What is a complete blood count?
A complete blood count, or CBC, is a group of laboratory measurements that assesses the number and characteristics of the main types of blood cells. It usually includes red blood cells, white blood cells, platelets, hemoglobin, hematocrit, and red blood cell indices. If a CBC with differential is ordered, the laboratory also measures the main types of white blood cells separately.
A complete blood count, or CBC, is a group of laboratory measurements that assesses the number and characteristics of the main types of blood cells. It usually includes red blood cells, white blood cells, platelets, hemoglobin, hematocrit, and red blood cell indices. If a CBC with differential is ordered, the laboratory also measures the main types of white blood cells separately.
What does a complete blood count show?
A CBC provides an overview of the cellular composition of blood and can reveal changes associated with anemia, infection or inflammation, abnormal platelet counts, and other conditions. It is also used during routine checkups and to monitor an illness or treatment.
A CBC provides an overview of the cellular composition of blood and can reveal changes associated with anemia, infection or inflammation, abnormal platelet counts, and other conditions. It is also used during routine checkups and to monitor an illness or treatment.
A single abnormal CBC value does not establish a diagnosis. Results are interpreted together with other tests, symptoms, medical history, and the reason for testing.
| Group of values | What it assesses |
|---|---|
| Red blood cells, hemoglobin, hematocrit | Oxygen transport and the characteristics of red blood cells |
| MCV, MCH, MCHC, RDW | Red blood cell size and hemoglobin content |
| White blood cells and differential | Total white blood cell count and the distribution of white blood cell types |
| Platelets | The number of cells involved in blood clotting |
When is a complete blood count ordered?
A CBC may be ordered as part of a routine health assessment, to investigate symptoms, or to monitor a known condition. It helps identify changes in blood cell counts but cannot determine their cause without other clinical information.
A CBC may be ordered as part of a routine health assessment, to investigate symptoms, or to monitor a known condition. It helps identify changes in blood cell counts but cannot determine their cause without other clinical information.
| Situation | Why a CBC may be useful |
|---|---|
| Routine checkup or hospital admission | To obtain a general overview of blood cell counts |
| Weakness, fatigue, dizziness, shortness of breath, or pale skin | To assess hemoglobin, red blood cells, and possible anemia-related changes |
| Fever or signs of infection or inflammation | To assess white blood cells and, if ordered, the white blood cell differential |
| Unusual bruising, bleeding, or prolonged bleeding | To assess platelet count and other blood values |
| Chronic illness | To monitor changes over time |
| Treatment that may affect blood cells | To monitor safety and the body’s response to treatment |
How to prepare for a complete blood count
No special preparation is usually required for a CBC itself. If it is ordered together with blood chemistry, a lipid panel, or other tests, fasting may be required. Follow the instructions provided by your clinician or laboratory.
No special preparation is usually required for a CBC itself. If it is ordered together with blood chemistry, a lipid panel, or other tests, fasting may be required. Follow the instructions provided by your clinician or laboratory.
| Question | Recommendation |
|---|---|
| Do I need to fast? | Usually not for an isolated CBC. Fasting may be required for other tests collected at the same time |
| Can I drink water? | If fasting is required, plain water is usually allowed |
| What time should I take the test? | A CBC usually does not require a specific time. Follow the rules for any other tests ordered with it |
| What about medicines? | Tell your clinician or laboratory about all medicines and supplements. Do not stop them on your own |
| Can I exercise beforehand? | If you are fasting for a group of tests, avoid exercising during the fasting period and follow any additional laboratory instructions |
How the sample is collected
The sample is usually taken from a vein. The blood draw takes only a few minutes. If the CBC is ordered for a child or a different collection method is needed, the laboratory will provide separate instructions.
What is included in a complete blood count?
A CBC assesses the number and characteristics of red blood cells, white blood cells, and platelets. The exact panel varies by laboratory. A basic CBC may report only the total white blood cell count, while a CBC with differential reports the main white blood cell types separately.
