Is bad testing better than no testing? Evaluating nonstandard testing requests in the laboratory

Prior to implementation of clinical testing, laboratories validate and verify assays rigorously to ensure high quality, reliable results. At a minimum, this includes performance characteristics such as accuracy, linearity, reference interval, and precision. It may also include analytic sensitivity and specificity.

Despite the diligence in characterizing test performance, most labs will, at some point, receive a request to test specimens that are suboptimal or not routinely used for a specific assay. In such cases, laboratorians face a critical decision: to reject the request and cancel the test, or to proceed with testing while acknowledging potential limitations in the reliability of the reported results. When these situations arise, laboratorians must carefully evaluate several factors to guide their decision-making process.At ADLM 2024, a scientific session explored these scenarios using real-world examples in a point-counterpoint debate. The debate was coupled withwith prerecorded videos from physicians and other treatment team members, explaining the rationale behind these unusual requests. This engaging discussion highlighted salient points and shared experiences that resonated with many laboratorians in the field.

Poor quality and atypical specimens

Generally, these types of requests will fall into two categories: Poor quality specimens, or atypical specimen types or sources (1, 2). Each presents unique challenges requiring careful evaluation.

Poor quality specimens may have interferences that significantly affect test performance, such as hemolysis or lipemia. When considering testing in these situations, some questions to consider may include:

• Can the sample be recollected without significant inconvenience or harm?
• Would a recollected sample still exhibit the same presence of the interference?
• How does the interference affect test accuracy (e.g., falsely elevated or decreased results)?
• Are the clinical circumstances unique, such that a result even in the presence of an interference provides valuable clinical decision-making insights?

Requests on nonstandard specimens such as alternative fluids require a different approach. Questions may include:

• Are there peer-reviewed studies demonstrating the clinical utility of the result in the requested specimen type?
• What are the clinical risks associated with a falsely elevated or falsely decreased result?
• Does the treatment team have a clear rationale for using this specimen type?
• Does the treatment team fully understand the analytical challenges involved?
• Does the request represent an isolated situation with unique circumstances, or is it likely to lead to ongoing requests for routine testing of the specimen type?

In addition to the above points, laboratorians also should consider the feasibility of including additional experimental controls to increase confidence in the reported result.

For example, if a nonstandard dilution is requested, laboratories can perform parallel dilutions using a sample with a previously reported numeric result to validate the dilution scheme. Testing on atypical specimen types could be accompanied by a matrix-mixing study or a spiking study to demonstrate reasonable recovery of the target analyte in the sample matrix.

Good practice involves clear documentation via means of specific comments indicating an atypical testing situation. Comments should specify the context of the test, such as specimen type, dilution request, or reporting in the presence of known interferences. However, one limitation of this approach is that comments may not be as readily visible as the result, requiring clinicians to take additional steps to view the disclaimers and supporting information.

Another critical aspect of nonstandard testing is how the results will be reported and filed in the electronic medical record. For example, if a bodily fluid result itself is charted under serum or plasma results, this could affect the trending of the results over time, potentially leading to clinical misinterpretation.

An intriguing discussion from the scientific session at ADLM 2024 centered on the justification of testing performed solely for the patient’s reassurance, without clear medical necessity — a practice often referred to as “psychosocial testing.” The concept is understandably controversial among laboratorians. As evidence-based medicine becomes increasingly central to the practice of laboratory medicine, the recognition of the patient’s holistic needs may be lost. Striking a balance between patient-centered care and scientific best practices will remain a dynamic and evolving challenge for laboratory medicine.

In all cases, the risk of reporting an incorrect result must be carefully weighed against the consequences of providing no result at all. Engaging in a conversation with the ordering provider is essential to ensure they understand the limitations and uncertainties of the test and gain insight into how the result will be interpreted and used in clinical decision-making.

Steven W. Cotten, PhD, DABCC, NRCC, FADLM is associate professor, director of automated chemistry and critical care testing, and codirector of clinical chemistry at the University of N.C. at Chapel Hill in Chapel Hill, North Carolina. +Email: [email protected]

Sarah A. Hackenmueller, PhD, DABCC, FADLM, is technical director, rapid response laboratories at Providence Health & Services in Portland, Ore. +Email: [email protected]

Yachana Kataria, PhD, DABCC, FADLM is medical director of clinical chemistry at Boston Medical Center in Boston, Mass.+Email: [email protected]

References

1. Sen Gupta P, Sharma M, Timms P. Laboratory samples deemed ‘unsuitable for analysis’ can be diagnostically useful. Clin Med (Lond) 2013; doi:10.7861/clinmedicine.13-3-309.
2. Cotten S.W., Block DR. A review of current practices and future trends in body fluid testing. J Appl Lab Med 2023; doi: 10.1093/jalm/jfad059