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Immunochemistry Instruments and Reagents

Immunoassays – Interference, advancements, and alternatives

The laboratory must validate the technical standard and reproducibility of measurement through standard methodology and adequate quality management.

Immunoassays are powerful qualitative and quantitative analytical techniques. Since the first description of an immunoassay method in 1959, advances have been made in assay designs and analytical characteristics, opening the door for their widespread implementation in clinical laboratories. Clinical endocrinology is closely linked to laboratory medicine because hormone quantification is important for the diagnosis, treatment, and prognosis of endocrine disorders. Several interferences in immunoassays have been identified through the years; although some are no longer encountered in daily practice, cross-reaction, heterophile antibodies, biotin, and anti-analyte antibodies still cause problems. Newer interferences are also emerging with the development of new therapies. The interfering substance may be exogenous (e.g., a drug or substance absorbed by the patient) or endogenous (e.g., antibodies produced by the patient), and the bias caused by the interference can be positive or negative. The consequences of the interference can be deleterious when clinicians consider erroneous results to establish a diagnosis, leading to unnecessary explorations or inappropriate treatments. Clinical laboratories and manufacturers continue to investigate methods for the detection, elimination, and prevention of interferences. However, no system is completely devoid of such incidents.

Improvements in assay design, Ab structure and specificity, and signal generation and detection, with an increasing number of assays developed to detect more molecules, have made immunoassays one of the most used techniques in clinical laboratories. However, there has also been a trend to simplify methods to facilitate automation, and new innovative therapies result in new interferences.

Some of the major specificity problems in competitive assays are related to the measurement of steroids and structurally related compounds. Therefore, many laboratories have started using LC-MS/MS for the quantification of these analytes, although these methods are more expensive and technically demanding than immunoassays. LC-MS/MS avoids main specificity problems and also provides multi-parameter quantification in the same analytical session, allowing for steroid profiles to be generated with a dramatically reduced sample volume, which is valuable for newborns and infants.

Unfortunately, these powerful and reliable measurements are not yet adapted to high-throughput sandwich assays. As protein and macromolecule assays with LC-MS/MS become more amenable, the use of immunoassay-based measurements may decline to improve specificity and robustness with respect to immunological interference, notably for some critical assays, such as Tg as a major biomarker for the follow-up and management of differentiated thyroid cancer. While waiting for these improvements, immunoassays, despite their drawbacks, will still be in general use, at least for a few years, and the problem of immunoassay interference will persist.

Laboratory knowledge plays a central role in highlighting possible interference. When a clinician deals with unexpected or incoherent results regarding patient conditions, a strong interface with laboratory specialists facilitates the rapid identification of incoherent results. Informing the clinical staff of the ever-present possibility of unexpected sporadic interference, notably from an endogenous Ab, is needed.

When facing unknown interference, which might require more deep and specialized investigations, feedback from laboratory to manufacturers enables the manufacturers to actively search for a solution to the emerging problem and to keep improving the immunoassay robustness with respect to the risk of interference. Granting laboratory specialists access to the clinical and therapeutic records of patients is important when they suspect and try to detect interference.

Specifically, the notion of biotin or a specific therapy has become a key question. In addition, the notion of previously administrated immunotherapies must always draw the attention of laboratory specialists to the possibility of Ab-induced interference in immunoassays. Ideally, an interfering therapy should automatically be flagged; thus, minimizing interference risk can also be achieved by connections between health information systems and laboratory information systems.

“Rapid changes in diagnostic sector, coupled with parallel advances in digital transformation technology in clinical chemistry and immune assay platforms, have stimulated the evolution of approaches for artificial intelligence (AI) and robotic elements in routine laboratory process flow. Laboratory processes need to be streamlined to ensure provision of reliable and timely test results, appropriate alliance with brain-to-brain loop, thus enhancing quality of care and patient safety.

The implementation of AI, cloud computing, machine learning, and adoption of paperless workflows are instrumental in the transformation of the laboratory, more specifically, influencing clinical validation, procedure efficiency, data handling, data analysis, and much more. AI helps in computing risk-stratification score of laboratory data and clinical data, using expert system and evidence-based guidelines. Increasing cost-containment pressures make the application of this technology highly approachable.

Thus, implementation of digital transformation in the clinical chemistry and immunology laboratory improves revenues, suggests patient specific next steps, tests utilization, improves quality, standardizes treatment protocols as per local and international guidelines, improves patient satisfaction, provides patient-specific interpretation and next steps, improves standardized care by flagging patients, applies risk algorithms, and provides better interpretation. Dr Barnali Das, Consultant, Laboratory Medicine, Kokilaben Dhirubhai Ambani Hospital.

The monoplex/simplex immunoanalytical techniques are widely used as diagnostic or analytical tools in biomedical research for the detection and quantification of specific antigens or antibodies in a given sample through the method of enzyme-linked immunosorbent assay (ELISA). However, some diagnostic laboratories and organizations employ alternative screening analytical platforms, such as the microarray and multiplex immunoassays.

