What is a CBC test used for?

A complete blood count is a routine screening test that may help evaluate overall health and detect a wide range of conditions, including infection, anemia, and certain blood disorders.

Do I need to fast before a CBC?

Fasting is not usually required for a CBC. Always follow the specific instructions provided by your laboratory or clinician.

Understanding Your CBC (Complete Blood Count) Report

A plain-language guide to the CBC test — what each value measures, common reference ranges, and what abnormal results may indicate.

A complete blood count (CBC) is one of the most commonly ordered blood tests. It measures several components of your blood and may give your clinician a broad view of your overall health.

What a CBC measures

A standard CBC reports values across three main cell lines:

Red blood cells (RBC) — carry oxygen from the lungs to the rest of the body.
White blood cells (WBC) — part of the immune system; help fight infection.
Platelets — small cell fragments that help blood clot.

Within these, the report typically includes hemoglobin, hematocrit, MCV, MCH, MCHC, RDW, a WBC differential, and platelet count.

Common reference ranges

Reference ranges may vary between laboratories. The values below are general adult ranges and should not replace the ranges printed on your own report.

Hemoglobin: 13.5–17.5 g/dL (male), 12.0–15.5 g/dL (female)
WBC: 4,000–11,000 /µL
Platelets: 150,000–450,000 /µL

What abnormal values may indicate

Low hemoglobin may indicate anemia, which can have many causes. A high WBC count may indicate infection or inflammation, while a low WBC count may warrant further evaluation. Platelet abnormalities may relate to clotting, bleeding tendency, or marrow function.

These are general patterns only — interpretation should always be done with a qualified healthcare professional who has access to your full clinical picture.

When to discuss results with your doctor

If any value is flagged outside the reference range — particularly hemoglobin, WBC, or platelets — it is worth raising it with your clinician, even if you feel well.