A comprehensive review of competitive lateral flow assays over the past decade

Competitive lateral flow assays (LFAs) provide a versatile and cost-effective platform for detecting a wide range of molecular targets across fields such as healthcare, food safety, and environmental monitoring, particularly for small analytes or single epitopes that lack suitable bioreceptor pairs. However, the interpretation of competitive LFAs can be challenging due to their counterintuitive output, where the absence of a test line signifies the presence of the target. In this review, we present a comprehensive overview of the fundamental strategies underlying competitive LFAs, explore the mathematical models that quantify assay performance, and outline the critical parameters involved in their design and optimization. We further highlight notable applications and discuss methods to enhance the user experience through improved result interpretation and user-centric design. By consolidating current knowledge and best practices, this work will serve as a valuable reference for researchers and developers seeking to refine the usability, reliability, and effectiveness of competitive LFAs.

Comparison of analysis of serum free light chains in a cartridge-based protein analyzer Mispa i3 with Roche Cobas 8000

Serum-free light-chain assays are important in the diagnosis and in monitoring therapeutic responses of plasma cell disorders and are complementary to serum protein electrophoresis. The serum-free light-chain assay detects the light-chain portion of immunoglobulin in its free form with high sensitivity. In combination with serum protein electrophoresis and serum immunofixation electrophoresis, the free light-chain assay serves an important role in predicting disease progression in monoclonal gammopathy. Here, we compare the performance of a cartridge-based system Mispa i3 using Diazyme reagent in comparison to Roche Cobas using Freelite reagent. Both of these reagents use polyclonal antibodies for the detection of serum-free light chains. Mispa i3 is a cartridge-based protein analyzer and has a unique channel shifting technology with both turbidimetric and nephelometric principles for immuno assays. Samples of 196 patients were included in this study, and very good agreement was observed between these two assays. Our data show that even though discrepancies were observed for high concentration samples, they are clinically correlated by the free light-chain ratios. We observed a very good concordance of 89% between these two assays for free light-chain ratios.

A Comparative Analysis of Freelite and N Latex FLC Assay for the sFLC Measurements in Suspected Patients of Monoclonal Gammopathy

With the introduction of newer platforms for sFLC estimation, more comparative attempts are required to establish an assay-specific reference range, that can be used in the day-to-day clinical management of the patients, as the revised criteria for the diagnosis of myeloma recommend the use of involved Free light chain (FLC)/uninvolved FLC ratio as myeloma defining event, solely relying on Freelite assay. This was an observational study that included 101 patients, 55 (54.5%) with M-protein (myeloma), and 46 (45.5%) without M-protein. The estimation of the sFLC assay was carried out at two separate platforms, the Freelite Assay (The binding Site, Birmingham, UK) on a Siemens BNII Nephelometer, and the N Latex FLC reagent on Atellica NEPH 630 (Siemens Healthineers, Eschborn, Germany). The comparative correlational analysis of the two assays for estimation of κ-, λ FLC, and κ/λ ratio showed a strong to a very strong association (P-value < 0.005) among total patients, however, this was reduced to weak to moderate association among patients with M-protein (P-value < 0.005). The contingency analyses to evaluate the agreement between the assays also showed a similar trend. A better concordance for the κ/λ ratio between the two assays was achieved while expanding this ratio. Our study concluded that two assays showed a better agreement among the patients without M-protein, but these two cannot be used interchangeably for the clinical management of myeloma patients.

Lateral Flow Immunoassays for Detecting Viral Infectious Antigens and Antibodies

Abundant immunological assays currently exist for detecting pathogens and identifying infected individuals, making detection of diseases at early stages integral to preventing their spread, together with the consequent emergence of global health crises. Lateral flow immunoassay (LFIA) is a test characterized by simplicity, low cost, and quick results. Furthermore, LFIA testing does not need well-trained individuals or laboratory settings. Therefore, it has been serving as an attractive tool that has been extensively used during the ongoing COVID-19 pandemic. Here, the LFIA strip's available formats, reporter systems, components, and preparation are discussed. Moreover, this review provides an overview of the current LFIAs in detecting infectious viral antigens and humoral responses to viral infections.

