The investigation of interferences in immunoassay

Highlights

• Procedures for investigation of unusual or unexpected immunoassay results

• Practical approach based on personal experiences for routine non-specialised laboratories

• Summary of common interferences

Abstract

Immunoassay procedures have a wide application in clinical medicine and as such are used throughout clinical biochemistry laboratories both for urgent and routine testing. Clinicians and laboratory personnel are often presented with immunoassay results which are inconsistent with clinical findings. Without a high index of suspicion interferences will often not be suspected. Artifactual results can be due to a range of interferences in immunoassays which can include cross reacting substances, heterophile antibodies, autoantibodies and the high dose hook effect. Further, pre-analytical aspects and certain disease states can influence the potential for interference in immunoassays. Practical solutions for investigation of artifactual results in the setting of the routine clinical laboratory are provided.

Introduction

Most clinicians accept laboratory results at face value and do not query the validity of that result. For this reason the laboratory has a particular responsibility to ensure the validity of the results they release.

Immunoassay is an important part of the diagnostic pathology laboratory, and because of the relatively low concentrations of analyte being measured and because of the complexities of the antigen-antibody interaction, this technique is relatively susceptible to interferences.

In some areas, possible interferences may be highly problematic and highly visible. A good example is with the use of troponin in assessing the person with possible acute coronary syndrome. The presence of troponin is a core part of the diagnosis of myocardial infarction and results are frequently required urgently. We have had patients present with a relatively constant concentration of troponin regardless of whether they are experiencing chest pain, suggesting that the apparent troponin result is artifactual. With such patients it is of considerable importance to sort out what is happening – is an interferent present or is the troponin result real?

However, with many assays there may never be reason to suspect the presence of an interferent as the results may be open to interpretations that can handle a variety of results. An example of this is serology looking at possible infections, where either a negative or a positive result can be rationalised on clinical grounds.

The purpose of this review is not so much to identify the mechanisms of immunoassay interferences – there have been many excellent reviews published on this topic [1], [2], [3], [4], [5], [6], [7], [8] – but rather to discuss ways of becoming aware of possible interferences and how to investigate them. We have deliberately concentrated on relatively simple procedures that will be available in non-specialist laboratories.