A complete blood count (CBC) is the most commonly ordered blood test. From one small tube of blood it measures the three types of blood cells: red blood cells that carry oxygen, white blood cells (leucocytes) that fight infection, and platelets that help blood clot. This guide explains what each part of the report means, normal ranges, and common reasons for high or low counts, along with the related bleeding time test.
Quick answer: In adults, a normal white blood cell count is roughly 4,000 to 11,000 cells per microlitre, platelets 150,000 to 450,000 per microlitre, and hemoglobin about 13 to 17 g/dL in men and 12 to 15 g/dL in women. A high WBC count usually points to infection or inflammation; a low one can follow viral infections, some medicines or bone marrow problems. Low platelets are common in dengue and some other infections. No fasting is needed for a CBC.
Key takeaways
- ✅ Results slightly outside the range are common and often not significant; patterns matter more.
- ✅ The WBC "differential" shows which type of white cell is raised, which helps point to the cause.
- ✅ Platelets below 20,000, or any count with active bleeding, need urgent medical care.
- ✅ Always compare with your own lab's reference range.
What a CBC measures
| Parameter | Typical adult range | What it tells you |
|---|
| Hemoglobin (Hb) | Men 13–17 g/dL; women 12–15 g/dL | Oxygen-carrying capacity; low in anemia |
| Red blood cell (RBC) count | Men 4.5–5.5; women 3.8–4.8 million/µL | Number of red cells |
| Hematocrit / PCV | Men 40–50%; women 36–46% | Proportion of blood made up of red cells; rises with dehydration |
| MCV, MCH, MCHC | MCV about 80–100 fL | Size and colour of red cells; help classify anemia |
| RDW | About 11.5–14.5% | Variation in red cell size; often high in iron deficiency |
| Total leucocyte count (TLC/WBC) | 4,000–11,000/µL | Infection, inflammation, immunity and marrow health |
| Platelet count | 150,000–450,000/µL (1.5–4.5 lakh) | Clotting ability |
White blood cells: types and what they mean
| Type | Share of WBCs | Raised in | Lowered in |
|---|
| Neutrophils | 40–75% | Bacterial infections, inflammation, steroids, stress | Viral infections, chemotherapy, some medicines, severe infection |
| Lymphocytes | 20–40% | Viral infections, TB, some leukaemias | HIV, steroids, severe illness |
| Monocytes | 2–10% | Chronic infections such as TB, recovery from infection | Rarely significant alone |
| Eosinophils | 1–6% | Allergy, asthma, worm infestations | Steroids, acute stress |
| Basophils | 0–1% | Some allergies and blood disorders | Rarely significant |
High WBC count (leucocytosis) is most often due to infection, but also occurs with injury, surgery, steroids, smoking, pregnancy and, less commonly, leukaemia. Low WBC count (leucopenia) can follow viral illnesses such as dengue or typhoid, some medicines, vitamin B12 or folate deficiency, autoimmune disease and bone marrow disorders.
Platelet count
- Low platelets (thrombocytopenia): dengue and other viral infections, malaria, sepsis, some medicines, immune thrombocytopenia (ITP), liver disease with an enlarged spleen, and bone marrow disease. A falsely low count can happen if platelets clump in the tube, so an unexpected low result is often rechecked with a blood smear.
- High platelets (thrombocytosis): usually reactive to infection, inflammation, iron deficiency or recent surgery; rarely due to a bone marrow disorder.
Seek urgent care if low platelets come with bleeding gums, nosebleeds, blood in urine or stools, black stools, many new red spots or bruises, severe abdominal pain or vomiting, especially during dengue.
Bleeding time test
Bleeding time measures how long a small, standard skin cut takes to stop bleeding. It reflects how well platelets and small blood vessels work. Normal values are about 2 to 7 minutes by the Ivy method and 1 to 5 minutes by the Duke (earlobe) method. It may be prolonged with low or poorly working platelets, von Willebrand disease, aspirin and other antiplatelet medicines, and kidney failure. Because it is hard to standardise, many labs now prefer platelet function tests, and a normal bleeding time does not guarantee there will be no bleeding during surgery.
How the CBC is done
A small amount of blood is drawn from a vein into a tube containing EDTA, which stops clotting. An automated analyser counts and sizes the cells within minutes, and a peripheral smear may be examined under the microscope if anything looks unusual. No fasting is needed, but tell the lab about recent illness, medicines, pregnancy or heavy exercise, which can affect results.
Frequently asked questions
What platelet count is dangerous?
The risk of spontaneous bleeding rises when platelets fall below about 20,000 per microlitre, and especially below 10,000. But how you feel and whether you are bleeding matter as much as the number.
Can a CBC detect cancer?
It can suggest blood cancers such as leukaemia and show anemia caused by other cancers, but most cancers need other tests to diagnose.
Why is my WBC slightly high with no symptoms?
Smoking, stress, recent exercise, pregnancy and some medicines can raise it slightly. Your doctor may simply repeat the test later.
Related reading: Anemia: hemoglobin levels and causes and the ESR test.
Last updated: September 2026. General health and laboratory information only, not a diagnosis. Reference ranges vary between labs; please discuss your report with a qualified doctor.
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