Complete blood count

A complete blood count (CBC) is a blood test that evaluates the cells that circulate
in the blood.
It is used to evaluate overall health and detect a wide range of disorders,
including anemia, infection, leukemia etc.
Synonyms: Complete blood cell count, full blood count (FBC), full blood exam
(FBE).

 Specimen: Whole blood, usually collected by venipuncture.
 Collection: EDTA tube (purple/lavender top) containing EDTA potassium salt
additive as an anticoagulant.
 Panels: Complete blood count (CBC)
NOTE:
EDTA (Ethylene Diamine Tetra-Acetate)

Blood consists of three types of cells suspended in fluid called plasma: white blood
cells (WBCs), red blood cells (RBCs), and platelets (PLTs).
They are produced and mature primarily in the bone marrow and, under normal
circumstances, are released into the bloodstream as needed.
A CBC is typically performed using an automated instrument that measures
various parameters, including counts of the cells that are present in a person's
sample of blood.

A standard CBC includes the following:
a) Evaluation of white blood cells: WBC count; may or may not include a WBC
differential.
b) Evaluation of red blood cells: RBC count, hemoglobin (Hb), hematocrit (Hct) and
RBC indices, which includes mean corpuscular volume (MCV), mean
corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration
(MCHC), and red cell distribution width (RDW). The RBC evaluation may or
may not include reticulocyte count.
c) Evaluation of platelets: platelet count (PLT); may or may not include mean
platelet volume (MPV) and/or platelet distribution width (PDW).

So a complete blood count test measures several components and features of your
blood:
 Red blood cells (RBC), which carry oxygen.
 White blood cells (WBC), which fight infection.
 Hemoglobin (Hb), the oxygen-carrying protein in red blood cells.
 Hematocrit (Hct), the proportion of red blood cells to the fluid component, or
plasma, in your blood.
 Platelets (PLT), which help with blood clotting.
A trained laboratorian can evaluate the appearance and physical characteristics of
the blood cells, such as size, shape and color, noting any abnormalities that may be
present.
Significant abnormalities in one or more of the blood cell populations can indicate the
presence of one or more conditions.

Red blood cells, also called erythrocytes, are produced in the bone marrow and
released into the bloodstream as they mature.
They contain hemoglobin, a protein that transports oxygen throughout the body.
The typical lifespan of an RBC is 120 days;
The CBC determines the number of RBCs and amount of hemoglobin present, the
proportion of blood made up of RBCs (hematocrit), and whether the population of
RBCs appears to be normal.

1) RED BLOOD CELL COUNT (RBC).
 It's also known as an erythrocyte count. Is used to find out how many red blood
cells (RBCs) present in a patient’s sample blood.
REFERENCE RANGE:
 Men: 4.5-5.9 x 106/microliter,
 Women: 4.1-5.1 x 106/microliter.

EXAMPLES OF CAUSES OF LOW RESULT EXAMPLES OF CAUSES OF HIGH RESULT
 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
 Chronic kidney disease
 Known as polycythemia.
 Living at high altitude
 Smoking
 Polycythemia vera—a rare disease
 Dehydration
 Lung (pulmonary) disease
 Kidney or other tumor that produces excess
erythropoietin
 Genetic causes (altered oxygen sensing,
abnormality in hemoglobin oxygen release)

2) HAEMOGLOBIN (HB).
Concentration of haemoglobin within the blood.
Hb is the protein which carries oxygen in the blood and, hence, is the most
important value to look at. Low Hb = Anaemia.
REFERENCE RANGE:
 Men: 14-17.5 g/dL
 Women: 12.3-15.3 g/dL

Examples of causes of low/high results, Usually mirrors RBC results and provides
added information.
Check the previous table for examples.

3) HEMATOCRIT (HCT).
Also known as Packed Cell Volume (PCV); Volume percentage of red blood cells in
the blood.
REFERENCE RANGE:
 Men: 41.5-50.4%
 Women: 35.9-44.6%

Examples of causes of low/high results, Usually mirrors RBC results and provides
added information.
But most common cause of raised Hct is dehydration.
Check the previous table for other examples.

