Complete Blood Count (CBC)

A fundamental blood test that provides key insights into immune function, oxygen transport, and overall health

Complete Blood Count (CBC)

Table of contents

Basic data

A Complete Blood Count (CBC) is a routine diagnostic test that evaluates the levels of various cells in your blood, including red blood cells, white blood cells, and platelets. It helps assess general health and detect a wide range of disorders, such as infections, anemia, and hematological abnormalities.

This test is widely used as a first-line health screening, often included in annual checkups or pre-treatment evaluations. It offers a quick, cost-effective snapshot of systemic health, immune activity, and potential red flags requiring further investigation.

Category: Lab blood panel

Level: Beginner

Usefulness: High

Level

Beginner

The CBC is a basic yet essential diagnostic test suitable for most individuals as part of regular health monitoring. Its interpretation is relatively straightforward, and it often serves as a gateway to deeper diagnostics when abnormalities are detected.

Usefulness

High

The CBC is a versatile and widely used test offering multiple insights into immune function, oxygen delivery, and potential systemic inflammation or infection.
Detects anemia and red blood cell disorders

Measures hemoglobin, hematocrit, and red blood cell indices to identify various forms of anemia or other red blood cell abnormalities.

Evaluates immune system status

White blood cell count and differential help detect infections, inflammation, and immune system imbalances.

Assesses clotting and platelet function

Platelet count and related metrics provide clues about clotting ability or potential bleeding disorders.

How it works

A small sample of blood is drawn, usually from a vein in your arm, and analyzed by automated machines that count and classify blood cells.
Blood collection

A healthcare professional draws blood into a tube containing an anticoagulant to prevent clotting.

Automated analysis

The sample is analyzed by hematology analyzers that count and characterize cells by size, shape, and quantity.

Measures

The CBC includes several key metrics grouped into red blood cell, white blood cell, and platelet parameters.
Hemoglobin (Hb) and Hematocrit (Hct)

Indicate oxygen-carrying capacity and help diagnose anemia or dehydration.

White Blood Cell (WBC) count and differential

Evaluate immune system status and detect signs of infection or inflammation.

Platelet count (PLT)

Assesses clotting potential and platelet-related disorders.

Mean corpuscular volume (MCV), MCH, MCHC

Provide insight into red blood cell size and hemoglobin content, aiding anemia classification.

Reliability

CBC is a highly standardized and automated test with strong reliability, though results may vary slightly depending on physiological or pre-analytical conditions.
Repeatability

CBC results are typically consistent when samples are drawn and processed correctly, with minimal inter-lab variability.

Sensitivity to conditions

Factors like hydration, acute illness, altitude, or recent physical activity can transiently influence results.

Limitations

While CBC is valuable as a screening tool, it lacks specificity and often requires additional diagnostics to confirm or explain abnormal results.
Limited diagnostic precision

Abnormal values may indicate a problem but don’t always point to a specific diagnosis without further tests.

Influenced by transient states

Dehydration, recent infections, stress, or even exercise can affect results temporarily.

Frequency

Suggested cadence

For healthy individuals, once per year during an annual checkup is generally sufficient. More frequent monitoring may be warranted in specific clinical contexts.

Cost

Typical costs

The CBC is one of the most affordable lab tests, typically ranging from 20 to 80 PLN in Poland or $10 to $40 USD depending on the provider.

Availability

Where available

Available at virtually all medical laboratories, hospitals, and clinics worldwide. No referral is typically required in private healthcare.

Preparation

How to prepare

No special preparation is needed for a CBC. Fasting is not required unless the test is part of a larger blood panel.

Interpretation

Interpreting a CBC involves reviewing the levels and ratios of different cell types, often in the context of symptoms or additional lab data.
Focus on abnormal counts

Elevated or decreased WBCs, RBCs, or platelets can indicate infection, inflammation, anemia, or hematological disorders.

Differential patterns

The WBC differential can help distinguish between viral vs. bacterial infections or suggest allergic or autoimmune activity.

Alternatives

Reticulocyte count

Offers more detailed insight into bone marrow activity and red blood cell production.

Bone marrow biopsy

Used in specific cases where deeper investigation into blood cell abnormalities is needed.

FAQ

Do I need to fast before a CBC?

No, fasting is not required for a CBC alone. However, you may need to fast if it’s combined with other tests like lipid or glucose panels.

Can CBC detect cancer?

While CBC may show abnormalities suggestive of leukemia or lymphoma, it is not a definitive cancer test and requires follow-up diagnostics.