Complete Blood count (CBC) A complete blood count (CBC) is a blood test used to evaluate your overall health and detect a wide range of disorders, including anemia, infection and leukemia. A complete blood count test measures several components and features of your blood, including: Red blood cells, which carry oxygen White blood cells, which fight infection Hemoglobin, the oxygen-carrying protein in red blood cells Hematocrit, the proportion of red blood cells to the fluid component, or plasma, in your blood Platelets, which help with blood clotting Abnormal increases or decreases in cell counts as revealed in a complete blood count may indicate that you have an underlying medical condition that calls for further evaluation.