Complete Blood Count (CBC) Test: What It Measures and Why It Matters

Written by Bonnie Green on June 19, 2025

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The Complete Blood Count — better known as the CBC test — is one of the most ordered blood tests in modern medicine. It’s like a health dashboard, offering a detailed snapshot of your body’s cellular activity. Whether you’re feeling fatigued, managing a chronic condition, or simply doing a routine health check, a CBC is often the first test your provider will recommend.

But what exactly does it test for? And what can the numbers really tell you?

Let’s break it down.

What Is a CBC Test?

A Complete Blood Count evaluates the three main types of blood cells — red blood cells (RBCs), white blood cells (WBCs), and platelets — along with other key markers that help detect a range of conditions, from infection and inflammation to anemia and bone marrow issues.

Here’s what it typically includes:

🔴 Red Blood Cells (RBCs)

RBCs carry oxygen from your lungs to your tissues and remove carbon dioxide. Abnormal levels may indicate anemia, dehydration, or even heart disease.

🧬 Hemoglobin (Hgb)

Hemoglobin is the oxygen-carrying protein in red blood cells. Low levels suggest iron deficiency or chronic disease. High levels might result from smoking, living at high altitude, or dehydration.

🧪 Hematocrit (Hct)

This measures the percentage of your blood volume made up by red cells. It’s another tool for diagnosing anemia or polycythemia (too many red cells).

⚪ White Blood Cells (WBCs)

WBCs are part of your immune system. Elevated counts can indicate infection, inflammation, or even leukemia. Low counts may suggest autoimmune disorders, bone marrow issues, or the effect of certain medications.

🟣 Platelets

These are the blood’s clotting cells. Too few platelets may increase bleeding risk, while too many could lead to clots or indicate inflammation or cancer.

Why Would You Need a CBC?

The CBC is incredibly versatile. It’s ordered for a wide range of reasons, such as:

Routine check-ups to monitor overall health
Diagnosing symptoms like fatigue, dizziness, weakness, fever, or inflammation
Monitoring medical conditions, such as autoimmune diseases, infections, and cancers
Tracking the effects of chemotherapy or medications
Evaluating surgical readiness or recovery

What Do CBC Results Reveal?

The CBC doesn’t give a diagnosis outright — but it often signals where attention is needed. Here are some examples of what your results may point toward:

Low hemoglobin or hematocrit → Iron deficiency, blood loss, kidney disease
High WBC count → Infection, inflammation, stress, leukemia
Low WBC count → Autoimmune disease, bone marrow suppression, viral infections
Low platelets → Risk of excessive bleeding, bone marrow issues
High platelets → Inflammation, recent trauma, cancer

Doctors will often correlate CBC results with symptoms, history, and further tests to pinpoint the issue.

What to Expect During the Test

The CBC is one of the simplest and fastest lab tests to perform:

Fasting is not required in most cases (unless ordered with other tests like a lipid panel).
Blood is usually drawn from a vein in your arm.
The entire process takes just a few minutes.

Results typically return within 24 hours, sometimes faster.

How Much Does a CBC Test Cost?

Here’s where many people are surprised: the same CBC test can cost $12 at one provider and $80 at another — even though both use the same lab to process the sample.

Why such a price difference?

It often comes down to who you’re buying it through, whether it’s bundled with other tests, or if you’re using a direct-to-consumer lab versus a clinic or hospital.

At RateMyLab.com, we help you compare real-time pricing for CBC and other tests from top lab networks like Quest and LabCorp, across multiple platforms — so you don’t overpay for something routine.

Final Thoughts

Think of the CBC as the foundation of your health data — simple, affordable, and highly informative.

Whether you’re proactively monitoring your well-being or investigating symptoms, a CBC gives you and your doctor a baseline to work from. And now that you can shop around for lab tests, there’s no reason not to get this test when needed — without the sticker shock.

👉 Check current CBC prices near you on RateMyLab.com — and take charge of your health, one test at a time.