Peripheral blood film review. The demise of the eyecount leukocyte differential.

The automated hematology analyzer with CBC and differential results has replaced the traditional manual or individual assay methods for hematologic parameters and the eyecount leukocyte differential as the initial screening and detection system for hematologic abnormalities in modern hospitals and clinics. The traditional review of all automated hematology instrument results by preparation, staining, and microscopic examination of a blood film has disappeared in most institutions. The reasons are the more accurate detection of specimens with distributional or morphologic abnormalities by the instruments than by the traditional eyecount method. The opportunity for a clinician to request a microscopic examination of a blood film, whether or not it is flagged, must be preserved, because the clinician's knowledge of the patient's history, physical findings, and current or prior therapy may indicate review to discover an abnormality that may not have been apparent from the instrument results alone. There has also been a dramatic reduction of the numbers of medical technologists and technicians in medical laboratories. Automation of the CBC and differential counts has reduced the number of technologists needed for performance of these tests. But other factors have had a negative effect, such as the necessity to reduce costs. Consolidation of hematology and chemistry laboratories in core laboratories may produce savings in labor costs, but may also create problems of creating and maintaining areas of expertise, such as hematologic morphology, because of the cross-training required and the necessity of personnel to do all things. This article suggests and documents a number of measures that can be infinity stituted by the laboratory and by clinicians to reduce the number of eyecount differentials and blood film reviews that need to be performed. The first effort is to convince clinicians that valid data exist that confirm that a policy of allowing the laboratory to initiate blood film review based on findings of the CBC and automated differential is a more sensitive and accurate method of detecting patients with blood film abnormalities than routine blood film review of all specimens by technologists. Clinicians need to recognize that daily differential results or differentials at intervals of less than a week are not medically necessary in most patients. The laboratory, however, must provide opportunities for the clinician to request differentials at any time for specific medical reasons. The laboratory must establish the validity of screening criteria for detection of distribution and morphologic abnormalities of leukocytes by clinical correlation studies or adopt criteria established by laboratories with the same instrumentation and which have conducted clinical evaluations. A final observation on the eyecount differential is that it was the only way to identify cell types and their relative proportion for nearly 100 years. Cells were identified by their shape, intracellular structures, and staining characteristics. Many studies were able eventually to correlate some aspect of each cell type's function with their morphologic appearance. It has also been learned that the bone marrow is the source of production of most circulating cells and a great deal of the controls of cell production and release into the peripheral blood have been learned. But leukocytes have many functions, almost none of which are performed in the peripheral blood. The peripheral blood is mainly a conduit from the bone marrow to the tissues where the leukocytes perform their function in the case of the neutrophils and monocytes. It is mainly a recirculation and redistribution system for lymphocytes that usually receive their instructions from antigen processing cells in the tissues and allow these modified cells to home to sites where their functions occur. Cellular morphology and staining characteristics tell little about the maturation stage and functional capabilities of leukocytes. One cannot tell the difference between a band and a segmented neutrophil or whether a lymphocyte is a T or B cell on the conventional eyecount differential. One cannot tell the mature granulocyte of a patient with chronic myeloid leukemia from a normal mature neutrophil. Increasingly, techniques are being developed to identify better the maturation stages of cells and association with specific functional capabilities by flow cytometric techniques. The neoplastic nature of some normal-appearing leukocytes can be identified by techniques, such as fluorescent in situ hybridization. With the rapid advances in many approachs to understand the nature and functional capability of leukocytes, the eyecount differential with the traditional Romanowsky stain may be past the apogee of its ascent and beginning its trip into history along with the hemocytometer counting chamber and the Sahli pipet. The development and implementation of new laboratory cornerstone techniques for diagnosis of hematologic disease are eagerly awaited. On the other hand, the red cells and platelets exist to function in the peripheral blood. More emphasis is needed in the development of automated methods of determining the nature and functional capabilities of these true blood cells as part of the CBC.