Understanding Your Bloodwork
From the Mayo Clinic
A 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.The 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.
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.
If your blood sample is being tested only for a complete blood count, you can eat and drink normally before the test. If your blood sample will be used for additional tests, you may need to fast for a certain amount of time before the test. Your doctor will give you specific instructions.
For a complete blood count, a member of your health care team takes a sample of blood by inserting a needle into a vein in your arm, usually at the bend in your elbow. The blood sample is sent to a lab for analysis. You can return to your usual activities immediately.
A complete blood count is typically not a definitive diagnostic test. Depending on the reason your doctor recommended this test, results outside the normal range may or may not require follow-up. Your doctor may need to look at the results of a CBC along with results of other blood tests, or additional tests may be necessary.
For example, if you’re otherwise healthy and have no signs or symptoms of illness, results slightly outside the normal range on a complete blood count may not be a cause for concern, and follow-up may not be needed. However, if you’re undergoing cancer treatment, results of a complete blood count outside the normal range may indicate a need to alter your treatment plan.