Development of a Monoclonal Antibody and a Serodiagnostic Lateral-Flow Device Specific to Rhizopus arrhizus (Syn. R. oryzae), the Principal Global Agent of Mucormycosis in Humans

Mucormycosis is a highly aggressive angio-invasive disease of humans caused by fungi in the zygomycete order, Mucorales. Though a number of different species can cause mucormycosis, the principal agent of the disease worldwide is Rhizopus arrhizus, which accounts for the majority of rhino-orbital-cerebral, pulmonary, and disseminated infections in immunocompromised individuals. It is also the main cause of life-threatening infections in patients with poorly controlled diabetes mellitus, and in corticosteroid-treated patients with SARS-CoV-2 infection, where it causes the newly described disease, COVID-19-associated mucormycosis (CAM). Diagnosis currently relies on non-specific CT, a lengthy and insensitive culture from invasive biopsy, and a time-consuming histopathology of tissue samples. At present, there are no rapid antigen tests for the disease that detect biomarkers of infection, and which allow point-of-care diagnosis. Here, we report the development of an IgG1 monoclonal antibody (mAb), KC9, which is specific to Rhizopus arrhizus var. arrhizus (syn. Rhizopus oryzae) and Rhizopus arrhizus var. delemar (Rhizopus delemar), and which binds to a 15 kDa extracellular polysaccharide (EPS) antigen secreted during hyphal growth of the pathogen. Using the mAb, we have developed a competitive lateral-flow device (LFD) that allows rapid (30 min) and sensitive (~50 ng/mL running buffer) detection of the EPS biomarker, and which is compatible with human serum (limit of detection of ~500 ng/mL) and bronchoalveolar lavage fluid (limit of detection of ~100 ng/mL). The LFD, therefore, provides a potential novel opportunity for the non-invasive detection of mucormycosis caused by Rhizopus arrhizus.

Method comparison of three serum free light chain assays on the Roche Cobas 6000 c501 chemistry analyzer

OBJECTIVES

Free light chains (FLC) are important in the diagnosis, prognosis and monitoring of therapy response of patients with monoclonal gammopathies. In this study, we performed a method comparison of three FLC assays on the Cobas 6000 c501 chemistry analyzer of Roche Diagnostics.

METHODS

Samples of 119 patients with various monoclonal gammopathies and 26 control patients were measured with the Freelite (The Binding Site), Diazyme (Diazyme Laboratories) and KLoneus (Trimero Diagnostics) FLC assays. A method comparison was performed and reference intervals of the three assays were validated.

RESULTS

The analysis of the Bland-Altman agreement showed bias between the three FLC assays, ranging from -62.7 to 5.1% for κFLC and between -29.2 to 80.5% for λFLC. The Freelite and Diazyme assays have the highest agreement. The concordance of the FLC-ratio ranges from 41 to 75%, with the highest concordance between the Freelite and KLoneus assays. The FLC-ratio in 25 sera from healthy controls were within the reference ranges of the Freelite and KLoneus assays. The FLC-ratio was elevated in all 25 samples tested with the Diazyme assay.

CONCLUSIONS

The agreement for the free light chains is highest between the Freelite and the Diazyme assay and fair for the KLoneus assay. However, concordance of the FLC-ratio is highest when the Freelite and KLoneus assays were compared. Our data suggest that concordance for the Diazyme assay could be improved by recalibration. Because of absolute differences between the three methods in individual patients, none of the three FLC assays can be used interchangeably.

Monoclonal free light chain detection and quantification: Performances and limits of available laboratory assays

The detection and quantification of immunoglobulin free light chains in serum and urine is recommended for the diagnosis and monitoring of monoclonal gammopathies according to the guidelines of the International Myeloma Working Group (IMWG). Several tests are currently available in the clinical laboratory to detect and quantify free light chains but although quality, efficiency, and effectiveness have been improved, the results are still variable and poorly harmonized and standardized. The present review article wants to analyze these aspects, with a keen eye on techniques, such as mass spectrometry, that could replace in the practical clinical laboratory the current methods including Bence-Jones protein assay and free light chain immunoassays.

Serum free light chains in solid organ transplant recipients

Immunoglobulin is built by a pair of identical heavy and a pair of identical light chains. Light chains are produced in excess compared to heavy chains. Free light chains (FLCs) are those which are not combined with heavy chains. Currently, numerous assays are available for the measurement of serum FLCs (sFLCs). These assays cannot be used interchangeably, and renal function should be taken into account in interpreting test results. Levels of kappa and lambda sFLCs are usually used to diagnose and monitor plasma cell dyscrasias. However, the clinical relevance of sFLCs is being investigated in patients with a variety of diseases, including patients after transplantation. There are contradictory results regarding the usefulness of sFLCs in the prediction of post-transplant lymphoproliferative disorder (PTLD). However, it seems that sFLCs may be helpful in the prediction of early-onset PTLD. Some studies have shown that low levels of sFLCs are associated with a higher risk of infection in patients after transplantation. This review summarizes and highlights recent advances in the utility of sFLCs in the prediction of PTLD and infection, and inflammation assessment in patients after solid organ transplantation. Moreover, the influence of immunosuppressive treatment on sFLCs levels is described briefly.

