CBC Test Normal Range: Your Complete Blood Count Explained

What a CBC test measures

A CBC counts and measures the cells in a small sample of blood:

• Red blood cells (RBC) carry oxygen from the lungs to the rest of the body.
• Haemoglobin (Hb) is the iron-rich protein inside red cells that actually carries the oxygen.
• Haematocrit (HCT or PCV) is the share of the blood made up of red cells.
• Red cell indices: MCV is the average size of red cells, MCH the average amount of haemoglobin in each cell, and MCHC the haemoglobin concentration relative to cell size. These help a doctor work out what kind of anaemia someone has.
• White blood cells (WBC) fight infection. A "CBC with differential" also counts each of the five main types of white cell.
• Platelets help the blood clot and stop bleeding.

In India the test is also called a complete haemogram or full blood count. At our centre it is listed as CBC under Blood Test in the tests catalogue.

CBC test normal range

The MedlinePlus Medical Encyclopedia gives these as common adult results. Blood counts can vary with altitude, and every laboratory sets its own reference range, so the range printed on your report is the one to use.

The table is for adults. If the report is for a child, ask our paediatrician to interpret it rather than comparing it with an adult table.

What high or low values can mean

Low haemoglobin, RBC or haematocrit is a sign of anaemia. The World Health Organization describes anaemia as haemoglobin falling below set thresholds that depend on age, sex and pregnancy, and treats it as a symptom of an underlying cause rather than a disease in itself. MedlinePlus lists causes such as iron deficiency, blood loss (including heavy periods over a long time), poor intake of iron, folate or vitamin B12, long-term kidney disease and other chronic illness, and, less often, bone marrow problems.

High haemoglobin or haematocrit can be caused by dehydration, for example after severe diarrhoea or heavy sweating, as well as smoking, long-term lung or heart disease and some rarer conditions.

High WBC most often reflects an infection, but it can also follow some medicines such as steroids, severe stress or tissue injury, and, rarely, blood cancers. Low WBC can follow viral infections, some medicines, autoimmune disease or bone marrow problems.

Low platelets (thrombocytopenia) means a count below 150,000 per mcL. MedlinePlus notes that below 50,000 the risk of bleeding is higher. Dengue is one cause of a falling count: India's national dengue guidelines list a rapid fall in platelets together with a rising haematocrit as a warning sign. See our guide to dengue tests and when to take them.

Do you need to fast for a CBC?

No. MedlinePlus says no special preparation is usually needed. The sample is taken from a vein in the arm and the draw usually takes less than five minutes. If your doctor has ordered other tests at the same time, such as fasting sugar or a lipid profile, follow the fasting time for those; our guide on fasting blood test preparation explains how.

Tell the staff about any medicines you take, and drink water normally, since dehydration can push some values up.

Reading your report sensibly

• Values marked high or low are not a diagnosis. MedlinePlus points out that diet, activity, medicines, menstrual periods and not drinking enough water can all move results.
• Trends matter. In conditions such as dengue or anaemia treatment, doctors watch how counts change over days or weeks. Keep your old reports and bring them with you.
• A CBC is one tool. It points the doctor in a direction, and further tests may follow, for example iron studies for anaemia or a HbA1c test, whose result can itself be affected by anaemia.