Characteristics of isatuximab-derived interference in serum protein electrophoresis and immunofixation, and an absence of sustained in vivo interference due to belantamab mafodotin and denosumab

OBJECTIVES

Some therapeutic monoclonal antibodies, like daratumumab and elotuzumab, produce interfering monoclonal bands on serum protein electrophoresis (SPEP) and immunofixation electrophoresis (IFE). Whether other common therapeutic antibodies also produce interference has not been systematically evaluated.

DESIGN AND METHODS

SPEP/IFE from patients receiving isatuximab (48 patients), belantamab mafodotin (BM; 41), and denosumab (41) were retrospectively reviewed for therapeutic antibody interference. Cases exhibiting isatuximab interference were quantified and the maximum duration of isatuximab effect was evaluated. To characterize band position, neat human serum was spiked with BM or denosumab at supratherapeutic concentrations. Band migration patterns were compared on SPEP and IFE, with band position expressed relative to other constant protein fractions.

RESULTS

Isatuximab-induced IFE interference was common (81.3 % of evaluated patients) with a maximum observed duration of 8 weeks. 10.4 % of isatuximab patients had IgG kappa monoclonal gammopathies that co-migrated with the drug; this subset could benefit from HYDRASHIFT 2/4 isatuximab testing. 8.3 % of IFE cases were negative for an isatuximab band but showed large, endogenous M-spikes migrating elsewhere. All patients in this group expired within 1 year of this finding. We hypothesize that an inability to detect isatuximab in this setting corresponds to a large residual myeloma burden that reduces isatuximab serum concentration. This observation may serve as a negative prognostic factor. Spiking studies demonstrated that BM and denosumab produce interference in vitro, but sustained interference was not observed in >40 treated patients.

CONCLUSIONS

Therapeutic antibody interference in patients receiving isatuximab is common, and can persist for at least 8 weeks after administration. >10 % of patients receiving isatuximab may benefit from HYDRASHIFT testing post-therapy. In contrast, BM and denosumab fail to produce sustained interference in treated patients.

Assay interference as a cause of false positive troponin T elevation in emergency department patients

BACKGROUND

Troponin assays are used in the diagnosis of myocardial injury and may show elevated results for a variety of reasons. However it is increasingly recognised that cardiac troponin elevation may in some cases be due to assay interference. This is of significant importance as a misdiagnosis of myocardial injury may lead to unnecessary and potentially harmful investigation and treatment for patients. We sought to confirm the accuracy of cardiac high sensitivity troponin T (chsTnT) elevation in an unselected group of patients presenting to the emergency department, by using a second confirmatory cardiac high sensitivity troponin I (chsTnI) assay.

METHODS

We identified patients presenting to two local emergency departments over a five-day period who had chsTnT levels measured as part of routine clinical care. All samples with elevated chsTnT levels (above the 99% centile URL) were retested for chsTnI in order to confirm true myocardial injury.

RESULTS

A total of 74 samples from 54 patients were analysed for chsTnT and chsTnI. 7 samples (9.5%) had chsTnI levels < 5 ng/L suggesting assay interference as the cause of chsTnT elevation.

CONCLUSIONS

Assay interference leading to false positive troponin elevation may be more common than many physicians appreciate and can potentially lead to harmful investigation and treatment for patients. In cases where the diagnosis of myocardial injury is uncertain, a second alternative troponin assay should be performed to confirm true myocardial injury.

The necessity for improving lipid testing reagents: A real world study

BACKGROUND

We investigated the interference of vitamin C (VitC), glycerol fructose, lipoprotein X (LpX) and lipemia on the analysis of serum lipids.

METHODS

Serum were collected from 44 patients with VitC infusion, serum lipid concentrations before and after VitC auto-oxidation were compared. Serum of 31 patients with glycerol fructose infusion were collected, triglycerides (TG) measured by glycerol blanking and non-blanking reagents were compared. Forty-four serum samples suspected to contain LpX were collected, LDL-C measured by reagents from five manufacturers were compared. Lipemia samples were collected, LDL-C measured using five different reagents were compared. The interference rate was considered unacceptable if it was greater than 1/2 total allowable error (TEa).

RESULTS

In patients with VitC infusion, the interference rates of TG and total cholesterol (TC) were -59% (-123%, -28%) and -15% (-21%, -11%), respectively. In patients with glycerol fructose infusion, the interference rate of TG was 13% (4%, 113%). LpX interference led to increased LDL-C results for most reagents. Lipemia caused great interference with LDL-C analysis.

CONCLUSION

VitC, glycerol fructose, LpX and lipemia significantly interfered with lipid assays. The reagent formulation should be improved to get reliable results.