Simplified formats of modern biosensors: 60 years of using immunochromatographic test systems in laboratory diagnostics

Immunochromatographic test systems known to foreign laboratory diagnostic experts as lateral flow immunoassay (LFIA) are simplified tape formats of modern biosensors. For 60 years, they have been widely used for the rapid detection of target molecules (ligands) in biosubstrates and the diagnosis of many diseases and conditions. The growing popularity of these test systems for providing medical care or diagnostics in developing countries, medical facilities, in emergency situations, as well as for individual home use by patients while monitoring their health are the main factors contributing to the continuous development and improvement of these methods, the emergence of a new generation of formats. The attractiveness and popularity of these fast, easy-to-use, inexpensive and portable diagnostic tools is associated primarily with their high analytical sensitivity and specificity, as well as the ease of interpretation of the results. These qualities have passed the test of time, and today LFIA test systems are fully consistent with the modern world concept of «point-of-care testing», finding wide application not only in medicine, but also in ecology, veterinary medicine, and agriculture. This review will highlight the modern principles of designing the most widely used formats of immunochromatographic test systems for clinical laboratory diagnostics, summarize the main advantages and disadvantages of the method, as well as current achievements and prospects of LFIA technology. Modern innovations aimed at improving the analytical characteristics of LFIA technology are interesting, promising and can bring additional benefits to immunochromatographic platforms that have gained popularity and attractiveness for six decades.

Six decades of lateral flow immunoassay: from determining metabolic markers to diagnosing COVID-19

Technologies based on lateral flow immunoassay (LFIA), known in some countries of the world as immunochromatographic tests, have been successfully used for the last six decades in diagnostics of many diseases and conditions as they allow rapid detection of molecular ligands in biosubstrates. The popularity of these diagnostic platforms is constantly increasing in healthcare facilities, particularly those facing limited budgets and time, as well as in household use for individual health monitoring. The advantages of these low-cost devices over modern laboratory-based analyzers come from their availability, opportunity of rapid detection, and ease of use. The attractiveness of these portable diagnostic tools is associated primarily with their high analytical sensitivity and specificity, as well as with the easy visual readout of results. These qualities explain the growing popularity of LFIA in developing countries, when applied at small hospitals, in emergency situations where screening and monitoring health condition is crucially important, and as well as for self-testing of patients. These tools have passed the test of time, and now LFIA test systems are fully consistent with the world's modern concept of ‘point-of-care testing’, finding a wide range of applications not only in human medicine, but also in ecology, veterinary medicine, and agriculture. The extensive opportunities provided by LFIA contribute to the continuous development and improvement of this technology and to the creation of new-generation formats. This review will highlight the modern principles of design of the most widely used formats of test-systems for clinical laboratory diagnostics, summarize the main advantages and disadvantages of the method, as well as the current achievements and prospects of the LFIA technology. The latest innovations are aimed at improving the analytical performance of LFIA platforms for the diagnosis of bacterial and viral infections, including COVID-19.

Evaluation of two serum free light chain quantitation methods, Freelite and Seralite, in the clinical laboratory with a view to switching immunoassay

BACKGROUND

Serum free light chain (sFLC) quantitation is central for plasma cell dyscrasias. Several assays are available and switching sFLC methods may be advantageous in certain laboratories. This study performed Freelite and Seralite simultaneously for samples received by the clinical laboratory over a 10 month period and compared quantitation and its impact on interpretation of patient results.

METHODS

Patients (N = 189) included multiple myeloma (MM) and related plasma cell cancers, monoclonal gammopathy of unknown significance (MGUS), AL amyloidosis and renal impairment. sFLC quantitation and clinical agreement was assessed between methods.

RESULTS

Clinical agreement was substantial at diagnosis (κ = 0.647, p < .01) and moderate for monitoring (κ = 0.591, p < .01). Good concordance was seen for MM and related plasma disorders and MGUS, with poorer agreement seen for AL amyloidosis. Case studies illustrated agreement in pattern of myeloma disease activity. Bland-Atman plots showed small mean bias but increasing variation between methods with increasing FLC concentrations. Passing-Bablok analysis confirmed systematic differences in quantitation between methods.

