocyte hemoglobin. What is it?

The hemoglobin inside of reticulocytes can be measured and reported as either a mean reticulocyte hemoglobin content (CHr) or a reticulocyte hemoglobin equivalent (Ret-He), depending upon the test method used. This test result would be one of the values reported when blood is evaluated using an automated hematology analyzer.

Reticulocytes are “young” red blood cells that are released by the bone marrow. They exist in blood for only 1-2 days before becoming fully mature. The amount of hemoglobin inside of reticulocytes can help determine your body’s iron status, particularly the availability of iron to be incorporated into hemoglobin in developing red blood cells in the bone marrow, within the past few days. This makes the test useful in identifying functional iron deficiency in certain clinical conditions (e.g., after treatment with erythropoietin) and in assessing iron deficiency anemia in children.

What diseases can a CBC detect?

A CBC can help detect a number of conditions. Some examples include:

If I have an abnormal result on my CBC, what other tests might my healthcare practitioner order as follow up?

It depends on the results that are abnormal and the suspected disease or condition as well as your medical history and findings from your physical examination. Your healthcare provider may request that a blood smear examination be done. Other general tests to check your health and to look for possible causes may include a comprehensive metabolic panel (CMP). A few other general examples include:

When a serious condition such as leukemia, lymphoma, myelodysplasia or another bone marrow disorder is suspected, then a bone marrow aspiration and biopsy may be necessary. Numerous other tests specific for certain conditions may be needed to establish a diagnosis, such as flow cytometry, chromosome analysis, and/or gene mutation analysis. Talk to your healthcare provider about the results of your CBC, whether additional tests are necessary, and why.

Is there anything else I should know?

Many different conditions can result in increases or decreases in blood cell populations. Some of these conditions may require treatment, while others may resolve on their own.

Recent blood transfusions affect the results of the CBC.

Normal reference CBC values for babies and children are different from adults. The laboratory will supply the reference intervals for various age groups, and a healthcare practitioner will take these into consideration when interpreting data.

Details on CBC Results

Red Blood Cell (RBC) Tests

For detailed information on each test component, click on the name of the component to go to the specific article.

To see an example of a CBC lab report, see this sample report.

Note: The reference ranges provided here represent a theoretical guideline that should not be used to interpret your test results. Some variation is likely between these numbers and the reference range reported by the lab that ran your test. Please consult your doctor. For more information on reference ranges, please read Reference Ranges and What They Mean.

Reference ranges listed here are for adults older than 18 years old. They are not available for youths 0-18 years old due to wide variability. See the child’s lab report for reference ranges.

Conventional Units are typically used for reporting results in U.S. labs. SI Units are used to report lab results outside of the U.S.

TEST Reference Range2 Examples of causes of low result Examples of causes of high result
Red Blood Cell Count
(RBC)		 Conventional Units

Men: 4.5-5.9 x 106/microliter

Women: 4.1-5.1 x 106 microliter

SI Units

Men: 4.5-5.9 x 1012/L

Women: 4.1-5.1 x 1012/L

 Known as anemia

 Known as polycythemia

  • Dehydration
  • Lung (pulmonary) disease
  • Kidney or other tumor that produces excess erythropoietin
  • Smoking
  • Living at high altitude
  • Genetic causes (altered oxygen sensing, abnormality in hemoglobin oxygen release)
  • Polycythemia vera—a rare disease
Hemoglobin

(Hb)

 Conventional Units

Men: 14-17.5 g/dL

Women: 12.3-15.3 g/dL

SI Units

Men: 140-175 g/L

Women: 123-153 g/L

 Usually mirrors RBC results, provides added information Usually mirrors RBC results
Hematocrit

(Hct)

 Conventional Units

Men: 41.5-50.4%

Women: 35.9-44.6%

SI Units

Men: 0.415-0.504 volume fraction

Women: 0.359-0.446 volume fraction

 Usually mirrors RBC results Usually mirrors RBC results; most common cause is dehydration
RBC indices
MCV Conventional Units

80-96 micrometer3

SI Units

80-96 fL

 Indicates RBCs are smaller than normal (microcytic); caused by iron deficiency anemia or thalassemias, for example. Indicates RBCs are larger than normal (macrocytic), for example in anemia caused by vitamin B12 or folate deficiency, myelodysplasia, liver disease, hypothyroidism, etc.
MCH Conventional Units

