Identify the various formed elements in the peripheral blood smear: erythrocytes, leukocytes, and platelets. Using your atlas, identify the different types of white blood cell (neutrophil, eosinophil, basophil, and monocyte). Know the general function of each.

Estimate the size of the various cells in micrometers using the diameter of the neighboring erythrocytes as the basis of comparision. Normal, undisturbed, adult human erythrocytes will average about 7.7 mm in diameter, with only small individual variations. Note variability in the size of monocytes and lymphocytes. Also note the nuclear shape and the variation in the nuclear / cytoplasmic ratio within these two forms.

If basophils are not found in your slide, observe examples of this cell type found by others during the lab period. Notify your lab instructor if you find a good example of a basophil. Neutrophils from female donors may show Barr bodies. These "drumsticks" represent the inactivated chromosome of the XX pair in females.

This slide is similar to those prepared for a complete blood cell count (CBC) with differential. A differential count estimates the percentages of the various white blood cells and compares this to the normal ratio of leukocytes. An alteration in WBC distribution often is caused by disease processes and has significant diagnostic value.

For example, an increase in the neutrophil count is suggestive of a bacterial infection. Decreased neutrophils (caused by leukemias or by chemotherapy) puts the individual at risk for certain opportunitic infections. A decrease in platelet count may be caused by excess platelet consumption (i.e., excessive clotting or platelet lysis triggered by autoantibodies) or by decreased platelet production in the bone marrow. Blood cell neoplasms such as leukemias cause an increased number of immature abnormal lymphocytes in peripheral blood.

NORMAL PERCENTAGES OF HUMAN BLOOD CELLS IN PERIPHERAL BLOOD

References: Gartner, p. 85, Fig. 1 - 6 Ross, p. 202, 211 - 213 Wheater, pp. 43 - 53; chart p. 60 DiFiore, pp.63 - 67, Fig. 5-1 - 5-7