A blood sample is taken and placed in a test tube containing an anticoagulant to stop it from clotting. It is then transported to a laboratory.

The process is generally done using automated equipment. The blood is well mixed and placed on a special rack on the analyzer. This instrument has many different components to analyze different elements in the blood. The cell counting component counts the numbers of red and white blood cells and platelets. The results are printed out or sent to a computer for review by a technician.

Because an automated cell counter samples and counts so many cells, the results are very precise. However, certain abnormal cells in the blood may be identified incorrectly. To be sure the results are correct, a technician reviews the blood smear on a slide and identifies any abnormal cells or blood parasites present.

In addition to counting, measuring, and analyzing red blood cells, white blood cells, and platelets, automated blood analyzers also measure the average size and the amount of hemoglobin in red blood cells. This information can be helpful when trying to identify the cause of an anemia.