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COMPLETE BLOOD COUNT: What You Need to Know.

A complete blood count (full haemoglobin) is a blood test used to evaluate the overall health of an individual and detect a wide range of disorders, including anaemia, infection and leukaemia.

A complete blood count test measures several components and features of the blood, including:
• Red blood cells, which carry oxygen
• White blood cells, which fight infection
• Haemoglobin, the oxygen-carrying protein in red blood cells
• Haematocrit, the proportion of red blood cells to the fluid component, or plasma, in your blood
• Platelets, which help with blood clotting

Abnormal increases or decreases in cell counts as revealed in a complete blood count may indicate that a patient has an underlying medical condition to warrant further evaluation.

Clinicians request a complete blood count for various reasons:
• To review the health of a patient. A clinician may recommend a full blood count as part of a routine medical examination to monitor the general health of a patient and to screen for a variety of disorders, such as anaemia or leukaemia.
• To diagnose a medical condition. A healthcare provider may carry out a complete blood count if a patient is experiencing symptoms such as weakness, fatigue, fever, or bleeding. A CBC may help diagnose the cause of these signs and symptoms. If a healthcare provider suspects a condition, the test can also help confirm that diagnosis.
• To monitor a medical condition. If a healthcare provider has diagnosed the patient with a blood disorder, they may use a complete blood count to track the disease progress.
• To monitor medical treatment. A healthcare provider may use a CBCount to monitor your health if you take medications that may affect blood cell count.

Equipment Needed.
• Vacutainers
• Sterile swab,
• Tourniquet
• Disposable gloves
• Syringe and needle,10ml

• Explain what you intend to do
• Perform hand hygiene and wear the gloves
• Apply the tourniquet and identify an accessible vein.
• Ensure the venipuncture site is sterile. Use an antiseptic (2% chlorhexidine in 70% alcohol solution). Allow to dry and don’t touch the area.
• Collect at least 20 ml blood in a syringe
• Dispense into the sample bottle and cover
• Label well with the name of patient and number, date and time you collected the samples.

Send the sample to the lab for the complete blood count.

The reference range for a complete blood count may differ slightly from one medical centre to the other. For the purpose of this discussion, we will use this reference range.
• White blood cells: 4,500 to 11,000 cells per microliter (cells/)
• Red blood cells: 4.5 million to 5.9 million cells/ L for men; 4.1 million to 5.1 million cells/L for women
• Haemoglobin: 14 to 17.5 grammes per deciliter (gm/dL) for men; 12.3 to 15.3 gm/dL for women
• Haematocrit: 41.5% to 50.4% for men; 35.9% to 44.6% for women
• Mean corpuscular volume: 80 to 96
• Platelets: 150,000 to 450,000 platelets/ µL

Results in the following areas above or below the normal ranges on a complete blood count may indicate a problem.

• Red blood cell count, haemoglobin and haematocrit. The results of your red blood cell count, haemoglobin and haematocrit are related because they each measure aspects of your red blood cells.
If the measures in these areas are lower than expected, the patient has anaemia. Anaemia causes fatigue and weakness. Anaemia has many causes, including low levels of specific vitamins or iron, blood loss, or an underlying condition.
A red blood cell count higher than expected, or high haemoglobin or haematocrit levels could point to an underlying medical condition, such as polycythaemia vera or heart disease.

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• White blood cell count. A low white blood cell count (leukopenia) may be due to a medical condition, such as an autoimmune disorder that destroys white blood cells, bone marrow problems or cancer. Certain medications also can cause white blood cell counts to drop.
If your white blood cell count is higher than expected, you may have an infection or inflammation or, an immune system disorder or a bone marrow disease. A high white blood cell count can also be a reaction to a medication.

• Platelet count. A platelet count lower or higher than expected is often a sign of an underlying medical condition or a side effect from the medication. If your platelet count is outside the normal range, you’ll likely need additional tests to diagnose the cause.

Other vital information we can obtain from a complete blood count include:

• Mean corpuscular haemoglobin (MCH). This test tells how much haemoglobin is in your typical red blood cell.
• Mean corpuscular haemoglobin concentration (MCHC). It measures the haemoglobin concentration in a certain amount of blood.
• Red cell distribution width (RDW). It shows how your much your red blood cells vary in size.
• Reticulocyte count. This test measures the number of new red blood cells in your body.
• Mean platelet volume (MPV). This result gives the average size of the platelets in your blood.
• Platelet distribution width (PDW). It shows how much your platelets vary in size.
• White blood cell differential. Five types of white blood cells exist – basophils, eosinophils, lymphocytes, monocytes, and neutrophils. This test shows how many of each kind you have.


A complete blood count (CBC) is a blood test used to evaluate your overall health and detect a wide range of disorders, including anaemia, infection and leukaemia.

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MBChB (MUK), Graduate Fellow, Department of Physiology, Makerere University Founder and Content Creator Peer reviewer, Associate Editor

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