A full or complete blood count (CBC) is a blood test used to evaluate your overall health and detect a wide range of disorders, including anemia, infection and leukemia. A complete blood count test measures several components and features of your blood, including:
- Red blood cells, which carry oxygen
- White blood cells, which fight infection
- Hemoglobin, the oxygen-carrying protein in red blood cells
- Hematocrit, 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 you have an underlying medical condition that calls for further evaluation.
Why it is done
A complete blood count is a common blood test that’s done for a variety of reasons:
- To review your overall health : Your doctor may recommend a complete blood count as part of a routine medical examination to monitor your general health and to screen for a variety of disorders, such as anemia or leukemia.
- To diagnose a medical condition : Your doctor may suggest a complete blood count if you’re experiencing weakness, fatigue, fever, inflammation, bruising or bleeding. A complete blood count may help diagnose the cause of these signs and symptoms. If your doctor suspects you have an infection, the test can also help confirm that diagnosis.
- To monitor a medical condition : If you’ve been diagnosed with a blood disorder that affects blood cell counts, your doctor may use complete blood counts to monitor your condition.
- To monitor medical treatment : A complete blood count may be used to monitor your health if you’re taking medications that may affect blood cell counts.
Normal Results Values
The following are normal complete blood count results for adults. Note that:
(L = litre mcL = microliter dL = deciliter)
Red blood cell count
Male: 4.32-5.72 trillion cells/L
(4.32-5.72 million cells/mcL)
Female: 3.90-5.03 trillion cells/L (3.90-5.03 million cells/mcL)
Male: 13.5-17.5 grams/dL (135-175 grams/L).
Female: 12.0-15.5 grams/dL (120-155 grams/L)
Male: 38.8-50.0 percent.
Female: 34.9-44.5 percent
White blood cell count
3.5-10.5 billion cells/L (3,500 to 10,500 cells/mcL)
150-450 billion/L (150,000 to 450,000/mcL)
What the results may indicate
Results in the following areas above or below the normal ranges on a complete blood count may indicate a problem.
- Red blood cell count, hemoglobin and hematocrit – The results of your red blood cell count, hemoglobin and hematocrit are related because they each measure aspects of your red blood cells. If the measures in these three areas are lower than normal, you have anemia. Anemia causes fatigue and weakness. Anemia has many causes, including low levels of certain vitamins or iron, blood loss, or an underlying condition. A red blood cell count that’s higher than normal (erythrocytosis), or high hemoglobin or hematocrit levels, could point to an underlying medical condition, such as polycythemia vera or heart disease.
- White blood cell count – A low white blood cell count (leukopenia) may be caused by 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 normal, you may have an infection or inflammation. Or, it could indicate that you have an immune system disorder or a bone marrow disease. A high white blood cell count can also be a reaction to medication.
- Platelet count – A platelet count that’s lower than normal (thrombocytopenia) or higher than normal (thrombocytosis) is often a sign of an underlying medical condition, or it may be a side effect from medication. If your platelet count is outside the normal range, you’ll likely need additional tests to diagnose the cause.
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