Peripheral Blood Smear Examination

  • An examination at low power (10X ocular, 10x objective) is first performed to evaluate the quality of the smear, ascertain the approximate number of white blood cells and platelets, and to detect rouleaux formation, platelet clumps, and leukocyte clumps and other abnormalities visible at low magnification. An optimal area for evaluation at higher magnification is also chosen. This should be an intact portion of the smear free of preparation artifact where the red blood cells are separated by 1/3 to 1/2 of a cell diameter. The red blood cells should stain a pink color, while neutrophils show “crisp” features, with deep blue-purple nuclear material and lilac to pinkish to violet cytoplasmic granules. Optimal preparation and staining of the peripheral blood smear is critical for morphologic examination; an inadequate smear should not be examined.
  • Following low power examination of a peripheral blood smear, the 50X or 100X objective of the microscope is selected (500X or 1000X total magnification when using a 10x ocular) and the area of morphology is examined in a consistent scanning pattern (Fig 3) to avoid counting the same cell(s) twice. A differential count of at least 100 white blood cells (200, 500, or 1000 is even better) is performed, and any abnormal morphology of RBCs, WBCs, and platelets observed during the differential count is recorded. Each morphologic abnormality observed should be quantitated (“graded”) separately as to severity (“slight to marked” or “1+ to 4+”). Medical technologists are well trained in the reproducible quantitation of morphologic abnormalities .
  • A fairly accurate estimate of the white blood cell count (cells/mL) can be obtained by counting the total number of leukocytes in ten 500X microscopic fields, dividing the total by 10, and multiplying by 3000. These estimates should approximate that obtained by the cell analyzer. If the estimate does not match the automated cell count, obtain the original blood specimen, confirm patient identity, repeat the automated analysis, and prepare a new smear.

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