Biomedical subjects
Publications and source records attributed to G L Gulati.
Despite recent advances in the automation of clinical hematology laboratories, a careful microscopic examination of an appropriately prepared and stained blood smear continues to maintain its status as the most informative and useful diagnostic procedure, and offers a simple, reliable means of verifying results generated by automated analyzers. A systematic approach to a comprehensive evaluation of blood cells and related findings is described.
CBC traditionally stands for complete blood count. It represents a profile of tests rather than a single test, and over the years it has been given several names, including hemogram, Coulter profile, blood cell profile, and hematology profile. The number and type of tests included in the profile has also changed over time and among laboratories, depending primarily upon capabilities of the automated analyzers used to perform the profile test.
During the decade of the 1980s, a wealth of information accumulated concerning automation in hematology. Recent technological advances led the way to the development of blood cell analyzers capable of performing a ten-parameter (or greater) complete blood count and five-parameter (or greater) differential leukocyte count on a small amount of whole blood and in an accurate, efficient, and economical way. The authors summarize the available information concerning the data generated by these analyzers, the mechanisms involved in the data generation, and the clinical applications and usefulness or limitations of the so-called new complete blood count parameters and of the automated differential as it compares with the manual differential.
Today's automated hematology analyzers capable of performing a full CBC and a differential leukocyte count (DLC) on whole blood, particularly in a closed tube system, using cytochemistry or impedance-based flow cytometry technology coupled with laser light scattering, conductivity and/or differential cell lysis, are here to stay. Their need and popularity among at least the large, cost and quality-conscious clinical laboratories have been growing for the past few years and will continue to do so in the years ahead. The efficiency and reliability of several of these analyzers in performing complete CBCD (CBC and DLC) and in flagging significant abnormalities have been tested and found acceptable with the need to review a stained blood smear or perform a manual DLC to confirm or obtain additional information on selected cases.
Leukocytosis, mild anemia, thrombocytosis, and panhyperplasia in the marrow characterize the early stages of most of the CMPD, whereas extramedullary hematopoiesis (such as in the spleen or liver), peripheral cytopenias (anemia, leukopenia, or thrombocytopenia), and myelofibrosis, with or without osteosclerosis, reflect the changes seen in the later stages. Transitions among the different CMPD and termination in acute leukemia or marrow failure also are common. CML often is characterized by leukocytosis and the presence of the entire spectrum of granulocytes (mature and immature) in the blood and marrow, reduced LAP, hypercellularity with prominent granulocytic hyperplasia in the marrow, Ph chromosome, and bcr-abl gene rearrangement. Typical features of AMM include leukoerythroblastosis, teardrop poikilocytosis, anemia, increased or normal LAP, prominent megakaryocytic hyperplasia in the marrow, dyshematopoiesis, and hyperplastic or fibrotic/sclerotic marrow.
Bone marrow, a well-organized tissue located within the bone cavities, is richly innervated and highly vascularized but devoid of lymphatics. Structurally, it consists of two major cellular elements, the stromal cells (reticular cells--fibroblasts, endothelial cells, adipocytes, and so on) and the parenchymal cells (hematopoietic cells). Functionally, it serves as the primary site for hematopoiesis and as a major reticuloendothelial organ involved in immune responses (cellular and humoral) and removal of senescent and abnormal cells and particulate material. An uncommitted pluripotential hematopoietic stem cell, itself a product of the differentiation of mesenchymal cells of the yolk sac and capable of self-replication, undergoes proliferation and differentiation in an orderly manner, generating immature committed progenitors with uni-, bi-, or trilineage specificity. These committed progenitors also multiply and differentiate in a sequential fashion, ultimately producing mature cells that are released into the circulation. Under steady state conditions, the cell death/loss is balanced by cell production by virtue of regulatory mechanisms that apparently involve (1) cell-cell interaction between marrow cells and (2) production of humoral growth and/or inhibitory factors by stromal and parenchymal cells individually or in concert. Some of these regulators of hematopoiesis have been isolated, purified, molecularly cloned, and characterized. The availability of recombinant growth factors has stimulated clinical trials of these factors as therapeutic agents.
Proper evaluation of the bone marrow requires adequate sampling, appropriate specimen processing, sufficient clinical history, and review of representative blood smears and pertinent laboratory data. Aspiration and needle biopsy should be performed at the same time routinely. Aspirate smears, touch preparations from the biopsy, and sections from the aspirate and biopsy should be processed appropriately and examined in a systematic fashion to perform a comprehensive evaluation considered essential to arrive at or rule out a diagnosis, or as an adjunct in the management of patients, particularly those undergoing chemotherapy and/or radiotherapy.
A quality control (QC) protocol for hematology, as for other sections of the laboratory, should encompass both internal and external QC programs. The extent to which a hematology laboratory should be involved depends upon various factors, including availability of facilities, financial resources, range of tests, workload, the number of staff and their levels of training, and the overall organization of the laboratory. To ensure quality patient care, the intralaboratory QC program must include at least the minimal measures of monitoring and control at each step from collection of blood specimens, through the actual processing and analysis, to reporting of the results. The protocol should be written concisely and in simple language; the procedure manual should offer all of the pertinent information along with references; all concerned personnel should be well trained and competent; and adequate facilities and time should be available for the purpose of QC. Continuing education is also an integral part of an effective QC program. Three very important aspects of QC in hematology are calibration of automated instruments, monitoring of accuracy and precision of instruments and procedures, and verifying the reliability of test results. In the absence of a true primary reference/standard for calibration of instruments for the CBC, the most commonly performed hematologic test, the use of commercial calibrators is acceptable. A combination of commercial controls (three levels) and retained or fresh patient blood specimens is recommended for monitoring of accuracy and precision on a long- and short-term basis. Patient red-cell indices moving average data allow continuous monitoring of instrument performance and should be used as an adjunct to other QC approaches to detecting instrument calibration drift. Correlation of results of related parameters and careful review of blood films remain the two most important and widely used approaches to ensure reliability of results obtained from automated hematology instruments. Participation in an external QC program offers the most practical means of monitoring overall work performance in comparison with instrument, method, and/or reagent-based peer group data. A laboratory may choose to participate in one or more national and/or regional QC programs, depending upon the range of tests it performs and the requirements of accreditation and regulatory agencies. Most of the accreditation agencies require participation in programs covering at least all of the routinely or frequently performed tests and, if available, also in those for infrequently performed tests.(ABSTRACT TRUNCATED AT 400 WORDS)
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