Three Approaches to Creating an Essential Diagnostics List Free

The World Health Organization (WHO) established the Essential Medicines List (EML) in 1977 and the Essential Diagnostics List (EDL) in 2018.^1,2 It has been shown that medicines on national EMLs, as the EML has been adopted and adapted by many countries, have greater availability compared with countries that do not have a national EML,³ and it is expected the same will happen with diagnostic tests. However, where there is a list, there is always the question of priorities. Vertical programs of the WHO, which include tuberculosis, human immunodeficiency virus, hepatitis, malaria, and other communicable (infectious) diseases, have already prioritized diagnostics and medications for these diseases. But what about all remaining diseases? What is the best approach to develop an EDL that is most appropriate for health care? How will countries prioritize tests on the list? We will examine three approaches to addressing this question.

First Approach

Most Frequently Ordered Tests

In this issue of the American Journal of Clinical Pathology, Horton et al⁴ present a list of the top 25 tests ordered in five hospitals in three different continents. They show that these hospitals have strong similarities regarding the top five tests by volume and revenue, with the CBC being at the top of every hospital list, followed closely by a complete metabolic panel (CMP) that may or may not include liver function tests, and three hospitals have urinalysis as a top five test. Those tests that are different in the top five tests seem to relate to what is prevalent in their location and include thyroid function tests and tests for infectious diseases (eg, stool microscopy and sexually transmitted diseases). Of note, the authors of the publication acknowledge that tests for WHO vertical programs were not present in their list of tests likely due to these being performed outside their hospital or laboratory. Lists of diagnostic tests created using this approach are practical and applicable to most locations. However, the fact that a test is commonly ordered does not necessarily make it essential.

Second Approach

Use the EML Standard

A proposal to tie the EDL to the WHO EML was published in the New England Journal of Medicine and later expanded in Clinical Chemistry.^5,6 A list using this methodologic approach has the advantage of leveraging the well-established disease priorities of the EML to define the EDL. Another advantage is that there are medications at the end of the diagnostic process. One shortcoming of this approach is that there are conditions without recommended medications (eg, Ebola and other emerging diseases). Of interest, if one looks at the top 25 most frequently ordered tests in five hospitals as presented in this issue of the journal and the tests linking the EML to the EDL, there are many similarities: a CBC and a metabolic panel that includes creatinine and glucose are at the top. Both CBC and CMP are tied to diagnostics of a variety of conditions and are important to monitor disease progression and treatment toxicities.

Third Approach

Ask Laboratory Scientists

During the 2018 American Society for Clinical Pathology meeting in Baltimore, we presented a workshop entitled “What Would a Worldwide List of Essential Diagnostics Tests Look Like?” We had a total of 22 participants: 10 were technologists, seven had pathology or PhD credentialing, two were pathologist assistants, and two were trainees. We gave participants background information regarding health care and laboratory conditions in low- and middle-income countries as well as background on how the WHO created and updates the EML. Then we divided participants into four groups: (1) chemistry, immunology, and toxicology; (2) hematology and coagulation; (3) microbiology; and (4) molecular, immunohistochemistry, and cytogenetics. We asked each group to list 10 tests they thought would be most useful in their assigned areas for inclusion in a potential EDL. Once the groups had their lists, we asked them to share them. We ended the workshop presenting the recently developed WHO EDL.

Some of the issues discussed during the session of this third approach included the fact that instruments often provide a panel of results rather than a single result (eg, CBC). In addition, instruments of the same “type” may not offer the same menu. For example, the electrolyte component is separate from other chemistry measurements, and a particular institution may not necessarily have both. So when coming up with a list, all the components of a panel need to be defined as different tests, although they may be grouped in practice. Other discussions centered on the thought that once having a particular method, say plates for bacterial cultures or flow cytometry, one can test different specimens or distinguish different antigens. These discussions reflected many of the issues we discussed at length when creating the list that was published in Clinical Chemistry.⁶

Table 1 shows the list created by the laboratory scientists who participated in the workshop compared with the other two approaches (most frequently ordered tests and using the EML standard). It should be noted that the workshop participants were not told the list of tests in the WHO EDL, the EDL based on the EML, details of the WHO vertical programs, or the most frequently ordered tests in five hospitals from three different continents. Of interest, there are strong similarities with these lists: CBC is a must, followed closely by a CMP that includes electrolytes and liver function tests. What is striking are some of the dissimilarities: bacterial cultures were at the top of the laboratory scientists’ list but were not at the top of the frequently ordered tests in three different continents, highlighting the drawback to relying only on high-volume tests ordered by physicians. We challenged the laboratory scientists to think about immunohistochemistry and molecular tests, and they came up with an important array of tests to be performed on tissues. Also to note, for most of the chemistry tests and three of the hematology tests, all three approaches reached the same conclusion, while for two of the hematology tests, most of the microbiology tests, and half of the immunohistochemistry/molecular tests, the laboratory scientists and the list based on the EML standard reached the same conclusion. In some way or another, the manner in which overlapping consensus occurred using the different approaches suggests that representation from all areas, including laboratory scientists, ordering physicians, and WHO experts, is necessary to create a comprehensive list.

Each of the three approaches to produce an EDL has advantages and disadvantages. In many ways, each is complementary and accomplishes having basic tests included in a list. As the WHO has gone forward with the EDL, it is for laboratory practitioners and societies that represent them to support the effort so that countries around the world adopt and adapt the list, always remembering that the WHO EDL will be instrumental for having greater availability of tests in low- and middle-income countries.

Acknowledgments

We thank all laboratory scientists who participated in the Baltimore 2018 American Society for Clinical Pathology workshop for their contribution to this editorial.

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