Complete Blood Count (CBC)
Common Components of the CBC
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Red blood cell count
Hemoglobin (Hgb)
Hematocrit (Hct)
Platelets (PLT)
White blood cell count
White blood cell differential
Red Blood Cells (RBCs)
Red Blood Cell (RBC) Count: 3.6-5.4
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RBC count range: 3.6-5.4
RBCs transport oxygen to body tissues. Body tissues that are adequately oxygenated are
said to be well-perfused
High levels may indicate dehydration. This is because the blood becomes less diluted
with dehydration, so the number of RBCs will be more concentrated
Low levels indicate a lack of oxygen, malnutrition, or blood loss. Low RBCs levels from
blood loss results in hypovolemia (low fluid volume in the vasculature) secondary to
hemorrhage. Common causes of hemorrhage include trauma, post-operative
complications, and adverse effects from certain medications that reduce the viscosity of
the blood (such as heparin and warfarin)
Routine use of IV fluid replacement commonly leads to low levels that are unrelated to a
pathology. This is because the blood becomes hypervolemic (high fluid volume in the
vasculature). Small alterations are usually not concerning. However, risks exists when IV
fluids are used excessively, causing fluid overload. This can be particularly dangerous to
patients with heart disease as increased fluid volume may raise the blood pressure,
leading to elevated systemic vascular resistance (SVR) and increasing the cardiac
preload, making the heart work harder to pump blood. Furthermore, hypervolemia from
overhydration can also cause crucial electrolyte values to become deficient in comparison
(such as sodium and potassium)
Hemoglobin (Hgb)
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Hemoglobin (Hgb) range: ♥ 12-16 gm/dL; ♠ 13.8-17.2 gm/dL
Criteria for anemia for both boys and girls that are 3-12 years of age: hemoglobin
level less than 11.0 g/dL
Hemoglobin is the oxygen-carrying pigment found in RBCs. Each hemoglobin contains a
heme group that binds with iron molecules (up to 4). Although hemoglobin levels are
evaluated to predict oxygen transport, they only reveal the number of molecules available
to bind to red blood cells, rather than the actual number of red blood cells that are
saturated in oxygen
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Anemia is linked to low hemoglobin levels. Anemia, which is a symptom of a condition
rather than an actual disease in of its own right, is characterized by low red blood cell
levels but is actually measured by the hemoglobin values. Broad causes of anemia
include poor nutritional status (either from diet or secondary to an absorption issue), an
acute disease state, or a chronic pathology that either renders the baseline hemoglobin
levels low (as in the hemoglobin is always low in the patient) or can cause acute
exacerbations that temporarily affect levels (such as cases of sickle cell anemia, when the
individual experiences a “sickle cell crisis” or another exacerbation).The underlying
cause of anemia is determined by analyzing a combination of hematological findings.
These include hemoglobin, mean corpuscular volume (MCV), mean corpuscular
hemoglobin (MCH), and the mean corpuscular hemoglobin concentrate (MCHC)
Hemoglobin levels are often used to determine if a patient needs a blood transfusion. The
cut-off point varies between facility policies, but most mandate transfusion for values
under 7-8 gm/dL
Low hemoglobin values are seen in patients with hemoglobinopathies, or inherited
blood disorders that either affect hemoglobin structure or synthesis. The most common
include thalassemia syndromes, including alpha-thalassemia and beta-thalassemia (βthalassemia), and structural hemoglobin variants (abnormal hemoglobins), including HbS
(sickle cell anemia), HbE, and HbC. As expected, a major symptom of
hemoglobinopathies is anemia
Hematocrit
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Hematocrit (Hct): ♥ 37-47%; ♠ 41-50%
Hct is the percentage of red blood cells present in the blood (the
‘composition’). Testing is an important indicator in diagnosing anemia and
narrowing down the type of etiology in which it originates
A high hematocrit can suggest fluid deficit or dehydration
A low hematocrit can suggest fluid overload. Patients on intravenous fluids often
experience a slightly decreased hematocrit as their blood becomes ‘diluted.’ It may also
be present in anemia related to poor nutrition, renal insufficiency, or bone marrow
suppression
Platelets
Platelet Count
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Platelet count range: 130,000-400,000 per microliter
Platelets are the most abundant yet smallest type of blood cell. They are actually cellular
