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CHAPTER 2 evaluation in a broad variety of clinical conditions. Similarly, the leu-
The complete blood count is a necessary part of the diagnostic
EXAMINATION OF kocyte differential count and examination of the blood film, in spite of
limitations as a screening test for occult disease, is important in initial
BLOOD CELLS consideration of the differential diagnosis in most ill patients. Although
quantitative and qualitative (morphologic) examination of the cells
of the blood are considered separately in this chapter, the distinction
between these two is not absolute, and measures once considered “qual-
Daniel H. Ryan itative” become quantitative as technology advances.

QUANTITATIVE MEASURES OF CELLS IN
SUMMARY THE BLOOD

Determining a patient’s blood cell counts and examining the appearance of PRINCIPLES OF AUTOMATED BLOOD CELL
cells on a blood film is central to the diagnosis of blood cell diseases and can
give important information about numerous other degenerative, inflamma- ANALYSIS
tory, and neoplastic diseases that are reflected in quantitative or qualitative Automated blood cell analysis is the cornerstone of the modern hema-
changes of blood cells. The quantity and quality of blood cells reflects the tology laboratory, allowing rapid, cost-effective, and accurate analysis
aggregate function of the major blood forming tissue, the marrow, and is thus of the cells of the blood, including new parameters with diagnostic util-
an essential component of diagnosis and followup of primary hematological ity. The morphologic and functional complexity of blood cells requires
disorders. The decision to perform a marrow examination, and the types of direct microscopic examination of a stained blood film by a trained
observer. However, it is possible to use automated techniques to analyze
special studies required, follow from a careful analysis of blood cells. Currently and report on the majority of samples, using defined criteria (“flags”)
available automated blood cell analyzers continue to evolve and are the main- to select those that need further microscopic review. Automated hema-
stay of blood cell counting, providing an increasing array of novel quantitative tology analyzers typically incorporate multiple proprietary software
parameters, and flagging of abnormal samples that need manual microscopic flags based on acceptability criteria related to pattern recognition in the
review. The blood provides a unique example of a tissue that can be readily multiparameter displays or comparison of different detection modes for
analyzed with a degree of quantitative detail unavailable in any other organ the same cell type. These are frequently updated in software or when
system. new models are introduced to improve sensitivity and specificity. In this
way, instruments identify samples that contain cells or abnormalities the
instrument cannot definitively identify, so that a skilled morphologist
can visually evaluate that specimen. Some of these flags can be adjusted
or suppressed by the user to achieve an appropriate balance that mini-
INTRODUCTION mizes both false positives and false negatives. The optimum balance is
dependent on the patient population examined. Guidelines for manual
The blood is examined so as to answer these questions: Is the marrow smear review based on comparative data have been published, based
producing appropriate numbers of mature cells in the major hemato- on instruments then in common use. Protocols for evaluating and
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poietic lineages? Is the development of each hematopoietic lineage adjusting flagging criteria within an individual laboratory have been
qualitatively normal? Are there abnormal (e.g., leukemia or lymphoma) described. Manual review may consist of a scan of the blood film, a
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cells in the blood? Quantitative measures available from automated more detailed blood film examination including leukocyte differential
cell counters are reliable and provide a rapid and cost-effective way to count, or a physician’s review, based on laboratory defined criteria. The
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screen for primary or secondary disturbances of hematopoiesis. Light proportion of samples requiring manual blood film review differs among
microscopic observation of the blood film is essential to confirm certain instruments and the type of patient population tested. Studies show a
quantitative results and to investigate qualitatively abnormal differenti- 10 to 30 percent manual review rate, with a false negative rate (i.e.,
4–6
ation of the hematopoietic lineages. Based on examination of the blood, abnormal samples that were not flagged for review) varying from
the physician is directed toward a more focused assessment of marrow approximately 3 percent to 10–14 percent. Most of the false nega-
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function or to systemic disorders that secondarily involve the hemato- tives with current instrumentation are related to red cell and platelet
poietic system.
morphology with relatively limited diagnostic significance. Contin-
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ued improvement in methodology and increased sophistication of data
analysis will result in further reduction of unnecessary manual smear
reviews. Depending on workload and space considerations, laboratories
Acronyms and Abbreviations: CHr, reticulocyte-specific hemoglobin content; may choose to link automated hematology analyzers with automated
EDTA, ethylenediaminetetraacetic acid; fl, femtoliter; FRC, fragmented red cell blood film preparation and automated image analyzers to facilitate man-
counts; Hct, hematocrit; HYPO%, percentages of red cells falling below a cutoff for ual morphologic review of cells by traditional light microscopy or online
hemoglobin concentration; %HypoHe, percentages of red cells falling below a cutoff review of digitized images. These instruments can provide a provisional
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for hemoglobin content; Ig, immunoglobulin; MCH, mean cell hemoglobin; MCHC, differential count with good accuracy, although typically final classifi-
8
mean cell hemoglobin concentration; MCV, mean cell volume; MPV, mean platelet cation of problematic cells is performed by a technologist or physician.
volume; NHANES, National Health and Nutrition Examination Survey; NK, natural The characteristics of automated hematology analyzer systems
killer; PDW, platelet volume distribution width; RBC, red blood cell; RDW, red cell have been reviewed. A detailed description of individual instruments
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distribution width; RET-He, reticulocyte-specific hemoglobin content. is beyond the scope of this chapter, but the general principles employed
by state-of-the-art instrumentation are summarized below. The major

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