A Complete Blood Count (CBC) measures the cells in your blood: red cells that carry oxygen, white cells that fight infection, and platelets that help you clot. It's part of almost every annual physical and is often the first test ordered when you feel tired, run down, or are fighting an illness.
Your doctor may order a CBC to screen for anemia, look for signs of infection, monitor a known condition, or check how a medication is affecting your blood. A CBC with differential (CPT 85025) also breaks down the types of white blood cells, while a CBC without differential (CPT 85027) does not.
CBC reference ranges (US standard)
These ranges are aligned with Quest Diagnostics and LabCorp. Your own report prints the exact range your lab used — always defer to that range, since methods differ slightly between labs.
| Parameter | Normal Range | What it measures |
|---|---|---|
| Hemoglobin (Hgb) | Men 13.5–17.5 g/dL · Women 12.0–15.5 g/dL | Oxygen-carrying protein in red cells |
| Hematocrit (Hct) | Men 41–53% · Women 36–46% | Percentage of blood made of red cells |
| WBC (White Blood Cells) | 4,500–11,000 /µL | Infection-fighting cells |
| Platelets (PLT) | 150,000–400,000 /µL | Clotting cells |
| MCV | 80–100 fL | Average size of red blood cells |
| Neutrophils | 50–70% | First-responder infection cells |
| Lymphocytes | 20–40% | Viral-fighting immune cells |
What an abnormal CBC means
Low hemoglobin
The most common cause in US adults is iron deficiency, which affects roughly 10 million Americans. Other causes include B12 or folate deficiency, chronic disease, kidney disease, and blood loss — including from long-term NSAID use (ibuprofen, aspirin), which is very common in the US.
High white blood cell count (leukocytosis)
This is one of the most-searched lab results in the US. The most common cause is a bacterial infection (UTI, pneumonia, skin infection). Stress, intense exercise, corticosteroids like prednisone, smoking, and obesity also raise WBC. Leukemia is a rare cause — a high WBC alone is far more likely to be infection than cancer.
Low platelets (thrombocytopenia)
Causes include immune thrombocytopenic purpura (ITP), certain medications, heavy alcohol use, and viral infections. A platelet count under 50,000 means avoiding elective procedures; under 20,000 carries a spontaneous bleeding risk.