As we move forward into the 21st century, the field of diagnostic medical parasitology continues to see some dramatic changes, including newly recognized pathogens, changing endemicity of familiar pathogens, disease control challenges, geographic and climate changes that support the spread of parasitic disease, new methodologies, expansion of diagnostic testing, and an ongoing review of the approach to and clinical relevance of this type of diagnostic testing on patient care within the managed care environment, as well as the world as a whole.

The third edition of the Practical Guide to Diagnostic Parasitology is organized to provide maximum help to the user, particularly from the bench use perspective. New aspects of the field have been addressed throughout, and many new figures and plates have been added, including extensive color images. All of the changes for this edition are based on the need for readers to update their information related to diagnostic medical parasitology and specifically issues involving laboratory techniques. With continued emphasis on regulatory requirements related to chemical disposal and the use of mercury compounds, laboratories are being required to develop skills using substitute fixatives that are prepared without the use of mercury‐based compounds. In most cases, organism identification is comparable; an example of a rare exception is one in which the number of organisms present is quite low. This is a prime example of a change where “different” has been acceptable and relevant, not necessarily “good” or “bad.” It is also important to remember the large number of variables relevant to diagnostic parasitology testing.

Section 1 of this new edition, on the philosophy and approach to diagnostic parasitology, has been expanded to include discussions on neglected tropical diseases, the impact of global climate change, population movements, potential outbreak testing, the development of laboratory test menus, and the risk management issues related to “stat” testing. The Section 2 discussion of organism classification and relevant tables has been expanded and updated to provide the user with current information related to changes in nomenclature and the overall importance of the various parasite categories to human infection.

In Section 3, expanded information on stool specimen fixatives and testing options has been provided. This information is valuable for any laboratory that is reviewing collection and testing options related to fixative compatibility with the routine ova and parasite examination, as well as fecal immunoassays and the newer molecular parasite panels. It is always important to check the literature from the relevant company to confirm the FDA status of any new product. The discussion on blood collection, including the pros and cons of current changes from finger‐stick blood to venipuncture, has been greatly enhanced, particularly related to potential problems with blood parasite morphology and lag time issues. Additional tables serve to summarize much of this new information.

New tables and information have been added to Sections 4 and 5, including a number of new algorithms. Section 6 is one of the most important sections in the book, with extensive revisions related to the most commonly asked questions regarding diagnostic parasitology methods. Additional techniques have been included (molecular test panels), as well as new information related to reporting results and the importance of report comments. This section’s “FAQ” format makes it easy for the reader to use the expanded information.

Section 7 has been greatly expanded, including the addition of extensive color figures. Figures and life cycle diagrams have also been expanded and updated. Section 8 presents information on potential problems with organism differentiation from one another and from possible artifacts. The section has been significantly expanded with new tables and image plates to illustrate these differences. Section 9 contains numerous tables and a set of identification keys that summarize identification aids and organism characteristics. As with earlier sections, the information is presented to assist the bench microbiologist with routine diagnostic testing methods.

Many laboratories are reviewing all microbiological services, and specific questions are being asked related to diagnostic parasitology options. Some of these questions include the following: what laboratories should be performing this type of testing, when should testing be performed, what tests should be performed, and what factors should be considered when developing test menus. There are also ongoing discussions related to the development of automated parasite panels and how the use of these panels could impact many of the routine procedures now in use.

Laboratories are also reviewing specimen collection options, particularly as they relate to their geographic area and types of patients serviced. This kind of analysis is beneficial to all concerned, not only in helping laboratories to understand the specimen collection options, but how they relate to test orders, diagnostic testing, and results impacting patient care.

With changes in collection, testing, reporting, and interpretation options, it is critical to remember that this information needs to be shared with the laboratory's client base, particularly if the test orders and results are to be used for the best‐quality patient care. Although there are many ways to approach diagnostic parasitology testing, it is mandatory that the laboratory and user both understand the pros and cons of the methods selected and the importance of test menu names, particularly in terms of procedure limitations and test name relevance for billing functions. The use of different approaches to parasitology diagnostic testing is acceptable; however, the benefits and drawbacks must be thoroughly understood by all participants. There may be legitimate reasons why different approaches are used by different laboratories; however, cost containment must not be the sole factor in selecting methods.

Another consideration is the fact that not all clinical laboratories will continue to perform diagnostic parasitology testing. This may be due to financial considerations, lack of skilled personnel, etc. With increased emphasis on cross‐trained individuals, the technical expertise required to identify these parasites by using routine microscopy may be lacking. Even with the use of molecular diagnostics, these tests are not capable of covering the entire spectrum of organisms that may be present as pathogens. However, as more of these newer automated molecular panels become commercially available, the use of nonmicroscopic methods will increase. Many laboratories now include both the ova and parasite examination and various fecal immunoassays on their routine test menus; on the basis of patient histories and symptoms, appropriate orders may focus on one or the other of these options. An important consideration in deciding whether to send out parasitology testing, or to maintain the testing in‐house, relates to stat testing (collection, processing, testing, reporting of thick and thin blood films, and the examination of cerebrospinal fluid and other specimens for the presence of free‐living amebae). These tests must be handled as stat; the time required from collection to reporting must be considered prior to moving these procedures off‐site or sending specimens to a reference laboratory.

Based on the many changes in clinical laboratories within the past few years and many years' experience with teaching and diagnostic bench work, it is my hope that the information contained in this third edition will provide valuable information for the user. This guide is not designed to serve as a diagnostic parasitology text or to contain all possible diagnostic test options, but to help the user make some sense of a field for which training has become almost nonexistent. I have included a section on commonly asked questions about diagnostic medical parasitology and hope that this discussion will be of practical value to the user; the answers to some of these questions are often difficult to find, even in a more comprehensive book. Again, let me emphasize that different approaches to laboratory work are not always “good” or “bad.” The key to success is making sure that both the laboratory and clients understand the pros and cons of each collection, testing, and reporting option and that educational information is provided for all clients on an ongoing basis. Two of the most important functions of the clinical laboratory in the future will be educational and consultative, particularly when laboratory services are within the microbiology area. The importance of well‐trained bench microbiologists cannot be underestimated.

A final point is that infectious diseases, particularly parasitic infections, play a huge role in the world's overall health and economy. As travel increases, we anticipate seeing many more people who will be infected with parasites that may not be endemic to the specific area where they live. Continued vector and disease control efforts will remain on the high‐priority list, especially when seen within the context of global health. It is hoped that parasitologists and microbiologists, including those who have diagnostic skills, will be available to support these global initiatives.