A CBC assesses the number and characteristics of red blood cells, white blood cells, and platelets. The exact panel varies by laboratory. A basic CBC may report only the total white blood cell count, while a CBC with differential reports the main white blood cell types separately.
| Group | Common report abbreviations | What the values describe |
|---|---|---|
| Red blood cells and oxygen transport | RBC, HGB, HCT | Red blood cell count, hemoglobin level, and the proportion of blood made up of red blood cells |
| Red blood cell indices | MCV, MCH, MCHC, RDW | Average red blood cell size, hemoglobin content and concentration, and variation in cell size |
| White blood cells | WBC | Total white blood cell count |
| White blood cell differential | NEUT, LYMPH, MONO, EOS, BASO | The number or percentage of neutrophils, lymphocytes, monocytes, eosinophils, and basophils |
| Platelets | PLT; sometimes MPV, PDW, PCT | Platelet count and, depending on the laboratory, platelet size characteristics |
CBC and CBC with differential
A standard CBC measures the total white blood cell count. A CBC with differential also measures the five main types of white blood cells. They may be reported as absolute counts, percentages, or both. These formats should not be treated as interchangeable.
Is ESR included?
The erythrocyte sedimentation rate, or ESR, may be sold together with a CBC, but it is a separate test and is not a standard part of the CBC. Check whether ESR is included in the specific laboratory offer.
Adult complete blood count reference ranges
CBC reference ranges depend on the laboratory method, age, sex, pregnancy, and other factors. When reviewing your own result, use the limits printed on your laboratory report first. The ranges below are examples from one NHS laboratory service and do not replace the ranges used by your laboratory.
CBC reference ranges depend on the laboratory method, age, sex, pregnancy, and other factors. When reviewing your own result, use the limits printed on your laboratory report first. The ranges below are examples from one NHS laboratory service and do not replace the ranges used by your laboratory.
Example adult reference ranges
| Test | Men | Women | Units |
|---|---|---|---|
| Hemoglobin, HGB | 130–180 | 115–165 | g/L |
| Red blood cells, RBC | 4.50–6.50 | 3.80–5.80 | ×10¹²/L |
| Hematocrit, HCT | 0.40–0.54 | 0.37–0.47 | L/L |
| White blood cells, WBC | 3.6–11.0 | 3.6–11.0 | ×10⁹/L |
| Platelets, PLT | 140–400 | 140–400 | ×10⁹/L |
| MCV | 80–100 | 80–100 | fL |
| MCH | 27–32 | 27–32 | pg |
White blood cell differential: example absolute counts
| Test | Adults | Units |
|---|---|---|
| Neutrophils | 1.8–7.5 | ×10⁹/L |
| Lymphocytes | 1.0–4.0 | ×10⁹/L |
| Monocytes | 0.2–0.8 | ×10⁹/L |
| Eosinophils | 0.1–0.4 | ×10⁹/L |
| Basophils | 0.02–0.10 | ×10⁹/L |
Important points:
How to interpret a complete blood count
A CBC should not be read as a collection of isolated “good” or “bad” numbers. Start by checking the units and laboratory reference ranges, then assess red blood cells, white blood cells, and platelets together with their related indices.
A CBC should not be read as a collection of isolated “good” or “bad” numbers. Start by checking the units and laboratory reference ranges, then assess red blood cells, white blood cells, and platelets together with their related indices.
One abnormal value does not establish a diagnosis and may need to be confirmed with repeat testing or additional investigations.
Step-by-step approach
- Check the sex, age, units, and reference ranges shown on the report.
- Review hemoglobin, red blood cells, and hematocrit as one group.
- If they are abnormal, review MCV, MCH, MCHC, and RDW.
- Review the total white blood cell count together with the differential.
- Review platelets and, if reported, MPV and other platelet indices.
- Compare the result with previous tests performed under similar conditions.
- Consider symptoms, medicines, hydration, exercise, menstruation, and any current illness.
