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What is a CBC Test?
A Complete Blood Count (CBC) is one of the most commonly ordered blood tests in medicine. It measures the three main types of cells in your blood: red blood cells (RBCs), white blood cells (WBCs), and platelets. By analyzing these components, doctors get a detailed picture of your overall health and can detect a wide range of conditions — from anemia and infections to clotting disorders and blood cancers.
What Does a CBC Measure?
A standard CBC report includes:
- Hemoglobin (Hb) — the protein in red blood cells that carries oxygen. Low levels indicate anemia.
- Red Blood Cell Count (RBC) — the total number of red blood cells per unit of blood.
- White Blood Cell Count (WBC) — elevated in infections or inflammation; low in certain immune disorders.
- Platelet Count — essential for blood clotting. Very low levels (thrombocytopenia) can cause bleeding; very high levels increase clot risk.
- Hematocrit (HCT) — the percentage of blood volume made up of red blood cells.
- MCV, MCH, MCHC — describe the size and hemoglobin content of red blood cells, helpful in classifying anemia types.
- Differential WBC count — breaks down white blood cells into types (neutrophils, lymphocytes, monocytes, etc.) to identify the nature of an infection or immune response.
Normal CBC Values for Adults
- Hemoglobin: Men 13.5–17.5 g/dL | Women 12.0–15.5 g/dL
- WBC: 4,000–11,000 cells/μL
- Platelets: 150,000–400,000 cells/μL
- RBC: Men 4.5–5.9 million/μL | Women 4.1–5.1 million/μL
Values outside these ranges do not always mean disease — your doctor will interpret results alongside your symptoms and medical history.
When Should You Get a CBC?
A CBC is ordered for routine health checkups, to investigate symptoms like fatigue, weakness, frequent infections, unusual bruising, or prolonged bleeding. It is also used to monitor ongoing conditions like anemia or to check the effect of treatments like chemotherapy. If you have dengue fever, a CBC is essential to track platelet count.
Preparation for CBC Test
No special preparation is typically required. You do not need to fast. However, stay well hydrated before the test to make blood collection easier, and inform your doctor of any medications you are taking, especially blood thinners, steroids, or iron supplements.