Chapter 2: Examination of Blood Cells

Daniel H. Ryan

INTRODUCTION

SUMMARY

Determining a patient’s blood cell counts and examining the appearance of cells on a blood film is central to the diagnosis of blood cell diseases and can give important information about numerous other degenerative, inflammatory, and neoplastic diseases that are reflected in quantitative or qualitative changes of blood cells. The quantity and quality of blood cells reflects the aggregate function of the major blood forming tissue, the marrow, and is thus an essential component of diagnosis and followup of primary hematological disorders. The decision to perform a marrow examination, and the types of special studies required, follow from a careful analysis of blood cells. Currently available automated blood cell analyzers continue to evolve and are the mainstay of blood cell counting, providing an increasing array of novel quantitative parameters, and flagging of abnormal samples that need manual microscopic review. The blood provides a unique example of a tissue that can be readily analyzed with a degree of quantitative detail unavailable in any other organ system.

The blood is examined so as to answer these questions: Is the marrow producing appropriate numbers of mature cells in the major hematopoietic lineages? Is the development of each hematopoietic lineage qualitatively normal? Are there abnormal (e.g., leukemia or lymphoma) cells in the blood? Quantitative measures available from automated cell counters are reliable and provide a rapid and cost-effective way to screen for primary or secondary disturbances of hematopoiesis. Light microscopic observation of the blood film is essential to confirm certain quantitative results and to investigate qualitatively abnormal differentiation of the hematopoietic lineages. Based on examination of the blood, the physician is directed toward a more focused assessment of marrow function or to systemic disorders that secondarily involve the hematopoietic system.

The complete blood count is a necessary part of the diagnostic evaluation in a broad variety of clinical conditions. Similarly, the leukocyte differential count and examination of the blood film, in spite of limitations as a screening test for occult disease, is important in initial 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 “qualitative” become quantitative as technology advances.

Acronyms and Abbreviations:

CHr, reticulocyte-specific hemoglobin content; EDTA, ethylenediaminetetraacetic acid; fl, femtoliter; FRC, fragmented red cell counts; Hct, hematocrit; HYPO%, percentages of red cells falling below a cutoff for hemoglobin concentration; %HypoHe, percentages of red cells falling below a cutoff for hemoglobin content; Ig, immunoglobulin; MCH, mean cell hemoglobin; MCHC, mean cell hemoglobin concentration; MCV, mean cell volume; MPV, mean platelet volume; NHANES, National Health and Nutrition Examination Survey; NK, natural killer; PDW, platelet volume distribution width; RBC, red blood cell; RDW, red cell distribution width; RET-He, reticulocyte-specific hemoglobin content.