CBC

A Complete Blood Count (CBC) is one of the most frequently ordered blood tests in medicine, giving your doctor a detailed snapshot of the three main cell types circulating in your blood: red blood cells, white blood cells, and platelets.

The test measures hemoglobin (the oxygen-carrying protein in red cells), hematocrit (the proportion of blood made up of red cells), red and white cell counts, and a platelet count, along with several derived indices like MCV and MCH that describe the size and hemoglobin content of individual red cells.

Because it touches on so many body systems at once — oxygen transport, immune defense, and clotting — a CBC is used both as a routine screening tool during annual checkups and as a targeted diagnostic test when a doctor suspects anemia, infection, inflammation, or a blood disorder.

It's quick, requires only a small venous blood sample, and results are typically available the same day, which is why it's often the very first test ordered when a patient reports vague symptoms like fatigue or unexplained bruising.