Complete blood count (CBC) is a test to review overall health and determine various conditions such as anemia, some infections and leukemia etc. The test measures various components of the blood including red blood cells (RBCs), hemoglobin (Hb), hematocrit (Hct), total leucocyte count (TLC), mean corpuscular volume (MCV), packed cell volume (PCV), platelets and erythrocyte sedimentation rate (ESR). Each type of the blood cells should function well because these have specific set of actions that are important for proper functioning of the body.
Also Known as
A blood sample drawn from a vein in the arm or a fingerstick or heelstick (newborns)
How the Test is Done?
In this process, RBCs breakdown to release hemoglobin that combines with potassium cyanide to form a compound called ‘cyanmethemoglobin’. The produced compound is then measured through an apparatus utilizing light absorption capacity of the compound over a range of wavelength (spectrophotometric technique). Electrical Impedance: The method utilizes electric resistance of the blood cells to measure their volume and hence their numbers. A blood sample is diluted using an electrolytic diluent (electric conductor in nature) and is pulled through a small opening having an electrode on either side of it. Electric current passes through the electrodes continuously. The electrical resistance formed between the electrodes is directly proportional to the cell volume when cells pass through the opening.
What all does the test include?
The main components of complete blood count include:
There are also other components of complete blood count which includes:
Abnormality in these parameters may indicate underlying disease or condition that need further investigations.
How to Prepare Before the Test?
No preparation is required, you can drink and eat normally.
Why to Take the Test?
Your doctor may ask you to undergo a CBC test due to the following reasons:
If there are signs and symptoms like fatigue, weakness, bruising or fever.
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 when you are receiving treatment known to affect blood cells
If the results are within the reference range, then these are considered normal. Abnormally high or low result values may indicate an underlying medical condition. You should contact doctor for further evaluation in such cases.
Red blood cells, hemoglobin and hematocrit
Low: If the levels in these parameters is below the reference range, it may indicate anemia. Anemia can occur due to various reasons such as iron and vitamin deficiency, hemophilia, HIV, cancer, kidney or liver diseases etc.
High: If parameters are higher than the reference range, it could be due to polycythemia or heart diseases.
Total Leucocyte count
Low: Deceased levels may indicate autoimmune disorders (e.g. ankylosing spondylitis), bone marrow disease or cancer.
High: Increased levels may indicate inflammatory condition (rheumatoid arthritis) or infection.
Low: If the count is below the normal value it is known as thrombocytopenia, may be due to diseases like hemophilia.
High: If the count is above the normal value it is known as thrombocytosis, it may be caused by conditions like thrombocythemia, lymphoma, gastrointestinal cancer etc.
Low: Lower than normal value may be due to the conditions that increase RBC production.
High: Elevated level may indicate inflammation, infection, pregnancy or ageing.
Packed cell volume (PCV)
Low: Decreased level indicates red blood cell loss due to various reasons such as blood loss and failure of bone marrow production.
High: Increased level may indicate dehydration or increased production of red blood cells.
Mean corpuscular hemoglobin (MCH)
Low: Lower than normal value may be due to iron deficiency anemia, microcytic anemia (RBC size is too small) or celiac disease.
High: Higher than normal value may indicate liver disease, overactive thyroid, taking estrogen medications in excess amount.
Mean corpuscular volume (MCV)
Low: Lower than normal value may indicate microcytic anemia, it can be caused by iron deficiency.
High: Higher than normal value may indicate macrocytic anemia, it can be due to alcoholism or deficiency of vitamin B12/folic acid.
Mean corpuscular hemoglobin concentration (MCHC)
Low: Decreased level may indicate that RBCs do not have enough amount of hemoglobin that can lead to iron deficiency anemia.
High: Increased level can be due to burns causing hemolytic anemia or liver disease damaging RBCs.
Red cell distribution width
Low: Lower than normal value may indicate macrocytic anemia due to a deficiency of folate, iron or vitamin B12 or chronic liver disease.
High: Higher than normal value may indicate aplastic anemia.
Low: Decreased neutrophils count may indicate neutropenia that can be due to chemotherapy, radiation, leukemia, or vital illness.
High: Increased count may indicate bacterial infection, acute inflammation, burn, or heart attack.
Low: Low level may indicate lymphocytopenia also known as lymphopenia, marked decrease in count can be due to infection or other significant illness.
High: Higher level may indicate infection or inflammation and sometimes it can be due to leukemia.
Low: Low level may indicate monocytopenia caused by chemotherapy, blood infection or bone marrow infection.
High: High level may indicate chronic infection, autoimmune disorder or cancer.
Low: Low level may indicate alcohol abuse or Cushing's disease. Lower levels are not of concern unless other components of white cell counts are also affected.
High: High level may indicate eosinophilia caused by a parasitic infection, allergic reaction or cancer.
Low: Low level may indicate basopenia and may be caused by drug induced reactions, elevated levels of glucocorticoids or overactive thyroid.
High: Low level may indicate basophilia and may occur due to chronic myelogenous leukemia, allergic rhinitis, inflammatory bowel syndrome.
CBC (20 Tests):
People may respond differently during a blood sample collection. Some people might feel nausea, dizziness, sweating, or drop in blood pressure and rarely may faint. Whereas, others may remain absolutely normal.
The reason, they might feel sick during sample collection is vasovagal reaction which is a physical response of the nervous system that gets stimulated by seeing a needle or blood or feeling anxious about the procedure.
Complete blood count is often ordered by your doctor to understand the overall health status of an individual and to rule out conditions such as anemia and infections etc.
In general, there is a very low risk associated with the test. Rarely, bruising, bleeding, swelling or infection at the insertion site have been seen.
Individuals with bleeding disorders or taking blood thinning medications (e.g. aspirin, warfarin) should inform their doctor and technician before undergoing a blood collection test to avoid the risk of bleeding.
The frequency of the test will be determined by your doctor. If there is any underlying medical condition such as anemia, hemophilia, leukemia or certain type of cancers then more frequent testing may be required.
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