Falsely decreased vancomycin caused by rheumatoid factor: A case report

BACKGROUND

Vancomycin is associated with potential nephrotoxicity and trough concentrations need to be monitored in certain patients. Falsely decreased vancomycin measurement may result in overtreatment and need to be identified promptly by clinicians and pharmacists to avoid toxicities.

METHODS AND RESULTS

We report a case of rheumatoid factor-mediated falsely low vancomycin measurement with Abbott particle-enhanced turbidimetric inhibition immunoassay (PETINIA) method. Reanalyzing the sample using an alternative method, removing the interferences using heterophile blocking reagent as well as rheumatoid factor clean-up solution all helped to solve the false results. Results from alternative method and interference studies showed vancomycin concentrations reached toxic concentrations in the patient and administration of the drug was immediately terminated. The patient experienced a transient increase in serum creatinine.

CONCLUSIONS

Even though most modern immunoassays use blocking agents to neutralize interfering antibodies such as rheumatoid factor, it is important for health care professionals to understand that occasional interference still occurs due to the heterogeneous nature of rheumatoid factor.

Effects of EDTA on chemiluminescent immunoassay measurement of ACTH, cortisol, and thyroid hormones in dogs

When measuring blood hormones, pre-analytical sample handling can impact the quality of the results. Previous studies have shown improved stability of canine cortisol in ethylenediaminetetraacetic acid (EDTA) plasma compared to serum and interchangeability of serum and plasma when cortisol is measured by radioimmunoassay. Additionally, cortisol samples were also interchangeable when measured by chemiluminescent immunoassay if the EDTA concentration was consistent with that of optimally filled tubes, whereas excess EDTA interfered with the measurement of cortisol and serum and EDTA plasma were not interchangeable when measuring total thyroxine (TT4). The main limitation of these studies was that they were performed by spiking pooled serum samples with EDTA or in previously collected blood samples submitted to a clinical pathology laboratory. The purpose of the present study was to evaluate the effect of EDTA on the measurement of adrenocorticotropic hormone (ACTH), cortisol, TT4, free thyroxine (FT4), and thyroid stimulating hormone (TSH) in healthy dogs using the Siemens IMMULITE 1000. Whole blood from forty dogs was aliquoted into three Monoject sample tubes: no additive, completely filled EDTA tube, and 50% filled EDTA tube. Handling and storage conditions were identical, and all samples were analyzed on the same day. Bland-Altman plots and Passing-Bablok regression were used to assess agreement and risks for error, respectively. Proportional errors were found between serum and plasma samples for ACTH, cortisol, TT4, FT4, and TSH; systematic errors were also found for FT4. There was poor agreement and clinically significant differences between the measured concentrations of all hormones in serum and plasma, proving that these sample types are not interchangeable. Incompletely filled EDTA tubes were associated with significantly lower ACTH concentrations compared to completely filled EDTA tubes. When measured by chemiluminescent immunoassays that utilize alkaline phosphatase at the reporter enzyme, serum should be used for cortisol, TT4, FT4, and TSH, while plasma from completely filled EDTA tubes should be used for ACTH.

Promoting GAINs (Give Attention to Limitations in Assays) over PAINs Alerts: no PAINS, more GAINs

Many concepts and guidelines in medicinal chemistry have been introduced to aid in successful drug discovery and development. An example is the concept of Pan-Assay Interference Compounds (PAINS) and the elimination of such nuisance compounds from high-throughput screening (HTS) libraries. PAINs, along with other guidelines in medicinal chemistry, are like double-edged swords. If used appropriately, they may be beneficial for drug discovery and development. However, rigid and blind use of such concepts can hinder productivity. In this perspective, we introduce GAINS (give attention to limitations in assays) and highlight its relevance for successful drug discovery.

Optimization of hemolysis, icterus and lipemia interference thresholds for 35 clinical chemistry assays

Objectives

Interference of chemistry assays by hemolysis, icterus and lipemia (HIL) was investigated on the Abbott Alinity c system. We sought to empirically establish optimized HIL index thresholds for the purposes of reporting HIL interference in a hospital laboratory and advising clinicians on the interpretation of laboratory results in the presence of hemolysis, icterus or lipemia.

Methods

HIL index values measured by spectrophotometry were compared with concentrations of hemoglobin, bilirubin and Intralipid. HIL interference of 35 Abbott Alinity chemistry assays was subsequently investigated by pairwise comparison of test results in pooled serum or plasma with those in test preparations spiked with hemolysate, bilirubin or Intralipid. Data generated from the interference experiments were critically assessed according to assay-specific acceptance criteria adapted from multiple sources, and optimized thresholds for HIL indices were established.

Results

Correlations between HIL index values and their corresponding concentrations of hemoglobin, bilirubin and Intralipid were, in general, very good within the ranges of interferent concentrations tested. Hemolysis significantly affected 12 of 35 assays, whereas bilirubin and Intralipid interfered with four and three assays, respectively. Both the direction and magnitude of Intralipid interference with the direct bilirubin assay were dependent on the concentrations of the analyte.

