A hematologic examination is the microscopic examination of the cells of the blood or blood-forming tissues (especially bone marrow), looking for changes in the structure of and /or numbers of various types of blood cells, including immature cells.

Peripheral blood is circulating blood obtained from the extremities or from the circulatory system remote from the heart. One of the most frequently used procedures for obtaining blood for a complete blood count is the fingerstick method. Other procedures for obtaining specimens for hematologic examination include venipuncture, bone marrow aspiration, and bone marrow biopsy which will be discussed in detail later.

There are three main types of blood cells-erythrocytes, leukocytes, and thrombocytes (platelets)-all suspended in a fluid portion called plasma.