The multiplex assay is the simultaneous on-site detection of different analytes from a single specimen and has recently gained importance in clinical diagnostics or directly at POC. These techniques are based on protein or antibody microarrays or chips, coated beads, glass fibers, or microcapillary discs, using immobilized RNA, DNA, cDNA, and aptamers. The multiplex reactions are sometimes advantageous over conventional immunoassays by performing many reactions and the ability to extract more information from the same sample in a fast and efficient manner.

However, multiplex assays are not available in most diagnostic laboratories and require expensive equipment and trained personal. The multiplex assays require advanced methodology or/and technology, such as fluorescence or chemiluminescence (PCR, ELISA), assays (microarrays, gel electrophoresis), and signals (capillary electrophoresis). The lateral flow immunoassay (LFIA) is one of the most successful analytical platforms for the on-site detection of target substances. The features of LFIA have made them a very important and significant tool in clinical diagnostic where they can improve patient care by enabling prompt diagnosis and treatment. The goal of reducing the time and cost of drug development are the incentives and driving forces to find alternatives to animal testing that may bring about an improvement in identifying human safety and toxicity for therapeutics.

In addition, accurate identification of agents that are human-safe will increase potential effective therapeutics in human diseases. The alternatives to animal research, such as cell and tissue platforms, computational in silico modelling, 3D tissue platforms, and organ-on-chip research have shown great promise in diagnostics and pharmacology and may have a significant impact on advancements and technological developments.

Immunoassays are inherently fragile but will remain in practice for many hormone measurements for years to come. Changes in medical practice and development of new therapies and sociological trends (such as biotin-loaded dietary supplements) might affect immunoassay-based diagnoses. New interferents will be identified; therefore, laboratory specialists should not ignore or underestimate immunoassay weaknesses and should establish a bi-directional, open, and permanent dialogue with clinicians to rapidly identify any suspected results before making further diagnostic or therapeutic decisions.

Research Corner
Existing methods for detecting and diagnosing Covid-19 are either expensive and complex or inaccurate. Now, scientists from the Gwangju Institute of Science and Technology have developed a novel biosensing platform to detect and quantify viral particles, using a simple optical microscope and antibody proteins. Their versatile approach, based on slowing down light, could pave the way to new diagnostic tools and next-generation detection platforms that are fast, accurate, and low-cost.

Despite all the bad news the Covid-19 pandemic brought upon the world, it has helped us gain a better perspective of our readiness to fend off highly contagious diseases. Rapid diagnostic test kits and PCR testing quickly became essential tools when the pandemic hit, helping with timely diagnoses. However, these tools have inherent limitations. PCR tests are complex and require expensive equipment while rapid diagnostic test kits have lower accuracy.

Against this backdrop, a research group led by Professor Young Min Song of the Gwangju Institute of Science and Technology in Korea has recently developed a new technique to easily visualize viruses using an optical microscope. A recent study explains in detail the operating principle of their detection platform, called the Gires-Tournois immunoassay platform (GTIP). This paper was made available online on March 22, 2022, and was published in the journal Advanced Materials on March 26, 2022.

The key element of GTIP is the Gires-Tournois resonance structure, a film made from three stacked layers of specific materials that produce a peculiar optical phenomenon called slow light. Because of how incident light rebounds inside the resonant layers before being reflected, the color of the platform seen through an optical microscope appears very uniform. However, nanometer-sized virus particles affect the resonance frequency of GTIP in their immediate vicinity by slowing down the light that gets reflected around them. The slow light manifests as a vivid color change in the reflected light so that when viewed through the microscope, the virus particle clusters look like islands of a different color compared to the background.

To ensure that their system only detects coronavirus particles, the researchers coated the top layer of GTIP with antibody proteins specific to SARS-CoV-2. Interestingly, not only did the system enable the detection of viral particles but, by using colorimetric analysis techniques, the researchers could even effectively quantify the number of virus particles present in different areas of a sample, depending on the color of the light reflected locally.

The overall simplicity of the design is one of the main selling points of GTIP. As Prof. Song explains, “Compared to existing Covid-19 diagnostic methods, our approach enables rapid detection and quantification of SARS-CoV-2, without needing extra sample treatments, such as amplification and labeling.” Given that optical microscopes are available in most laboratories, the method developed by the group could become a valuable and ubiquitous diagnostic and virus research tool.

Furthermore, GTIP is not limited to detecting viruses or strictly dependent on antibodies; any other binding agent works as well, helping visualize all kinds of particles that interact with light. “Our strategy can even be applied for a dynamic monitoring of target particles sprayed in the air or dispersed on surfaces. We believe that this approach could be the basis for next-generation biosensing platforms, enabling simple yet accurate detection,” concludes Prof. Song.

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