Conclusions

HIL interference of the Abbott Alinity clinical chemistry assays investigated in this study was not uncommon. At present, there are no universally accepted criteria for defining significant assay interference for clinical practice. In establishing acceptance criteria for defining assay interference, each assay should be assessed according to both analytical criteria and clinical relevance.

Heterophilic antibody interference with TSH measurement on different immunoassay platforms

INTRODUCTION

Interference due to the presence of heterophilic antibodies may lead to falsely low or high analyte concentrations, but falsely elevated values are more common in most immunoassay platforms. We report a case of a 53-y old female patient underwent radical thyroidectomy for thyroid papillary carcinoma and the results of TSH in the Siemens Advia Centaur XP after surgery were not suppressed, ranging from 5.73 and 6.61 μIU/ml.

METHODS

The status of the thyroid was then assessed using 4 assay platforms from Siemens, Abbott, Roche and Beckman.

RESULTS

The results of TSH were 5.52, 0.54, 0.12, and <0.015 μIU/ml, respectively. After the samples were pretreated with the heterophilic antibody blocker, results given by Siemens, Abbott, and Roche showed significant decreases of 0.003, 0.001, and 0.005 μIU/ml, respectively. Therefore, it was confirmed that the presence of heterophilic antibodies in the patient samples interfered with the TSH measurements in multiple assay systems.

CONCLUSIONS

Clinicians must be aware of the possible assay interference, including the measurements of FT4, FT3 and TSH, results may be misleading in the presence of heterophilic antibodies, in particular when the results of thyroid function tests do not fit the patient clinical presentation.

Change in troponin concentrations in patients with macrotroponin: An in vitro mixing study

INTRODUCTION

Macrotroponin is a complex formed between endogenous cardiac troponin autoantibodies (cTnAABs) and circulating cardiac troponin (cTn). The potential effect of macrotroponin on current high sensitivity cTn assays has not been fully explored but has recently been identified as a major cause of discrepancy in cTn results between assays. In this study we investigated the effects of mixing troponin (cTn) standards to specimens with and without macrotroponin.

METHOD

Macrotroponin was identified in specimens by a recovery of cTnI < 40% following protein A immunoglobulin depletion. Troponin standards containing cTn-IC and cTn-TIC complexes were mixed with serum samples, with (n = 20) and without (n = 10) the presence of macrotroponin. Specimens were tested for cTn before and after mixing by three commercially available high sensitivity cTn assays. Gel filtration chromatography was carried out on five specimens with macrotroponin and each fraction was analzyed by multiple cTn assays.

FINDINGS

Following mixing with cTn-TIC standard, all specimens with macrotroponin had a markedly reduced absolute increase in cTnI, indicating negative analytical interference due to macrotroponin. Following mixing with the cTn-IC standard, specimens with macrotroponin demonstrated highly variable changes in cTnI, suggesting significant heterogeneity in macrotroponin complex reactivity between individuals. When the ratio of change, calculated by dividing the absolute change between two cTn assays, was compared between specimens with and without macrotroponin, significant differences were observed (p < 0.001). These findings were supported by variable migration of peak cTn activity on gel filtration chromatography.

CONCLUSION

Macrotroponin leads to assay dependent analytical interference affecting current high sensitivity troponin I assays. Furthermore, endogenously occurring cTnAABs are conformationally specific and the analytical effects vary between assays and individuals.

Data on interference indices in body fluid specimens submitted for clinical laboratory analysis

Clinical chemistry analysis of body fluids from non-blood or urine sources presents a technical challenge for clinical laboratories. Examples of body fluids include biliary secretions, cerebrospinal fluid, cyst contents, dialysate, gastric aspirates, peritoneal fluid, pleural fluid, stool, surgical drain fluid, synovial fluid, and wound exudates. The heterogeneous nature of these body fluids presents technical difficulties for analysis. For example, body fluid specimens may have presence of hemolysis, icterus, or lipemia (‘interference indices’) that can interfere with clinical chemistry analysis. In the related research article, we analyzed the distribution of these interference indices and body fluid samples submitted for analysis at an academic medical center central clinical laboratory and compared this to data from serum/plasma specimens. The data in this article provide the body fluid type, clinical chemistry testing ordered, interference indices, and whether the indices exceeded the manufacturer's recommendations in the package insert for serum/blood specimens. The analyzed data are provided in the supplementary tables included in this article. The dataset reported is related to the research article entitled “Review of interference indices in body fluids specimens admitted for clinical chemistry analyses” [1].

