Clinical Laboratory Tests And Interpretation Book
Charlesetta Blare
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Background: The number and complexity of clinical laboratory tests is rapidly expanding, presenting primary care physicians with challenges in accurately, efficiently, and safely ordering and interpreting diagnostic tests. The objective of this study was to identify challenges primary care physicians face related to diagnostic laboratory testing and solutions they believe are helpful and available to them.
Methods: In this study, sponsored by the Centers for Disease Control and Prevention, a random sample of general internal medicine and family medicine physicians from the American Medical Association Masterfile were surveyed in 2011.
Results: 1768 physicians (5.6%) responded to the survey. Physicians reported ordering diagnostic laboratory tests for an average of 31.4% of patient encounters per week. They reported uncertainty about ordering tests in 14.7% and uncertainty in interpreting results in 8.3% of these diagnostic encounters. The most common problematic challenges in ordering tests were related to the cost to patients and insurance coverage restrictions. Other challenges included different names for the same test, tests not available except as part of a test panel, and different tests included in panels with the same names. The most common problematic challenges in interpreting and using test results were not receiving the results and confusing report formats. Respondents endorsed a variety of information technology and decision support solutions to improve test selection and results interpretation, but these solutions were not widely available at the time of the survey. Physicians infrequently sought assistance or consultation from laboratory professionals but valued these consultations when they occurred.
Conclusions: Primary care physicians routinely experience uncertainty and challenges in ordering and interpreting diagnostic laboratory tests. With more than 500 million primary care patient visits per year, the level of uncertainty reported in this study potentially affects 23 million patients per year and raises significant concerns about the safe and efficient use of laboratory testing resources. Improvement in information technology and clinical decision support systems and quick access to laboratory consultations may reduce physicians' uncertainty and mitigate these challenges.
Clinical laboratory test results are very important for diagnosis, monitoring, and screening. 70-80% of diagnostic decisions are based on laboratory results. Thus, it is imperative that clinicians understand laboratory tests and how to properly interpret results. Laboratory results must be interpreted using reference intervals that distinguish health from disease states. Clinicians must consider biological variation and the potential for false positive or negative results. The laboratory also has a responsibility to provide clinicians with information to assist in correct interpretation.Read less
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This report provides new CDC recommendations for tests that can support a diagnosis of syphilis, including serologic testing and methods for the identification of the causative agent Treponema pallidum. These comprehensive recommendations are the first published by CDC on laboratory testing for syphilis, which has traditionally been based on serologic algorithms to detect a humoral immune response to T. pallidum. These tests can be divided into nontreponemal and treponemal tests depending on whether they detect antibodies that are broadly reactive to lipoidal antigens shared by both host and T. pallidum or antibodies specific to T. pallidum, respectively. Both types of tests must be used in conjunction to help distinguish between an untreated infection or a past infection that has been successfully treated. Newer serologic tests allow for laboratory automation but must be used in an algorithm, which also can involve older manual serologic tests. Direct detection of T. pallidum continues to evolve from microscopic examination of material from lesions for visualization of T. pallidum to molecular detection of the organism. Limited point-of-care tests for syphilis are available in the United States; increased availability of point-of-care tests that are sensitive and specific could facilitate expansion of screening programs and reduce the time from test result to treatment. These recommendations are intended for use by clinical laboratory directors, laboratory staff, clinicians, and disease control personnel who must choose among the multiple available testing methods, establish standard operating procedures for collecting and processing specimens, interpret test results for laboratory reporting, and counsel and treat patients. Future revisions to these recommendations will be based on new research or technologic advancements for syphilis clinical laboratory science.
These recommendations were developed by CDC staff members on the basis of evidence published in peer-reviewed scientific journals. Data available in Food and Drug Administration (FDA)-cleared syphilis diagnostic test inserts were reviewed and assessed for consistency with published findings. In 2017, the Association of Public Health Laboratories (APHL) assisted with the literature review through an independent work group formed to evaluate the scientific literature for CDC to consider in the development of evidence-based recommendations for syphilis testing in the United States. APHL work group members were selected based on expertise in the field of syphilis and represented public health and commercial laboratory directors, public- and private-sector providers, and academic researchers. The work group leads were experienced in conducting systematic reviews of the literature. Potential conflicts of interest were disclosed to APHL and are listed at the end of the work group (Supplementary Appendix 1, ). APHL staff members reviewed potential conflicts and concluded that no work group members had a financial interest or ongoing relationships that might bias the literature review and subsequent discussions. The APHL work group did not rank the evidence and did not make any recommendations based on the scientific literature review. CDC staff members involved in ranking the evidence and drafting recommendations based on the scientific literature certified that they did not have a perceived or actual competing interest with respect to this activity.
Draft recommendations were peer reviewed as defined by the Office of Management and Budget for influential scientific information ( -review.htm). In February 2022, draft recommendations were peer reviewed by four experts in the field of syphilis who were not U.S Federal employees, were not funded by CDC for syphilis research, and were not involved in the development of these recommendations (Supplementary Appendix 3, ). Comments submitted during the external peer review were addressed, and the document was available for a 60-day public comment period beginning April 5, 2023. Draft recommendations were reviewed by subject matter experts and stakeholders, including APHL, the American Society for Microbiology, the Centers for Medicare & Medicaid Services (CMS), and FDA. After the public comment and stakeholder review, CDC considered all comments in the development of final testing recommendations for syphilis.
Syphilis serologic tests were developed at the beginning of the 20th century and used by medical personnel to diagnose syphilis. The first test, known as the Wassermann test, was a complement fixation test that used liver extracts, initially from fetuses and subsequently from the heart tissue of patients with syphilis (24). The assay was further standardized to improve reproducibility by laboratories after the publication of a method to isolate cardiolipin and lecithin (phosphorylcholine) from beef heart and combine them with cholesterol as the antigens for these tests (25). Subsequent tests involving immobilization of T. pallidum, agglutination, or flocculation were based on the same principle of detecting serum that reacted to T. pallidum (T. pallidum immobilization [TPI] test) or to antigens found in the membranes of T. pallidum (cardiolipin [diphosphatidylglycerol], phosphorylcholine, and cholesterol) used in the rapid plasma reagin (RPR) and Venereal Disease Research Laboratory (VDRL) tests. In 1954, the World Health Organization convened an expert committee on treponematoses and made recommendations regarding antigen preparation, standardization of tests, and terminology (26). The terminology was based on the understanding of the contemporaneous scientific findings and became the basis for which to describe the serologic testing concepts for syphilis that are still used today (27). Over time, the use of the terms nontreponemal tests, treponemal tests, and nonspecific antibodies should be revisited and updated to be consistent with the scientific evidence related to the immunobiology of T. pallidum.
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