A routine blood test that measures white blood cells, red blood cells, hemoglobin, hematocrit, and platelets. It is used to screen for anemia, infection, and clotting problems.
Indication
- Investigating anemia in a patient with fatigue, weakness, or pale skin
- Evaluating white blood cells in suspected fever and infection
- Routine pre-operative assessment
- Follow-up of chronic diseases (kidney, liver, rheumatologic)
- Platelet monitoring in bleeding or clotting problems
- Cell count monitoring in patients receiving chemotherapy
- Annual routine health check-up
Preparation
- Fasting is not required for CBC; it can be drawn at any time of day
- It is not recommended to draw blood immediately after intense exercise
- Inform the physician of medications used (especially blood thinners)
How it's performed
- About 2-3 mL of blood is drawn from the arm (usually from a vein in the inner elbow)
- The blood is placed in a purple-top (EDTA) tube and sent to the laboratory
- Cells are counted and ratios calculated by an automated hematology analyzer
- If abnormal findings are present, microscopic peripheral smear examination is added
- Results are usually available the same day
Post-procedure
- Results are interpreted by the physician together with clinical findings
- If anemia is detected, additional tests such as iron, B12, and folic acid may be requested
- If white blood cell or platelet abnormalities are found, hematology consultation is recommended
- If a follow-up test is needed, it is repeated at the interval specified by the physician
Risks
- Temporary bruising or tenderness at the blood draw site
- Rarely, a small hematoma at the needle site
- Transient dizziness in people with needle phobia
- Very rarely, local infection
FAQ
Do I need to fast for a complete blood count?
No, CBC does not require fasting. However, if other tests (such as fasting blood glucose) are also being run from the same draw, fasting may be requested.
What are the normal values?
In adults, approximate ranges are: WBC 4-10 thousand/µL, RBC 4.5-5.9 (men) / 4.0-5.2 (women) million/µL, hemoglobin 13.5-17.5 (men) / 12-16 (women) g/dL, hematocrit 40-52% (men) / 36-48% (women), and platelets (PLT) 150-400 thousand/µL. Small variations occur by age, sex, and laboratory.
How long do results take?
Most laboratories deliver results within 1-2 hours; the physician can review them the same day.
Can a CBC alone make a diagnosis?
No. It is used as a screening test; any abnormality detected is evaluated together with symptoms and additional investigations.
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