Q&A column

Graham R. Jones, PhD
Forensic Toxicologist, Office of the Chief Medical Examiner
Clinical Professor
Department of Laboratory Medicine and Pathology
University of Alberta
Edmonton, Canada
Member, CAP Toxicology Committee

Q. Why do proficiency testing specimen results for common immunoassay analytes sometimes vary greatly with different instrument manufacturers and their reagents? Does that mean the patient’s results for the same specimen could vary greatly based on the instrument used? If so, is this acceptable? Wouldn’t the variation in results confuse the clinician and patient?

A.It is true that results for proficiency testing specimens for common immunoassay analytes sometimes vary with reagents from different manufacturers or even from the same manufacturer for the same analyte if different methods are used. This variability may be attributed to analytical and biological diversity and a lack of analyte harmonization and standardization. The absence of standardization is reflected by the use of diverse units and varying reference intervals.

To explain this observation, I would like to focus on autoimmune disease serologic testing. Heterogeneity in analytes for detecting the same antibody, diversity in immunological methods, and the use of manual versus automated instruments contribute to the variability in some CAP Surveys. Another major contributing factor is the lack of international standards or reagents to calibrate different assays of the same analyte. Lastly, biologic variability in host immune responses may inherently limit commutability between assays based on the type of analytes used. For example, a patient of a certain genetic background may respond to parts of an antigen (i.e. epitopes) that are not present in the immunoassay being used to evaluate that patient, thereby giving a false-negative result. Furthermore, each patient with a specific autoimmune disease may produce polyclonal antibodies that are unique in structure, selectivity, affinity, and avidity to the target antigen, making it difficult to establish a common standard.

It is very likely that a patient may get different results if the same specimen is tested using different immunoassays or instruments from different manufacturers. Lack of consensus in proficiency testing is likely an indirect measure of how variability in test performance characteristics may negatively impact patient results and patient evaluation and management. Comparable test performance implies patients will get the same result irrespective of the assay or method used or where the testing is conducted. It assures that health care providers can reliably evaluate and manage their patients. The clinical significance of discrepant results depends on how results are reported, interpreted, and communicated to the health care provider and used in the diagnosis and management of the patient.

It is very likely that discrepant results between immunoassays from different laboratories would confuse clinicians and patients. Understanding these limitations may help minimize confusion and potential harm to patients. Such scenarios are a major reason why there are several initiatives to harmonize or standardize laboratory tests at a global level. There are also a number of laboratory guidance documents and recommendations on how to validate, interpret, and communicate test results so that health care providers are familiar with these challenges and can act appropriately to avoid patient harm.

Jacobs JFM, Bossuyt X. Standardization and harmonization of autoimmune diagnostics. Clin Chem Lab Med. 2018;56(10):1563–1567.

Anne E. Tebo, PhD, D(ABMLI)
Co-director
Antibody Immunology Laboratory
Senior Associate Consultant
Division of Clinical Biochemistry and Immunology
Department of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine
Rochester, Minn.