White blood cells count
White blood cells counts are performed by automated cell counters on blood samples appropriately diluted with a solution that lyses the erythrocytes(e.g., an acid or a detergent), but preserves white blood cells integrity. Manual counting of white blood cells is used only when the instrument reports a potential interference or the count is beyond instrument linearity limits. Manual counts are subject to much greater technical variation than automated counts because of technical and statistical factors.
False white blood cells counts
Automated white blood cells counts may be falsely elevated as a result of cryoglobulins or cryofibrinogen, clumped platelets or fibrin from an inadequately anticoagulated or mixed sample, ethylenediaminetetraacetic acid (EDTA)-induced platelet aggregation, nucleated red blood cells, or nonlysed red cells, and falsely decreased because of EDTA-induced neutrophil aggregation. This potential interference is very instrument dependent, and current analyzers use a variety of algorithms to minimize their effect and flag those rare samples in which accurate automated analysis cannot be performed. With respect to nucleated red cells, high end analyzers routinely and accurately quantify these cells with detection limits of 1 to 2 nucleated red cells per 100 white blood cells. Nucleated red cells are normally present in small numbers in neonatal blood, and are increased in a variety of hematopoietic disorders and conditions of severe hematopoietic stress.
White blood cells differential
white blood cells in the blood serve different functions and arise from different hematopoietic lineages, so it is important to evaluate each of the major white blood cells types separately. Modern automated instruments use multiple parameters to identify and enumerate the five major morphologic white blood cells types in blood: neutrophils, basophils, eosinophils, lymphocytes, and monocytes, as well as indicate the possible presence of immature or abnormal forms.
Normal white blood cells variation
The normal differential white blood cells count varies with age. polymorphonuclear neutrophils are predominant in the first few days after birth, but thereafter lymphocytes account for the majority of leukocytes.This pattern persists up to approximately 4 to 5 years of age, when the polymorphonuclear leukocyte again becomes the predominant cell and remains so throughout the rest of childhood and adult life. Chapter 8 discusses the leukocyte count in older persons. The leukocyte count may decrease slightly in older subjects be-cause of a fall in the lymphocyte count with age. The reference range for neutrophil counts is lower in Americans of African descent, and in African, Afro-Caribbean, and some Middle Eastern populations than in persons of European descent.