fragments that originate from megakaryocytes. They have a 8-10 day life span and play a
vital role in coagulation
Thrombocytopenia, or a low platelet count, may be related to failure of the bone marrow
to produce enough platelets or can indicate an infection, vitamin deficiency, or a
medication that affects coagulation, such as heparin (an anticoagulant that’s often
administered following surgery as prophylaxis for deep vein thrombosis). Heparin
induced thrombocytopenia (HIT) is seen in patients that develop an immune reaction to
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heparin use; therefore, patients that are given heparin should have their platelet counts
monitored. Acquired thrombocytopenia may occur following chemotherapy due to bone
marrow destruction
High platelet counts can increase blood viscosity and place a patient at risk for stroke
Inherited low platelet counts, such as those seen in genetics blood disorders, places the
patient at risk for excessive bleeding
Mean Platelet Volume (MPV)
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MPV range: 9.4-12.3 FL
The MCV is a platelet marker
High levels of MCV have been linked to an increased risk of risk of thrombosis. Highgrade inflammatory diseases are often associated with low levels.
White Blood Cells (WBCs)
White Blood Cell (WBC) Count
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WBC count range: 5.0-10 mm3
Standard evaluation included in the CBC to assess for signs of infection or to determine a
baseline
The two components include the overall WBC count and the differential. The differential
looks at the composition of each individual type of cell in the overall WBC population
WBCs are more diagnostically valuable by considering the individual cell types that
compose the WBC count
White blood cells are also called leukocytes
Leukopenia, a low WBC count, can result from chemotherapy, antibiotics, or bone
marrow dysfunction
Severe infections can result in leukemoid reaction in which the WBC count becomes
incredibly high
Absolute lymphopenia is defined as WBC count less than 1,500 mm3; it’s most common
in immunocompromised viral infections such as AIDS
A “shift to the left” is a term used to denote that an increase in leukocytes, especially
neutrophils, meaning that the cellular population is characterized by immature precursors,
rather than segmented or matured neutrophils
Neutrophils
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Neutrophil range: 48-73%
Neutrophilia (+) is often present with certain acute infections that form pus
It can also be related to mental stress
Neutropenia (-) is seen in aplastic anemia, following chemotherapy for certain
malignancies such as acute myeloid leukemias, extreme dietary deficiencies, or during
severe infections, signaling a long and overwhelming battle with pathogen that may
possibly have gone septic
Lymphocytes
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Lymphocytes range: 20-40%
Lymphocytes include B cells and T cells
Lymphocytosis (+) is present in acute infections, such as mononucleosis or hepatitis, and
during radiation exposure
Lymphocytopenia (-) often occurs with sepsis and in leukemia
This test is ordered to evaluate T-Cells, B-Cells, and to monitor for signs of infection
Monocytes
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Monocyte range: 0-9%
Monocytosis (+) is seen in cases of tuberculosis, viral infections, and chronic
inflammatory disorders
Monocytopenia (-) can occur as the result of prednisone use
Eosinophils
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Eosinophil range: 0-5%
Eosinophilia (+) is common during parasitic infections, eczema, allergic reactions, and
some immune diseases
Eosinopenia (-) could be related to the increase of adrenosteroid production
Ordered to evaluate for the presence of an infection, especially parasitic, or immune
diseases and allergies
Basophils
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Basophils 0-2%
Basophilia (+) is seen with myeloproliferative diseases and leukemia
Basopenia (-) is common in cases of allergic responses, stress, and hyperthyroidism
An increase is seen in the recovery phase of an infection
Bands
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Bands or stab cells are immature neutrophils
A “shift to the left” is a term that indicates increased immature white blood cell
production possibly related to a prolonged acute bacterial infection
Absolute Neutrophil Count (ANC)
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ANC range: 2500
An ANC under 1000 suggests a severe immunocompromised status and the need for
isolation
ANC = WBC x (% of neutrophils + % of bands)
Chemotherapy may severely reduce levels