Health And Safety

The complete blood count (CBC) is often used as a broad screening test to determine an individual's general health status. It can be used to:

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

A CBC is a panel of tests that evaluates the three types of cells that circulate in the blood and includes the following:

• Evaluation of white blood cells, the cells that are part of the body's defense system against infections and cancer and also play a role in allergies and inflammation:
  • White blood cell (WBC) count is a count of the total number of white blood cells in a person's sample of blood.
  • White blood cell differential may or may not be included as part of the panel of tests. It identifies and counts the number of the various types of white blood cells present. The five types include neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
• Evaluation of red blood cells, the cells that transport oxygen throughout the body:
  • Red blood cell (RBC) count is a count of the actual number of red blood cells in a person's sample of blood.
  • Hemoglobin measures the amount of the oxygen-carrying protein in the blood.
  • Hematocrit measures the percentage of a person's blood that consists of red blood cells.
  • Red blood cell indices are calculations that provide information on the physical characteristics of the RBCs:
    • Mean corpuscular volume (MCV) is a measurement of the average size of RBCs.
    • Mean corpuscular hemoglobin (MCH) is a calculation of the average amount of oxygen-carrying hemoglobin inside a red blood cell.
    • Mean corpuscular hemoglobin concentration (MCHC) is a calculation of the average percentage of hemoglobin inside a red cell.
    • Red cell distribution width (RDW), which may be included in a CBC, is a calculation of the variation in the size of RBCs.
  • The CBC may also include reticulocyte count, which is a measurement of the absolute count or percentage of young red blood cells in blood.
• Evaluation of platelets, cell fragments that are vital for normal blood clotting:
  • The platelet count is the number of platelets in a person's sample of blood.
  • Mean platelet volume (MPV) may be reported with a CBC. It is a calculation of the average size of platelets.
  • Platelet distribution width (PDW) may also be reported with a CBC. It is a measurement of the variation of platelet size.

The CBC is a very common test. Many people have a CBC performed when they have a routine health examination. If a person is healthy and has results that are within normal limits, then he or she may not require another CBC until their health status changes or until their doctor feels that it is necessary.
A CBC may be ordered when a person has any number of signs and symptoms that may be related to disorders that affect blood cells. When an individual has fatigue or weakness or has an infection, inflammation, bruising, or bleeding, a doctor may order a CBC to help diagnose the cause and/or determine its severity.
When a person has been diagnosed with a disease known to affect blood cells, a CBC will often be ordered on a regular basis to monitor their condition. Likewise, if someone is receiving treatment 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.

A doctor 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.
The following tables briefly and generally explain what the result for each component of the CBC may mean.

• WBC evaluation
• RBC evaluation
• Platelet evaluation

Components of the CBC

WBC Evaluation 

Test	FUll Name	examples of causes of a low count	examples of causes of a high count
WBC	White Blood Cell Count	Known as leukopenia Bone marrow disorders or damage Autoimmune conditions Severe infections (sepsis) Lymphoma or other cancer that spread to the bone marrow Diseases of immune system (e.g., HIV)	Known as leukocytosis Infection, most commonly bacterial or viral Inflammation Leukemia, myeloproliferative disorders Allergies, asthma Tissue death (trauma, burns, heart attack) Intense exercise or severe stress
Diff	White Blood Cell Differential (Not always performed; may be done as part of or in follow up to CBC)
Neu, PMN, polys	Absolute neutrophil count, % neutrophils	Known as neutropenia Severe, overwhelming infection (sepsis) Autoimmune disorders Reaction to drugs, chemotherapy Immunodeficiency Myelodysplasia Bone marrow damage (e.g., chemotherapy, radiation therapy) Cancer that spreads to the bone marrow	Known as neutrophilia Acute bacterial infections Inflammation Tissue death (necrosis) caused by trauma, heart attack, burns Physiological (stress, rigorous exercise) Certain leukemias (e.g., chronic myeloid leukemia)
Lymph	Absolute lymphocyte count, % lymphocytes	Known as lymphocytopenia Autoimmune disorders (e.g., lupus, rheumatoid arthritis) Infections (e.g., HIV, viral hepatitis, typhoid fever, influenza) Bone marrow damage (e.g., chemotherapy, radiation therapy) Corticosteroids	Known as lymphocytosis Acute viral infections (e.g., chicken pox, cytomegalovirus (CMV), Epstein-Barr virus (EBV), herpes, rubella) Certain bacterial infections (e.g., pertussis (whooping cough), tuberculosis (TB)) Toxoplasmosis Chronic inflammatory disorder (e.g., ulcerative colitis) Lymphocytic leukemia, lymphoma Stress (acute)
Mono	Absolute monocyte count, % monocytes	Usually, one low count is not medically significant. Repeated low counts can indicate: Bone marrow damage or failure Hairy cell leukemia	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)
Eos	Absolute eosinophil count, % eosinophils	Numbers are normally low in the blood. One or an occasional low number is usually not medically significant	Asthma, allergies such as hay fever Drug reactions Parasitic infections Inflammatory disorders (celiac disease, inflammatory bowel disease) Some cancers, leukemias or lymphomas
Baso	Absolute basophil count, % basophils	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

RBC Evaluation 

Test	Full Name	examples of causes of low result	examples of causes of high result
RBC	Red Blood Cell Count	Known as anemia Acute or chronic bleeding RBC destruction (e.g., hemolytic anemia, etc.) Nutritional deficiency (e.g., iron deficiency, vitamin B12 or folate deficiency) Bone marrow disorders or damage Chronic inflammatory disease Kidney failure	Known as polycythemia Dehydration Lung (pulmonary) disease Kidney or other tumor that produces excess erythropoietin Smoking Genetic causes (altered oxygen sensing, abnormality in hemoglobin oxygen release) Polycythemia vera—a rare disease
Hb	Hemoglobin	Usually mirrors RBC results, provides added information	Usually mirrors RBC results
Hct	Hematocrit	Usually mirrors RBC results	Usually mirrors RBC results; most common cause is dehydration
RBC indices
MCV	Mean Corpuscular Volume	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
MCH	Mean Corpuscular Hemoglobin	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	Mean Corpuscular Hemoglobin Concentration	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.
RDW (Not always reported)	RBC Distribution Width	Low value indicates uniformity in size of RBCs	Indicates mixed population of small and large RBCs; immature 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)	Reticulocytes (absolute count or %)	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)

Platelet Evaluation 

Test	FUll Name	examples of causes of low result	examples of causes of high result
Plt	Platelet Count	Known as thrombocytopenia: Viral infection (mononucleosis, measles, hepatitis) Rocky mountain spotted fever Platelet autoantibody Drugs (acetaminophen, quinidine, sulfa drugs) Cirrhosis Autoimmune disorders Sepsis Leukemia, lymphoma Myelodysplasia Chemo or radiation therapy	Know as thrombocytosis: Cancer (lung, gastrointestinal, breast, ovarian, lymphoma) Rheumatoid arthritis, inflammatory bowel disease, lupus Iron deficiency anemia Hemolytic anemia Myeloproliferative disorder (e.g., essential thrombocythemia)
MPV (Not always reported)	Mean Platelet Volume	Indicates average size of platelets is small; older platelets are generally smaller than younger 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

Many different conditions can result in increases or decreases in the 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 CBC values for babies and children are different from adults. The laboratory will supply the reference ranges for various age groups, and the doctor will take these into consideration when interpreting data.