CBC
Complete Blood Count
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Category
Blood
Sample
Blood
Report Time
Same Day
Fasting
Not needed
About CBC
A Complete Blood Count (CBC) is one of the most frequently ordered blood tests in medicine, giving your doctor a detailed snapshot of the three main cell types circulating in your blood: red blood cells, white blood cells, and platelets.
The test measures hemoglobin (the oxygen-carrying protein in red cells), hematocrit (the proportion of blood made up of red cells), red and white cell counts, and a platelet count, along with several derived indices like MCV and MCH that describe the size and hemoglobin content of individual red cells.
Because it touches on so many body systems at once — oxygen transport, immune defense, and clotting — a CBC is used both as a routine screening tool during annual checkups and as a targeted diagnostic test when a doctor suspects anemia, infection, inflammation, or a blood disorder.
It's quick, requires only a small venous blood sample, and results are typically available the same day, which is why it's often the very first test ordered when a patient reports vague symptoms like fatigue or unexplained bruising.
What each part of the CBC tells you
Hemoglobin and hematocrit show the blood's oxygen-carrying capacity; low values mean anaemia. RBC count and indices (MCV, MCH, MCHC, RDW) describe the size and hemoglobin content of red cells and help identify the type of anaemia: small pale cells suggest iron deficiency or thalassaemia, large cells suggest B12 or folate deficiency. WBC count with differential shows infection-fighting cells: neutrophils rise in bacterial infection, lymphocytes in many viral infections, eosinophils in allergy and parasites. Platelets help clotting and fall in dengue and other conditions.
Common patterns doctors look for
- Low hemoglobin with low MCV: iron deficiency or thalassaemia trait; ferritin and iron studies help tell them apart.
- Low hemoglobin with high MCV: vitamin B12 or folate deficiency, liver disease or thyroid problems.
- High WBC with neutrophils: bacterial infection or inflammation.
- Low WBC: viral infections, certain medicines or bone marrow problems.
- Low platelets: dengue, other viral fevers, ITP, medicines; very low values need urgent attention.
- High hemoglobin: dehydration, smoking, living at altitude, or polycythaemia.
Why a CBC is ordered so often
CBC is one of the most common tests worldwide because it screens for anaemia, infection, inflammation and blood disorders in a single sample. It is a routine part of health check-ups, pre-operative work-ups, pregnancy care and monitoring of chemotherapy and many chronic diseases.
Normal values depend on you
Normal ranges differ with age, sex, pregnancy and altitude. Women have lower hemoglobin than men, children have different ranges, and pregnancy lowers hemoglobin through haemodilution. Always compare your values with the range printed on your report.
Booking a CBC
CBC is quick, with results often available within hours. Prices vary by lab and city, so compare on LabDekho and choose home collection if convenient. No fasting is required.
When Should You Get This Test?
Your doctor is likely to order a CBC if you're experiencing any of the following, or simply as part of a routine annual health checkup:
- Persistent fatigue, weakness, or unusual paleness
- Unexplained fever, chills, or frequent infections
- Unusual or easy bruising and bleeding
- Shortness of breath or a racing heartbeat
- Before a scheduled surgery or major medical procedure
- As part of monitoring a known chronic condition or ongoing medication
Because a CBC is so broadly informative, many doctors include it as a baseline test even when symptoms are mild or non-specific, since subtle abnormalities can point toward a problem well before it becomes serious.
Conditions This Test Can Detect
A single CBC can surface clues toward a wide range of conditions, which is part of why it remains such a cornerstone test:
- Iron-deficiency and other forms of anemia
- Bacterial or viral infections (typically shown by a raised white cell count)
- Blood cancers such as leukemia or lymphoma
- Clotting and bleeding disorders linked to low platelet counts
- Bone marrow disorders that affect cell production
- Dehydration, reflected in an elevated hematocrit
A CBC rarely gives a final diagnosis on its own — an abnormal result is usually the starting point for further, more targeted testing.
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How to Prepare
- No fasting is required for a standard CBC, so you can eat and drink normally beforehand unless it's being drawn alongside another test that does require fasting.
- Wear a short-sleeved or loose-sleeved top to make it easy for the phlebotomist to access a vein in your arm.
- Mention any medications, supplements, or recent illnesses to the lab staff, since some of these can subtly influence cell counts.
- Stay well hydrated before your appointment, as this makes the blood draw itself easier and more comfortable.
Normal Reference Ranges
Reference ranges differ slightly by lab, method, and by the patient's age and sex — always read your CBC report alongside the lab's own reference column rather than relying purely on general figures.
| Parameter | Normal Range |
|---|---|
| Hemoglobin (Men) | 13.5–17.5 g/dL |
| Hemoglobin (Women) | 12.0–15.5 g/dL |
| RBC Count | 4.5–5.9 million/µL |
| WBC Count | 4,500–11,000 /µL |
| Platelet Count | 150,000–450,000 /µL |
| Hematocrit | 38–50% |
Values below the normal range for hemoglobin and hematocrit typically point toward anemia, while a raised white cell count often signals infection or inflammation, and a low platelet count can indicate an increased bleeding risk — your doctor will interpret the full picture together rather than any single number in isolation.
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Frequently Asked Questions
Do I need to fast before a CBC?
No, fasting is not required for a standard CBC. You can eat and drink normally before the test unless your doctor has also ordered a fasting test like blood glucose alongside it.
How long does it take to get CBC results?
Most labs process a CBC within a few hours, and same-day results are common. Emergency departments can often get results within 30–60 minutes.
What does a low platelet count on a CBC mean?
A low platelet count, called thrombocytopenia, can result from a viral infection, certain medications, an autoimmune condition, or a bone marrow problem. Your doctor will usually recommend a repeat test or additional workup to identify the cause.
Can a CBC detect cancer?
A CBC alone cannot diagnose cancer, but unusual patterns — such as a very high or very low white cell count, or abnormal-looking cells noted by the lab — can prompt your doctor to investigate further with additional tests like a peripheral blood smear or bone marrow biopsy.
What does a high WBC count mean?
Often infection or inflammation, but also stress, smoking, steroids and sometimes blood disorders. Your doctor interprets it with the differential.
What is a dangerous hemoglobin level?
Below about 7–8 g/dL usually needs urgent evaluation, but symptoms and cause matter.
Can a CBC detect cancer?
It can show clues of blood cancers such as leukaemia, but it cannot diagnose cancer by itself.
What is RDW?
It measures variation in red cell size, and is often raised in nutritional deficiency anaemia.
Do I need to fast for a CBC?
No.
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Medical Disclaimer: This page is for informational purposes only and does not constitute medical advice. Lab test results should always be interpreted by a qualified healthcare professional in the context of your clinical history. Do not self-diagnose or alter your treatment based on test results alone.
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