4. RBC INDICES.
are blood tests that provide information about the hemoglobin content and size of
red blood cells.
They are used to help diagnose the cause of anemia, a condition in which there are
too few red blood cells and other disorders of RBC.
These are:-
i. Mean corpuscular/cell volume (MCV),
ii. Mean corpuscular hemoglobin (MCH),
iii. Mean corpuscular hemoglobin concentration (MCHC),
iv. Red cell distribution width (RDW), and
v. Reticulocyte Count (Not always done)
NOTE: Corpuscular = Cell

i. MEAN CORPUSCULAR VOLUME (MCV).
Also known as Mean cell volume: is the average volume of a red blood cell.
Literally, it measures the average size of your red blood cells (“-cytic”)
This is the main method used to classify anaemia.
REFERENCE RANGE:
SI Unit: 80-96 fL
Conventional Unit: 80-96 micrometer3

Low results, Indicates RBCs are smaller than normal (microcytic); caused by iron
deficiency anemia or thalassemias to mention a few.
High results, Indicates RBCs are larger than normal (macrocytic), for example
in anemia caused by vitamin B12 or folate deficiency, myelodysplasia, liver
disease, hypothyroidism

ii. MEAN CORPUSCULAR HEMOGLOBIN (MCH).
Also known as Mean Cell hemoglobin: is the content (weight) of hemoglobin (Hb)
of the average red cell, or, in other words, a reflection of hemoglobin mass in red
cells.– affects the color of the cells (“-chromic”).
MCH can be used to determine if an anemia is hypo-, normo-, or hyperchromic.
MCV has to be considered along with the MCH since cell volume/size (MCV)
affects the content of hemoglobin present per cell (MCH), and MCH can decrease
or increase in parallel to the MCV.
MCHC in the past has been thought to be a better parameter than MCH to
determine hypochromasia. These days after multichannel analyzer it does not
add significant, clinically relevant information.
REFERENCE RANGE:
 27.5-33.2 pg (picograms/cell).

Most normocytic and microcytic anemias are normochromic
Most microcytic anemias are hypochromic (Except anemia of chronic diseases)
Decreased MCH values (hypochromia) mirrors MCV (Microcytic) results: and seen
in conditions such as iron deficiency anemia and thalassemia.
Increased MCH values (hyperchromia) Mirrors MCV (macrocytic) results; RBCs
are large so tend to have a higher MCH.

iii. MEAN CORPUSCULAR HEMOGLOBIN CONCENTRATION
(MCHC).
 Also known as Mean cell hemoglobin concentration: is the average concentration
of hemoglobin in a given volume of packed red blood cells, or in other words, the
ratio of hemoglobin mass to the volume of red cells.
REFERENCE RANGE:
 33.4-35.5 g/dL

MCHC, when increased, can be useful clinically as an indicator of increased
spherocytes (spherocytosis), as in hereditary spherocytosis or autoimmune
hemolytic anemia. It is also increased in homozygous sickle cell or hemoglobin C
disease.
Normochromic normocytic anemia: normal MCV, normal MCH and normal MCHC
Microcytic hypochromic anemia: low MCV, low MCH and low MCHC
Macrocytic normochromic anemia: high MCV, high MCH and normal MCHC
Normal MCH and elevated MCHC is seen in hereditary spherocytosis

iv. RED CELL DISTRIBUTION WIDTH (RDW).
measures variation in RBC size or RBC volume as a part of a complete blood count (CBC). It
is used in conjunction with MCV to determine if anemia is due to a mixed cause or a single
cause.
Elevated RDW(red blood cells of unequal sizes) = “anisocytosis“ and variation in shape =
“poikilocytosis”
Therefore, MCV together with red cell distribution width (RDW) have become the two most
useful parameters in classifying anemias, while MCH and MCHC allow laboratories to detect
potential causes of erroneous results, such as hyperlipidemia or hemolysis (both in vivo and
in vitro), so the correct results can be reported.
REFERENCE RANGE: RDW can be reported statistically as coefficient of variation (CV)
and/or standard deviation (SD)
 RDW-SD 39-46 fL
 RDW-CV 11.6-14.6% in adult
NOTE: Reference ranges may vary depending on the individual laboratory and patient's age.

