ANNOTATION - TOTAL AND DIFFERENTIAL LEUKOCYTE COUNT

Two main problems with differential leukocyte counting are the difficulty of obtaining an even distribution of leukocytes in the film and the random error in estimating the proportion of the various cell types. The differential leukocyte count is generally used only to calculate the absolute numbers of various leukocytes. The errors in the estimates of the absolute numbers include the errors in the differential count and the errors in the WBC [total leukocyte count]. Many more cells can be counted when the leukocytes are in suspension; the Hemalog D (Technicon Corporation), for example, performs a differential count on 104 cells. Some simple techniques were devised for automating the differential leukocyte count. One such system differentiates leukocytes on the basis of their volumes and requires only pulse height analysis circuits connected to a Coulter Counter. When measuring normal values it is important to consider variations between different subjects as well as variations within each subject. Hematological values are influenced by age, sex, race, pregnancy, smoking and oral contraceptives. Minor infections, allergies and exercise can also affect the leukocyte count and so do diurnal and menstrual fluctuations.