Leukocytes Essays - Biology, Medicine, Anatomy, Cell Biology

Leukocytes Leukocytes and the leukocyte differential count To consider the leukocytes together as a group is something of a granfalloon, because each type of leukocyte has its own function and ontogeny semi-independent of the others. To measure the total leukocyte count and allow this term to mean anything to the doctor is a travesty, yet the wbc count has traditionally been considered a cardinal measurement in a routine laboratory workup for just about any condition. I cannot emphasize too much that to evaluate critically the hematologic status of a patient, one must consider the individual absolute counts of each of the leukocyte types rather than the total wbc count. For such a critical evaluation, the first step is to order a wbc count with differential. In many labs, the result will be reported as a relative differential, something like this: WBC 6000/?L segmented neutrophils 60% band neutrophils 2% lymphocytes 25% monocytes 8% eosinophils 3% basophils 2% Your first task is to multiply the wbc count by each of the percentages given for the cell types; this gives you an absolute differential. Now you're in business to get some idea as to the pathophysiologic status of the patient's blood and marrow. Thus, the illustration above becomes: WBC 6000/?L segmented neutrophils 3600/?L band neutrophils 120/?L lymphocytes 1500/?L monocytes 480/?L eosinophils 180/?L basophils 120/?L The total wbc count is invariably done using an automated method. Routinely, the differential count is done by hand (i.e., through the microscope) in smaller labs, and by automated methods in larger facilities. The automated methods are amazingly accurate, considering the fine distinctions that must often be made in discerning one type of leukocyte from the other. One manufacturer's machine can quite reliably pick out one leukemic blast cell in eight hundred or more leukocytes. Now we shall consider each of the leukocyte types individually. A. Neutrophils The most populous of the circulating white cells, they are also the most short lived in circulation. After production and release by the marrow, they only circulate for about eight hours before proceeding to the tissues (via diapedesis), where they live for about a week, if all goes well. They are produced as a response to acute body stress, whether from infection, infarction, trauma, emotional distress, or other noxious stimuli. When called to a site of injury, they phagocytose invaders and other undesirable substances and usually kill themselves in the act of doing in the bad guys. Normally, the circulating neutrophil series consists only of band neutrophils and segmented neutrophils, the latter being the most mature type. In stress situations (i.e., the acute phase reaction), earlier forms (usually no earlier than myelocytes) can be seen in the blood. This picture is called a left shift. The band count has been used as an indicator of acute stress. In practice, band counts tend to be less than reliable due to tremendous interobserver variability, even among seasoned medical technologists, in discriminating bands from segs by microscopy. Other morphologic clues to acute stress may be more helpful: in the acute phase reaction, any of the neutrophil forms may develop deep blue cytoplasmic granules, vacuoles, and vague blue cytoplasmic inclusions called D?hle bodies, which consist of aggregates of ribosomes and endoplasmic reticulum. All of these features are easily seen (except possibly the D?hle bodies), even by neophytes. The normal range for neutrophil (band + seg) count is 1160 - 8300 /?L for blacks, and 1700 - 8100 /?L for other groups. Keeping in mind the lower expected low-end value for blacks will save you much time (and patients much expense and pain) over the course of your career. Obesity and cigarette smoking are associated an increased neutrophil count. It is said that for each pack per day of cigarettes smoked, the granulocyte count may be expected to rise by 1000 /?L. B. Monocytes These large cells are actually more closely related to neutrophils than are the other granulocytes, the basophil and eosinophil. Monocytes and neutrophils share the same stem cell. Monocytes are to histiocytes (or macrophages) what Bruce Wayne is to Batman. They are produced by the marrow, circulate for five to eight days, and then enter the tissues where they are mysteriously transformed into histiocytes. Here they serve