Common patterns
| Pattern | What it may suggest | What else is considered |
|---|---|---|
| Low HGB, RBC, or HCT | Anemia-related changes or blood loss | MCV, MCH, RDW, ferritin, vitamin B12, folate, and clinical information |
| Low HGB with low MCV | A microcytic pattern that often requires assessment of iron status | Ferritin, transferrin or TIBC, and transferrin saturation |
| Low HGB with high MCV | A macrocytic pattern | Vitamin B12, folate, medicines, liver tests, and other causes |
| High HGB, RBC, or HCT | Hemoconcentration or an increased red blood cell count | Hydration, altitude, smoking, lung conditions, and other factors |
| High WBC | A possible response to infection, inflammation, stress, medicines, or other processes | Differential count, symptoms, and repeat testing |
| Low WBC | Possible effects of medicines, viral illness, immune conditions, or bone marrow processes | Absolute neutrophil count, other blood cells, and medical history |
| High or low PLT | Changes in platelet production, use, or distribution | Repeat CBC, blood smear, inflammation, medicines, and the clinical situation |
How to read red blood cell indices
When a result needs medical attention
Discuss the result with a clinician if the abnormality is substantial, persists on repeat testing, occurs together with other abnormal values, or is accompanied by symptoms.
What additional tests may be ordered?
A CBC can show changes in blood cells but may not explain their cause. Depending on which values are abnormal, symptoms, and the clinical situation, additional tests may be ordered.
A CBC can show changes in blood cells but may not explain their cause. Depending on which values are abnormal, symptoms, and the clinical situation, additional tests may be ordered.
| CBC finding | Additional tests that may be used | Purpose |
|---|---|---|
| Low hemoglobin or abnormal MCV, MCH, or RDW | Ferritin, serum iron, transferrin or TIBC, transferrin saturation | To assess iron status and iron stores |
| Macrocytic changes | Vitamin B12, folate, and sometimes methylmalonic acid | To investigate possible vitamin B12 or folate deficiency |
| Unexplained anemia-related changes | Reticulocyte count and peripheral blood smear | To assess blood cell production and morphology |
| High white blood cells or abnormal differential | Repeat CBC, absolute differential counts, CRP, or other tests based on symptoms | To assess trends and possible inflammation |
| Low white blood cells or neutrophils | Repeat CBC, blood smear, and tests based on the clinical context | To confirm the result and investigate the cause |
| Platelet abnormalities | Repeat CBC, peripheral blood smear, and coagulation tests when indicated | To assess platelet count, morphology, and clotting |
How much does a complete blood count cost?
The price of a CBC depends on the city, laboratory, and test composition. The same general name may refer to a basic CBC, a CBC with differential, a package that includes ESR, or a test with manual microscopy.
The price of a CBC depends on the city, laboratory, and test composition. The same general name may refer to a basic CBC, a CBC with differential, a package that includes ESR, or a test with manual microscopy.
Before comparing prices, check both the included values and any mandatory blood collection fee.
| Feature | What to check |
|---|---|
| Test composition | Basic CBC or CBC with differential |
| White blood cell differential | Included or not; automated or manual if specified |
| ESR | Included or charged separately |
| Blood smear microscopy | Automated, performed only when flagged, or included in the package |
| Number of reported values | Useful information, but not an automatic measure of test quality |
| Blood collection fee | Add it to the test price |
| Total price | Test price plus all mandatory fees |
| Turnaround time | The time stated by the laboratory |
Select your city to compare current laboratory offers and total prices.
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Frequently asked questions
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Authorship, sources, and limitations
This material explains the laboratory test, preparation, and result interpretation principles. For your own report, prioritize the exact test name, units, and reference ranges printed by your laboratory.
- MedlinePlus — Complete Blood Count (CBC)
- MedlinePlus — Blood Differential
- MedlinePlus — Red Blood Cell Indices
- MedlinePlus — White Blood Count
- MedlinePlus — Fasting for a Blood Test
- Gloucestershire Hospitals NHS — Haematology Reference Ranges
This material and Vitametria automated explanation are informational only and are not a diagnosis, medical opinion, or treatment recommendation.
Prices, panel composition, turnaround times, and promotional terms may change. Verify current details before payment.