27.5-33.2 pg

SI Units

27.5-33.2 pg

 Mirrors MCV results; small red cells would have a lower value. Mirrors MCV results; macrocytic RBCs are large so tend to have a higher MCH.
MCHC Conventional Units

33.4-35.5 g/dL

SI Units

334-355 g/L

 May be low when MCV is low; decreased MCHC values (hypochromia) are seen in conditions such as iron deficiency anemia and thalassemia. Increased MCHC values (hyperchromia) are seen in conditions where the hemoglobin is more concentrated inside the red cells, such as autoimmune hemolytic anemia, in burn patients, and hereditary spherocytosis, a rare congenital disorder.
RBC Distribution Width (RDW, RDW-SD, RDW-CV)

Not always reported

 Indicates that RBC are uniform in size. Indicates mixed population of small and large RBCs; young RBCs tend to be larger. For example, in iron deficiency anemia or pernicious anemia, there is high variation (anisocytosis) in RBC size (along with variation in shape – poikilocytosis), causing an increase in the RDW.
Reticulocyte Count

Not always done

 Conventional Units

0.5-1.5% or
25-125 x 103/microliter

SI Units

0.005-0.015 number fraction or
25-125 x 109/L

 In the setting of anemia, a low reticulocyte count indicates a condition is affecting the production of red blood cells, such as bone marrow disorder or damage, or a nutritional deficiency (iron, B12 or folate). In the setting of anemia, a high reticulocyte count generally indicates peripheral cause, such as bleeding or hemolysis, or response to treatment (e.g., iron supplementation for iron deficiency anemia).

1 from Wintrobe’s Clinical Hematology. 14th ed. Greer J, editor. Philadelphia, PA: Wolters Kluwer: 2019.

2 from Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. McPherson R, Pincus M, eds. Philadelphia, PA: Elsevier Saunders; 2011.

White Blood Cell (WBC) Tests

For detailed information on each test component, click on the name of the component to go to the specific article.

To see an example of a CBC lab report, see this sample report.

Note: The reference ranges provided here represent a theoretical guideline that should not be used to interpret your test results. Some variation is likely between these numbers and the reference range reported by the lab that ran your test. Please consult your doctor. For more information on reference ranges, please read Reference Ranges and What They Mean.

Reference ranges listed here are for adults older than 18 years old. They are not available for youths 0-18 years old due to wide variability. See the child’s lab report for reference ranges.

Conventional Units are typically used for reporting results in U.S. labs. SI Units are used to report lab results outside of the U.S.

Test Reference Range2 Examples of causes of a low count Examples of causes of a high count
White Blood Cell Count

(WBC)

 

 Conventional Units1

4,500-11,000 white blood cells per microliter (mcL)

SI Units1

4.5-11.0 x 109 per liter (L)

 Known as leukopenia

 Known as leukocytosis
White Blood Cell Differential

(Diff)

 (Not always performed; may be done as part of or in follow up to CBC)
Absolute neutrophil count, % neutrophils

(Neu, PMN, polys)

 Conventional Units

Percent (mean): 56%

Absolute count (per microliter):
1800-7800

SI Units

Mean number fraction: 0.56

Absolute count X 109 per liter:
1.8-7.8

 Known as neutropenia

  • Severe, overwhelming infection (sepsis)
  • Autoimmune disorders
  • Dietary deficiencies
  • Reaction to drugs
  • Immunodeficiency
  • Myelodysplasia
  • Bone marrow damage (e.g., chemotherapy, radiation therapy)
  • Cancer that spreads to the bone marrow
  • Congenital neutropenia
 Known as neutrophilia

  • Acute bacterial infections
  • Inflammation
  • Trauma, heart attack, or burns
  • Stress, rigorous exercise
  • Certain leukemias (e.g., chronic myeloid leukemia)
  • Cushing syndrome
Absolute lymphocyte count, % lymphocytes

(Lymph)

 Conventional Units

Percent (mean) 34%
Absolute count (per microliter):
1000-4800

SI Units

Mean number fraction: 0.34
Absolute count X 109 per liter:
1.0-4.8

 Known as lymphocytopenia

 Known as lymphocytosis
Absolute monocyte count, % monocytes
(Mono)		 Conventional Units

Percent (mean) 4%
Absolute count (per microliter)
0-800

SI Units

Mean number fraction 0.04
Absolute count X 109 per liter
0-0.80

 Usually, one low count is not medically significant.

