Complete Blood Count (CBC) Test – A Complete Guide
Understand CBC test, normal ranges, preparation, and what your results indicate.
A Complete Blood Count (CBC) is one of the most commonly ordered blood tests. It gives a broad picture of your overall health and helps detect a wide range of disorders, including anaemia, infection, and blood cancers. A single small blood sample can reveal a great deal about how your body is functioning.
What is a CBC Test?
A CBC measures the different types of cells in your blood — red blood cells (RBCs), white blood cells (WBCs), and platelets — along with related parameters like haemoglobin, haematocrit, and MCV. It is a screening test that helps doctors monitor your health and diagnose conditions.
What Does a CBC Measure?
- RBC Count: Number of red blood cells that carry oxygen.
- Haemoglobin (Hb): Protein in RBCs that binds oxygen.
- Haematocrit (HCT): Percentage of blood volume made up of RBCs.
- WBC Count: Immune cells that fight infection.
- Platelets: Cells that help blood clot.
- MCV, MCH, MCHC: Indices that describe RBC size and haemoglobin content.
Normal CBC Ranges (Adults)
- Haemoglobin: 13.5–17.5 g/dL (men), 12.0–15.5 g/dL (women)
- RBC: 4.5–5.9 million/µL (men), 4.1–5.1 million/µL (women)
- WBC: 4,000–11,000 cells/µL
- Platelets: 150,000–450,000 /µL
- Haematocrit: 38.8–50.0% (men), 34.9–44.5% (women)
Preparation for the Test
A CBC generally does not require fasting. However, if it is being taken along with other tests (like lipid profile or glucose), your doctor may ask you to fast for 8–12 hours. Stay hydrated and inform the lab about any medications or supplements you are taking.
What Do Your Results Mean?
- Low Haemoglobin: May indicate anaemia, blood loss, or nutritional deficiencies.
- High WBC: Often points to infection, inflammation, or in some cases leukaemia.
- Low Platelets: Can cause easy bruising and bleeding.
- High RBC: May suggest dehydration or an underlying lung/heart condition.
When Should You Get a CBC Done?
Get a CBC done annually as part of a routine check-up, or if you experience persistent fatigue, weakness, unexplained fever, easy bruising, or recurrent infections. Doctors also use CBC to monitor patients on chemotherapy or long-term medications.