CONCLUSIONS

Despite differences in quantitation, overall, agreement was seen between the different sFLC platforms in relation to the clinical interpretation. As a rapid test without the need for large and expensive analysers, Seralite may be highly applicable in certain laboratories to enable in-house testing.

Method comparison of four clinically available assays for serum free light chain analysis

Background

Serum free light chain (sFLC) measurements are increasingly important in the context of screening for monoclonal gammopathies, prognostic stratification and monitoring of therapy responses. In this study we have performed a method comparison of four sFLC assays that are currently available for routine clinical use.

Methods

In a retrospective study, sFLC analyses were performed on a cohort that included 139 patients with various monoclonal gammopathies and 54 control sera without an M-protein. Method comparisons of the following four FLC assays were performed: Freelite (Binding Site), N-Latex FLC (Siemens), Seralite (Abingdon Health) and Sebia FLC (Sebia).

Results

Bland-Altman agreement analysis showed biases varying between −0.1 and 16.2 mg/L for κFLC, −6.0 and 6.8 mg/L for λFLC and −0.04 and 0.38 for the ratio of the involved to uninvolved FLC. Strong agreements were observed for FLC-concentrations below 100 mg/L. The clinical concordance of the κ/λFLC-ratio of the four methods varied between 86% and 92%. Significant quantitative differences were observed between the different methods, mainly in sera with high FLC concentrations. Most assays consistently overestimated FLC concentrations compared to SPE.

Conclusions

Good overall clinical concordances were observed between the four sFLC assays that were compared in this study. Although good agreements were observed between the FLC assays, significant absolute differences in FLC concentrations in individual patients can be seen, particularly at higher FLC concentrations. Because of inequivalent absolute sFLC values between the methods in individual patients, none of the four sFLC assays can be used interchangeably.

Inter-assay variability in automated serum free light chain assays and their use in the clinical laboratory

Serum κ and λ free light chain levels are markers of plasma cell proliferation, and their measurements have been included in recent guidelines by the International Myeloma Working Group for the management of patients with plasma cellular dyscrasias. Five in vitro diagnostic methods for the immunochemical quantification of serum free light chains (FLC) are available, three based on polyclonal antibodies (Freelite^®, The Binding Site; FLC ELISA κ and λ, Sebia; human κ and λ FLC, Diazyme Laboratories) and two on monoclonal antibodies (N Latex FLC, Siemens Healthineers; Seralite^®, Sebia). Several studies have shown that these methods cannot be used interchangeably for the follow-up of patients because measured κ and λ FLC concentrations may differ significantly, especially at high levels. Because no international reference material for the measurement of FLC is available, it is not possible to establish which method is the most accurate. For this reason, knowledge about the analytical and diagnostic performances of the assays used is important. The aim of this review is to describe the main analytical features of the κ and λ FLC assays and how they may influence the clinical use of these parameters.

Evaluation of a new free light chain ELISA assay: bringing coherence with electrophoretic methods

Background:

Serum free light chain (sFLC) measurements are increasingly important in the context of screening for monoclonal gammopathies, prognostic stratification, and monitoring of therapy responses. At the same time, analytical limitations have been reported with the currently available nephelometric and turbidimetric sFLC assays. We have evaluated a new quantitative sFLC ELISA for its suitability in routine clinical use.

Methods:

Reference ranges of the Sebia FLC assay were calculated from 208 controls. Assay interference, reproducibility, lot-to-lot variability, and linearity were assessed. Method comparison to the Freelite assay (Binding Site) was conducted by retrospective analysis of 501 patient sera.

Results:

Reference ranges of the Sebia κ/λFLC-ratio were 0.37–1.44. We observed good sensitivity (1.5 mg/L) and linearity in both polyclonal and monoclonal sFLC samples and never experienced antigen excess. Sebia FLC reproducibility varied between 6.7% and 8.1% with good lot-to-lot consistency. Method comparison with Freelite showed the following correlations: κFLC R=0.94, λFLC R=0.92 and κ/λFLC-ratio R=0.96. The clinical concordance of the κ/λFLC-ratio of both methods was 94%. Significant quantitative differences were observed between both methods, mainly in sera with high FLC concentrations. The Sebia monoclonal FLC concentrations were coherent with those obtained by serum protein electrophoresis (SPE). Freelite monoclonal FLC concentrations were consistently higher, with a mean 12-fold overestimation compared to SPE.

