The complete blood count, or CBC, is the most commonly ordered blood test in the world. It measures the three main types of cells in your blood and is used to screen for anemia, infection, clotting problems and many other conditions. Here is what each part means.
Red blood cells and hemoglobin
Hemoglobin is the protein that carries oxygen. When it is low you may have anemia, which can cause fatigue and shortness of breath. Hematocrit and the red blood cell count move in the same direction as hemoglobin.
Red cell indices: MCV, MCH, RDW
These describe the size and content of your red cells and help find the cause of anemia. A low MCV points toward iron deficiency or thalassemia, while a high MCV suggests B12 or folate deficiency. RDW measures how varied your cell sizes are.
White blood cells
The white blood cell count reflects your immune activity. It rises with infection and inflammation. The differential breaks it down into neutrophils (bacterial defense), lymphocytes (viral defense), monocytes and eosinophils (often raised in allergy or parasites).
Platelets
Platelets help your blood clot. A very low count raises bleeding risk; a high count can occur with inflammation or, rarely, a bone marrow disorder.
How to read a CBC sensibly
One mildly out-of-range value on a CBC is common and often harmless. What matters is the pattern — for example, low hemoglobin with a low MCV strongly suggests iron deficiency. Trends over time are more meaningful than a single snapshot.
You don't have to interpret a single number alone. Upload your full lab report and Lab Lens will explain every value in plain English, or browse all our lab test guides.
This article is for general education only and is not medical advice. Reference ranges vary between laboratories — always read your result against the range on your own report and discuss it with your doctor.