CBC Explained: What the Complete Blood Count Actually Tells You
The CBC is the most-ordered blood test in the world. Here is how to read yours line by line.
The red cell line: oxygen delivery
Hemoglobin (Hgb) is the pigment that carries oxygen; hematocrit (Hct) is the proportion of blood volume that is red cells; RBC is the raw count. Low values suggest anemia; high values can suggest dehydration, smoking, or (rarely) a bone marrow disorder.
The indices matter. MCV (mean corpuscular volume) classifies anemia into microcytic (iron deficiency, thalassemia), normocytic (chronic disease, acute blood loss), or macrocytic (B12/folate deficiency, thyroid, alcohol). MCH and MCHC add detail on hemoglobin content per cell.
RDW (red cell distribution width) measures how variable red cell size is. An elevated RDW often appears before hemoglobin drops — a useful early clue.
The white cell line: immunity
Total WBC and the differential (neutrophils, lymphocytes, monocytes, eosinophils, basophils) tell you about infection, inflammation, and allergic response. A high neutrophil count typically suggests bacterial infection or acute stress; high lymphocytes often suggest viral infection; eosinophils rise with allergy or parasitic disease.
Persistent, unexplained shifts warrant investigation — not every elevated WBC is an infection.
Platelets: clotting and bleeding
Platelets (Plt) form the initial clot at a bleeding site. Low platelets (thrombocytopenia) can raise bleeding risk; high platelets can raise clotting risk or reflect inflammation or iron deficiency. A single mildly abnormal platelet count is usually repeated before further workup.
Order a CBC through a private draw
Ready to book? Reserve a private blood collection appointment on our Book Blood Collection page, or request a private requisition through blood test prescription.
Frequently asked questions
Do I need to fast for a CBC?+
No — a CBC does not require fasting.
How often should a healthy adult repeat a CBC?+
Once a year as part of an annual assessment is reasonable; sooner if you have symptoms or a chronic condition being monitored.