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The methods described in this book are predominantly the common ones found in clinical laboratories. Each method description provides an overview of the basic concept of the assay, minimizing the details, while including clinically important information and a comment on the expense of the test and the complexity of the assay in the laboratory.
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Each method also has a descriptor to reflect whether it is manual, semiautomated, or highly automated. A comment has been added if microscopy is involved, as this makes any technique highly manual. It should be noted that for some methods, there is an option for manual performance or for using some level of automation. There is usually greater automation in the larger clinical laboratories because larger laboratories are more likely to have the test volume and the financial resources to justify the automated option. The purchase of test reagents in large quantities also results in a lower purchase price. The term “semiautomated” indicates that there is a manual component associated with the use of an instrument that performs some steps of the analysis.
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The expense assessment attached to each assay described in this chapter is an approximation, listed as low, moderate, or high. The charge for the test set by the institution operating the laboratory is usually proportional to the expense of the reagents, supplies, and labor required to perform the test. On occasion, however, there is a great disparity between the actual expense to perform the test and the amount charged by the institution for the assay. With this in mind, the expense estimation provided for each method in this chapter is more closely related to the actual cost of reagents, supplies, and labor in the laboratory, with the understanding that the amount charged for the test should be in the same range of low, moderate, or high—but it is not always the case.
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The turnaround time for an assay is not provided because it is impossible to know all of the elements associated with the turnaround time for a test within an individual institution. Broadly speaking, the turnaround time is shorter for assays that are highly automated and less expensive, and longer for assays that are manual and highly expensive. It is important to understand that the turnaround time for an assay can be calculated using different starting points. For example, one starting point is the time a sample is collected. Another starting point is the time that a sample enters the laboratory. However, the most relevant starting time clinically, which predates the previous two starting times, is the time at which the physician actually orders the test. Similarly, there are different end points in the assessment of turnaround time. Most commonly, the end point is the time at which the result is reported by the laboratory into the laboratory information system. However, it is most important to know when the physician becomes aware of the result, because it is at that point that treatment may commence.
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Finally, it should be noted what methods are not presented in this chapter. There are a number of methods that have been used progressively less over time, and in many institutions these assays are no longer performed at all in the clinical laboratory. These are numerous and include, among many, the radioimmunoassay (RIA), immunoelectrophoresis, lipoprotein electrophoresis, and the bleeding time. A major effort was made to greatly expand the number of molecular genetic methods. These molecular genetic methods are described in this book. These are often highly complex, and the intention was to provide enough detail for the methods to be understood without making them confusing at the same time.