Conclusions:

The Sebia FLC assay provides a novel platform for sensitive and accurate sFLC measurements. The Sebia FLC showed good clinical concordance with Freelite. Further studies are warranted to confirm the clinical value of this assay.

Multiple myeloma can be accurately diagnosed in acute kidney injury patients using a rapid serum free light chain test

Background

Acute kidney injury (AKI) is common in patients with multiple myeloma (MM). Whether serum free light chain (sFLC) measurements can distinguish between myeloma and other causes of AKI requires confirmation to guide early treatment. A rapid and portable sFLC test (Seralite®) is newly available and could reduce delays in obtaining sFLC results and accelerate diagnosis in patients with unexplained AKI. This study evaluated the accuracy of Seralite® to identify MM as the cause of AKI.

Method

sFLCs were retrospectively analysed in patients with AKI stage 3 as per KDIGO criteria (i.e. serum creatinine ≥354 μmol/L or those on dialysis treatment) (n = 99); 45/99 patients had a confirmed MM diagnosis.

Results

The Seralite® κ:λ FLC ratio accurately diagnosed all MM patients in the presence of AKI: a range of 0.14–2.02 returned 100% sensitivity and specificity for identifying all non-myeloma related AKI patients. The sFLC difference (dFLC) also demonstrated high sensitivity (91%) and specificity (100%): an optimal cut-off of 399 mg/L distinguished between myeloma and non-myeloma AKI patients. We propose a pathway of patient screening and stratification in unexplained AKI for use of Seralite® in clinical practice, with a κ:λ ratio range of 0.14–2.02 and dFLC 400 mg/L as decision points.

Conclusions

Seralite® accurately differentiates between AKI due to MM and AKI due to other causes in patients considered at risk of myeloma. This rapid test can sensitively screen for MM in patients with AKI and help inform early treatment intervention.

Diagnosis and monitoring for light chain only and oligosecretory myeloma using serum free light chain tests

This study aims to guide the integration of serum free light chain (sFLC) tests into clinical practice, including a new rapid test (Seralite^® ). Blood and urine analysis from 5573 newly diagnosed myeloma patients identified 576 light chain only (LCO) and 60 non-secretory (NS) cases. Serum was tested by Freelite^® and Seralite^® at diagnosis, maximum response and relapse. 20% of LCO patients had urine FLC levels below that recommended for measuring response but >97% of these had adequate sFLC levels (oligosecretory). The recommended Freelite^® sFLC ≥100 mg/l for measuring response was confirmed and the equivalent Seralite^® FLC difference (dFLC) >20 mg/l identified. By both methods, ≥38% of NS patients had measurable disease (oligosecretory). Higher sFLC levels were observed on Freelite^® at all time points. However, good clinical concordance was observed at diagnosis and in response to therapy. Achieving at least a very good partial response according to either sFLC method was associated with better patient survival. Relapse was identified using a Freelite^® sFLC increase >200 mg/l and found 100% concordance with a corresponding Seralite^® dFLC increase >30 mg/l. Both Freelite^® and Seralite^® sensitively diagnose and monitor LCO/oligosecretory myeloma. Rapid testing by Seralite^® could fast-track FLC screening and monitoring. Response by sFLC assessment was prognostic for survival and demonstrates the clinical value of routine sFLC testing.

Serum free light chain quantitative assays: Dilemma of a biomarker

BACKGROUND

Serum free light chains detection assays are consistently meeting greater interest for the diagnosis and monitoring of monoclonal gammopathies and plasma cell dyscrasias. Nowadays, there are neither standardized methods nor reference material for the determination of free light chains; for this reason, it is important to compare two different assays used in clinical laboratory.

METHODS

We evaluated 300 serum samples from patients with B-cell disorders and compared the analytical performances of both assay. Each test was assayed on both testing platforms (Siemens Dade Behring BN II Nephelometer and SPAPLUS by The Binding Site). κ/λ ratios were determined and compared. Results were analyzed by Passing-Bablok and Bland-Altman plots to evaluate comparability of the two techniques and to determine bias.

RESULTS

The reproducibility of both assays is acceptable, reaching minimum and desirable analytical goals derived from biological variability. However, values are not interchangeable between systems. This study shows that the two systems do not allow results to be transferred from one method to the other even if they display good agreement.

CONCLUSION

Our study highlights the importance of elaborating an international standard for free light chains quantification in order to offer homogeneous results as well as guarantee harmonization of values among laboratories. Moreover, the assays should be validated in specific patient groups to determine that they are clinically fit for purpose.