Considerations
Elevated RDW provides a clue for heterogenous red cell size (anisocytosis) and/or
the presence of 2 red cell populations while other RBC indices (MCV, MCH and
MCHC) reflect average values and may not adequately reflect RBC changes where
mixed RBC populations are present, such as dimorphic RBC populations in
sideroblastic anemia or combined iron deficiency anemia (decreased MCV and
MCH) and megaloblastic anemia (increased MCV).
Peripheral blood smear review can help confirm the above findings in these
circumstances.

Normal RDW and normal MCV is associated with the following conditions:
 Anemia of chronic disease
 Acute blood loss or hemolysis
 Anemia of renal disease
Normal RDW and low MCV are associated with the following conditions:
 Anemia of chronic disease
 Heterozygous thalassemia
 Hemoglobin E trait
Normal RDW and high MCV are associated with the following conditions:
 Aplastic anemia
 Chronic liver disease
 Chemotherapy/antivirals/alcohol

High RDW and normal MCV is associated with the following conditions:
 Early iron, vitamin B12, or folate deficiency
 Dimorphic anemia (for example, iron and folate deficiency)
 Sickle cell disease
 Myelodysplastic syndrome
High RDW and low MCV are associated with the following conditions:
 Iron deficiency
 Sickle cell-β-thalassemia

High RDW and high MCV are associated with the following conditions:
 Folate or vitamin B12 deficiency
 Immune hemolytic anemia
 Cytoxic chemotherapy
 Myelodysplastic syndrome

v. RETICULOCYTE COUNT.
Is the concentration of immature RBC in a volume of blood.
Reticulocytes are immature, but already anucleated RBCs with residual
detectable amounts of RNA, thereby capable of producing hemoglobin despite
anucleation.
Increased in blood loss and hemolytic anemia because the bone marrow works
harder to replace lost cells.
REFERENCE RANGE:
 in adults is 0.5%-1.5%.
NOTE: Each laboratory should determine reference values according to their own
methods and instruments.

Increased reticulocyte count reflects ongoing or recent RBC production activity, which
may result from the following:
 Post bleeding (trauma, gastrointestinal bleeding, menorrhagia)
 Post hemolysis (hemolytic anemia, hemolytic disease of the newborn)
 Response to therapy (iron supplementation, vitamin B-12 or folic acid supplementation,
erythropoietin supplementation, bone marrow recovery following chemotherapy or bone
marrow transplantation)
A decreased reticulocyte count reflects decreased RBC production, which may result from
the following:
 Vitamin B-12, folic acid, and iron deficiency (megaloblastic anemia, pernicious
anemia, iron deficiency anemia)
 Decreased erythropoietin level (chronic renal failure)
 Aplastic anemia or bone marrow failure syndromes
 Post radiation therapy
 Bone marrow replacement by benign (metabolic storage diseases, infection, sarcoidosis)
or malignant processes (leukemias, involvement by lymphomas or metastatic tumors)

also called leukocytes, that the body uses to maintain a healthy state and to fight
infections or other causes of injury.
There are five different types of WBCs, these are neutrophils, lymphocytes,
basophils, eosinophils and monocytes.
The white blood cells (leukocytes) are further divided into phagocytes or myeloid
(neutrophils, eosinophils, basophils, monocytes) and immunocytes or lymphoid
(lymphocytes).
They are present in the blood at relatively stable numbers. These numbers may
temporarily shift higher or lower depending on what is going on in the body.
The total white blood cell count is expressed as an absolute number and is further
divided into subtypes of white blood cells by a differential WBC count, which is
expressed as a percentage and absolute number.

1) WHITE BLOOD CELL COUNT
Also known as Leukocytes count.
 A white blood cell (WBC) count of less than 4 x 109/L indicates leukopenia. While
a WBC count of more than 11 x 109/L indicates leukocytosis.
REFERENCE RANGE:
Total leukocytes:
 SI Units :4.5-11.0 x 109 per liter (L)
 Conventional Units :4,500-11,000 white blood cells per microliter (mcL)

Decreased WBC count, leukopenia, is seen when supply is depleted by infection or
treatment such as chemotherapy or radiation therapy, or when a hematopoietic
stem cell abnormality does not allow normal growth/maturation within the bone
marrow, such as myelodysplastic syndrome or leukemia.
Elevated WBC, leukocytosis, is seen in response to infection, stress, inflammatory
disorders (referred to as reactive leukocytosis), or abnormal production as in
leukemia.