Repeated low counts can indicate:
  • Chronic infections (e.g., tuberculosis, fungal infection)
  • Infection within the heart (bacterial endocarditis)
  • Collagen vascular diseases (e.g., lupus, scleroderma, rheumatoid arthritis, vasculitis)
  • Monocytic or myelomonocytic leukemia (acute or chronic)
Absolute eosinophil count, % eosinophils

(Eos)

 Conventional Units

Percent (mean) 2.7%
Absolute count (per microliter)
0-450

SI Units

Mean number fraction 0.027
Absolute count X 109 per liter
0-0.45

 Numbers are normally low in the blood. One or an occasional low number is usually not medically significant.
Absolute basophil count, % basophils

(Baso)

 Conventional Units

Percent (mean) 0.3%
Absolute count (per microliter)
0-200

SI Units

Mean number fraction 0.030
Absolute count X 109 per liter
0-0.20

 As with eosinophils, numbers are normally low in the blood; usually not medically significant
  • Rare allergic reactions (hives, food allergy)
  • Inflammation (rheumatoid arthritis, ulcerative colitis)
  • Some leukemias
  • Uremia

1 from Wintrobe’s Clinical Hematology. 14th ed. Greer J, editor. Philadelphia, PA: Wolters Kluwer: 2019.

2 from Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. McPherson R, Pincus M, eds. Philadelphia, PA: Elsevier Saunders; 2011.

Platelet Tests

For detailed information on each test component, click on the name of the component to go to the specific article.

To see an example of a CBC lab report, see this sample report.

Note: The reference ranges provided here represent a theoretical guideline that should not be used to interpret your test results. Some variation is likely between these numbers and the reference range reported by the lab that ran your test. Please consult your doctor. For more information on reference ranges, please read Reference Ranges and What They Mean.

Reference ranges listed here are for adults older than 18 years old. They are not available for youths 0-18 years old due to wide variability. See the child’s lab report for reference ranges.

Conventional Units are typically used for reporting results in U.S. labs. SI Units are used to report lab results outside of the U.S.

Test Reference Range2 Examples of causes of low result Examples of causes of high result
Platelet Count

(Plt)

 Conventional Units

150-450 x 103/microliter

SI Units

150-450 x 109/L

 Known as thrombocytopenia:

 Known as thrombocytosis:
MPV

(Not always reported)

 Mean Platelet Volume Indicates average size of platelets is small; older platelets are generally smaller than young ones and a low MPV may mean that a condition is affecting the production of platelets by the bone marrow. Indicates a high number of larger, younger platelets in the blood; this may be due to the bone marrow producing and releasing platelets rapidly into circulation.
PDW

(Not always reported)

 Platelet Distribution Width Indicates uniformity in size of platelets. Indicates increased variation in the size of the platelets, which may mean that a condition is present that is affecting platelets.

1 from Wintrobe’s Clinical Hematology. 14th ed. Greer J, editor. Philadelphia, PA: Wolters Kluwer: 2019.

2 from Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. McPherson R, Pincus M, eds. Philadelphia, PA: Elsevier Saunders; 2011.

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You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”

For more information, please read the article Reference Ranges and What They Mean.

Related Media

Health Professionals – LOINC

LOINC Observation Identifiers Names and Codes (LOINC®) is the international standard for identifying health measurements, observations, and documents. It provides a common language to unambiguously identify things you can measure or observe that enables the exchange and aggregation of clinical results for care delivery, outcomes management, and research. Learn More.

Listed in the table below are the LOINC with links to the LOINC detail pages. Please note when you click on the hyperlinked code, you are leaving Lab Tests Online and accessing Loinc.org.

LOINC LOINC Display Name
47288-6 CBC WO Differential panel (BldCo)
57021-8 CBC W Auto Differential panel (Bld)
57022-6 CBC W Reflex Manual Differential panel (Bld)
57782-5 CBC W Ordered Manual Differential panel (Bld)
58410-2 CBC panel Auto (Bld)
69742-5 CBC W Differential panel, method unspecified (Bld)
74412-8 CBC W Differential panel (BldCo)
95215-0 CBC W Differential panel (Stem cell product)

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