COMMENTARY

Laboratory Results That Should Be Ignored

Dirk M. Elston, MD

Disclosures

October 11, 2006

Effective Use of Interpretative Reports

Interpretative reports are crucial when a laboratory result should be ignored, but even accurate results may be misinterpreted, and interpretative reports have dramatic potential to reduce medical errors and unnecessary follow-up testing.[40,41,42] Accurate interpretation of test results depends on patient history, experience of the interpreter, and local disease prevalence. When the pretest likelihood of disease is small, there will be a larger number of false positives.[43] In the preanalytic phase, redirecting test ordering has the potential to reduce false-positive results stemming from testing patients in low-prevalence populations. In the postanalytic phase, computer graphs have been used to show post-test probability of disease as a function of pretest probability.[44]

Interpretative reports vary from graphic representation of normal ranges to elaborate mathematic models. Computer systems have facilitated interpretive reporting, especially for high-volume and high-complexity laboratory tests.[45,46,47,48] Automated laboratory analyzers can present laboratory results in graphic form relative to population-based data. Graphic reports with manually added interpretative text can be of additional value in conveying results effectively.[49] Critical differences (as well as those differences that are clinically insignificant) must be clearly communicated in graphic reports. The reporting interval or bin size that is used to report numerical results influences interpretations of the critical difference between results. As the reporting interval size increases, there is a roughly linear increase in the appearance of a critical difference.[50] Standard reporting intervals must be integrated with data in regard to what difference is clinically relevant.[51]

When reporting culture results, the growth of organisms that usually represent normal flora is complicated by the fact that the same organisms can sometimes act as opportunistic pathogens.[52,53] The line between normal flora, colonist, and pathogen may be poorly defined.[54,55] It has been traditionally left to the clinician to determine the clinical significance of the organism, but as our understanding of the role of virulence factors in opportunistic infection and immune-mediated diseases evolves, laboratories will have a more defined role in communicating the possible clinical significance of various organisms. Interpretive reports are also being used to communicate bacterial susceptibility test results effectively.[56]

The wording of interpretative reports is critical, and it may be helpful to have standard comments reviewed by panels of clinicians. In one study of the quality of interpretative comments in clinical chemistry, the study authors found that a significant proportion of well-intended comments were considered to be misleading by a panel of clinicians.[57] A study of computer-based interpretative reporting of endocrine studies found that interpretative reports were valued more highly by clinicians when the interpretative comments were specific to the test result, stated as considerations rather than recommendations, and accompanied by an expanded list of differential diagnoses and a listing of drugs that are known to affect the test result.[58]

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