i. NEUTROPHIL COUNT. (Neu, PMN, polys)
Neutrophils are a type of white blood cell (WBC or granulocyte) that protect a body
against infections.
are the first cells to arrive on the scene when we experience a bacterial infection.
are the most abundant type of granulocytes and the most abundant (60% to 70%) type of
white blood cells in most mammals. They form an essential part of the innate immune
system.
REFERENCE RANGE:
SI Units
 Mean number fraction: 0.56
 Absolute count : 1.8-7.8 X 109 per liter
Conventional Units
 Percent (mean): 56%
 Absolute count (per microliter): 1800-7800 /mcL

EXAMPLES OF CAUSES OF A LOW COUNT EXAMPLES OF CAUSES OF A HIGH
COUNT
Known as leukopenia
 Bone marrow disorders or damage, post-
chemotherapy
 Autoimmune conditions, hypersplenism
 Severe infections (sepsis)
 Lymphoma or other cancer that spread to
the bone marrow
 Diseases of immune system
(e.g., HIV/AIDS)
 Agranulocytosis causing drugs (4C’s:
Carbamazepine, Carbimazole, Clozapine,
Colchicine)
Known as leukocytosis
 Infection, most commonly acute bacterial
 Inflammation, necrosis
 Leukemia, myeloproliferative neoplasms
 Allergies, asthma
 Tissue death (surgery, trauma, burns, heart
attack)
 Intense exercise or severe stress
 Corticosteroids

ii. LYMPHOCYTE COUNT. (Lymph)
 Lymphocytes are type of white blood cell (leukocyte) that is of fundamental
importance in the immune system, They are made in the bone marrow and found in
the blood and lymph tissue.
 They are the main type of cell found in lymph, which prompted the name
"lymphocyte".
 Lymphocytes include natural killer cells (which function in cell-
mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic adaptive
immunity), and B cells (for humoral, antibody-driven adaptive immunity).
REFERENCE RANGE:
 SI Units
 Mean number fraction: 0.34
 Absolute count : 1.0-4.8 X 109 per liter
 Conventional Units
 Percent (mean) 34%
 Absolute count (per microliter): 1000-4800/mcL

EXAMPLES OF CAUSES OF A LOW COUNT EXAMPLES OF CAUSES OF A HIGH COUNT
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 chronic bacterial infections
(e.g.pertussis (whooping cough), tuberculosis
(TB))
 Toxoplasmosis
 Chronic inflammatory disorder (e.g.
ulcerative colitis)
 Lymphocytic leukemia (CLL), lymphoma
 Stress (acute)

iii. MONOCYTE COUNT (MONO)
Monocytes are the largest type of leukocyte and can differentiate into
macrophages and myeloid lineage dendritic cells.
monocytes are important in the immune system's ability to destroy invaders, but
also in facilitating healing and repair.
REFERENCE RANGE:
 SI Units
 Mean number fraction 0.04
 Absolute count : 0 - 0.80X 109 per liter
 Percent (mean) 4%
 Absolute count (per microliter) : 0 – 800 /mcL

Known as monocytopenia.
Usually, one low count is not medically
significant. Repeated low counts can indicate:
 Aplastic anemia
 Bone marrow damage or failure
 Hairy cell leukemia
 Corticosteroids
 Acute infection
Known as Monocytosis.
 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)
 Autoimmune diseases
 Hodgkin’s disease

iv. EOSINOPHIL COUNT. (Eos)
Eosinophils, sometimes called less commonly, acidophils, are a variety of white blood
cells and one of the immune system components responsible for combating
multicellular parasites and certain infections.
Most often indicates a parasitic infection, an allergic reaction or cancer.
REFERENCE RANGE:
 SI Units
 Absolute count : 0 - 0.45 X 109 per liter
 Percent (mean) 2.7%
 Absolute count (per microliter) : 0-450 /mcL

EXAMPLES OF CAUSES OF A LOW
COUNT
EXAMPLES OF CAUSES OF A HIGH COUNT
Known as Eosinopenia
 Numbers are normally low in the
blood. One or an occasional low
number is usually not medically
significant.
Known as Eosinophilia.
 Asthma
 Allergies such as hay fever, eczema
 Parasitic infections
 Drug reactions
 Inflammatory disorders (celiac
disease, inflammatory bowel disease)
 Some cancers, leukemias or lymphomas
 Addison disease
 Hyper-eosinophilic syndrome

v. BASOPHIL COUNT (Baso)
Basophils are a member of the granulocytes, the white blood cells in the circulation,
and constitute less than 1% of the circulating leukocytes.
Basophils and mast cells share functional similarities and are involved
in immediate hypersensitivity reactions as well as chronic inflammatory or
immunologic responses.
REFERENCE RANGE:
 SI Units
 Absolute count : 0 - 0.20 X 109 per liter
 Percent (mean) 0.3%
 Absolute count (per microliter) : 0-200 /mcL

EXAMPLES OF CAUSES OF A LOW COUNT EXAMPLES OF CAUSES OF A HIGH
COUNT
Known as Basopenia.
 As with eosinophils, numbers are normally
low in the blood; usually not medically
significant.
Known as Basophilia.
 Rare allergic reactions (hives, food allergy)
 Inflammation (rheumatoid arthritis,
ulcerative colitis)
 Some leukemias /Lymphoma
• Uremia
• IgE mediated hypersensitivity
• Myeloproliferative disorders

Platelets, also called thrombocytes, are special cell fragments that play an
important role in normal blood clotting.
A person who does not have enough platelets may be at an increased risk of
excessive bleeding and bruising.
An excess of platelets can cause excessive clotting or, if the platelets are not
functioning properly, excessive bleeding.
The CBC measures the number and size of platelets present through:
i. Platelet count
ii. Mean platelet volume
iii. Platelet distribution width

i. PLATELET COUNT (Plt)
Measures how many platelets present in the patient’s blood sample.
REFERENCE RANGE:
 SI Units :150-450 x 109/L
 Conventional Units :150-450 x 103/microliter

Known as thrombocytopenia:
 Viral infection (mononucleosis, measles,
hepatitis)
 Aplastic anemia
 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)

ii. MEAN PLATELET VOLUME (MPV)
Mean platelet volume (MPV) is a measure of the average size of platelets in a
given blood sample.
REFERENCE RANGE:
 9.4–12.3 fL (femtolitre)
NOTE: Reference ranges may vary depending on the individual laboratory and
patient's age.

MPV is a marker of platelet activation, Platelets with a higher volume are more
active.
 The mean platelet volume tends to be higher when the platelet count is lower, e.g.
In a patient with thrombocytopenia (below normal platelet count), a high MPV
suggests that the bone marrow is compensating by producing new platelets.
 However, thrombocytopenia associated with a low MPV is more consistent with
the suppression of cell production by the bone marrow (aplastic anemia or
congenital abnormality).
A high MPV seems to be associated with a cardiovascular risk and an increased
risk of thrombosis (phlebitis, etc.). In a person who has no history of bleeding and
a normal platelet count, an abnormal PMV is of less clinical usefulness.

 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.

iii. Platelet Distribution Width (PDW)
Is a regular parameter in CBC which reflects variation of platelet size distribution.
EXAMPLES OF CAUSES OF A LOW
COUNT
EXAMPLES OF CAUSES OF A HIGH
COUNT
 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

 Wintrobe's Clinical Hematology. 12th ed. Greer J, Foerster J, Rodgers G, Paraskevas
F, Glader B, Arber D, Means R, eds. Philadelphia, PA: Lippincott Williams & Wilkins:
2009.
 Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed.
McPherson R, Pincus M, eds. Philadelphia, PA: Elsevier Saunders; 2011.
 Medscape 2019. Leukocyte Count (WBC), retrieved on 20th September 2019,
https://emedicine.medscape.com/article/2054452-overview#showall
 Medscape 2019. Red blood cell indices, retrieved on 20th September 2019,
https://emedicine.medscape.com/article/2054497-overview#showall
 Lab tests online last modified on June 14, 2019. Complete Blood Count (CBC),
retrieved on 20th September 2019, https://labtestsonline.org/tests/complete-blood-
count-cbc
 OSCE stop. Source of free OSCE exam notes for medical students’ final revision 2013,
Interpretation of the full blood count, viewed on 20th September 2019,
http://www.oscestop.com/FBC_interpretation.pdf

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