Data on hydroxychloroquine interference with urine laboratory testing

Hydroxychloroquine is a medication used to treat rheumatoid arthritis, systemic lupus erythematosus, and other autoimmune disorders. Previous studies have shown that hydroxychloroquine and the structurally related drug chloroquine have the potential to interfere with some common urine chemistry tests, especially at high concentrations. In the related research article, we observed suspected interference with urine drug of abuse testing in a patient who ingested approximately 12 g of hydroxychloroquine in an acute overdose, with urine hydroxychloroquine concentrations exceeding 500 mg/L. This case prompted a more detailed investigation of the effects of hydroxychloroquine spiked into pooled de-identified urine specimens from a hospital clinical laboratory. The data in this article provides the raw data for 24 urine assays that were investigated. The analyzed data is provided in the tables included in this article. The dataset reported is related to the research article entitled “Diagnostic Pitfalls and Laboratory Test Interference After Hydroxychloroquine Intoxication: A Case Report” [1].

Characterisation of utrophin modulator SMT C1100 as a non-competitive inhibitor of firefly luciferase

Firefly luciferase (FLuc) is a powerful tool for molecular and cellular biology, and popular in high-throughput screening and drug discovery. However, FLuc assays have been plagued with positive and negative artefacts due to stabilisation and inhibition by small molecules from a range of chemical classes. Here we disclose Phase II clinical compound SMT C1100 for the treatment of Duchenne muscular dystrophy as an FLuc inhibitor (K_D of 0.40 ± 0.15 µM). Enzyme kinetic studies using SMT C1100 and other non-competitive inhibitors including resveratrol and NFκBAI4 identified previously undescribed modes of inhibition with respect to FLuc's luciferyl adenylate intermediate. Employing a photoaffinity strategy to identify SMT C1100's binding site, a photolabelled SMT C1100 probe instead underwent FLuc-dependent photooxidation. Our findings support novel binding sites on FLuc for non-competitive inhibitors.

Phlebotomy tube interference with nuclear magnetic resonance (NMR) lipoprotein subclass analysis

BACKGROUND

Lipoprotein subclass analysis by nuclear magnetic resonance (NMR) can be used in risk assessment of atherosclerotic cardiovascular disease (ASCVD). There is little information in the literature regarding phlebotomy tube interferences with NMR testing.

METHODS

Pooled human serum was exposed to phlebotomy tubes manufactured by Becton Dickinson (BD), Greiner Bio-One, or Sarstedt. Serum was analyzed on the Axinon lipoFIT by NMR assay and by conventional lipid assays performed on a Roche Cobas 8000 system. The effect of incomplete fill volume was also assessed.

RESULTS

Analytical interference in NMR lipoprotein subclass results was observed across many different tube types. The 5 mL Greiner Bio-One Z Serum Sep Clot Activator tube correlated the best with non-gel containing serum tubes from BD and Greiner Bio-One. BD Serum Separator Tubes (SSTs) displayed strong interferences across several NMR analytes that were enhanced with decreased tube fill volumes. Interferences were also observed with different sizes of Greiner Bio-One Z Serum Sep Clot Activator tubes. Interference was generally not observed with conventional lipid testing, although minor interference was found for some tubes with lipoprotein(a) [Lp(a)].

CONCLUSIONS

NMR lipoprotein subclass analysis should be standardized by both tube type and tube size to prevent risk of analytical interference.

Silver nanoparticles: Significance of physicochemical properties and assay interference on the interpretation of in vitro cytotoxicity studies

Silver nanoparticles (AgNPs) have generated a great deal of interest in the research, consumer product, and medical product communities due to their antimicrobial and anti-biofouling properties. However, in addition to their antimicrobial action, concerns have been expressed about the potential adverse human health effects of AgNPs. In vitro cytotoxicity studies often are used to characterize the biological response to AgNPs and the results of these studies may be used to identify hazards associated with exposure to AgNPs. Various factors, such as nanomaterial size (diameter), surface area, surface charge, redox potential, surface functionalization, and composition play a role in the development of toxicity in in vitro test systems. In addition, the interference of AgNPs with in vitro cytotoxicity assays may result in false negative or false positive results in some in vitro biological tests. The goal of this review is to: 1) summarize the impact of physical-chemical parameters, including size, shape, surface chemistry and aggregate formation on the in vitro cytotoxic effects of AgNPs; and 2) explore the nature of AgNPs interference in in vitro cytotoxicity assays.

The effect of foetal bovine serum supplementation upon the lactate dehydrogenase cytotoxicity assay: Important considerations for in vitro toxicity analysis

The lactate dehydrogenase (LDH) assay is a commonly-used tool for assessing toxicity in vitro. However, anecdotal reports suggest that foetal bovine serum (FBS) may contain LDH at concentrations significant enough to interfere with the assay and thus reduce its sensitivity. A series of experiments were performed to determine whether addition of FBS to culture medium significantly elevated culture media LDH content, and whether replacement of FBS with heat inactivated foetal bovine serum (HI-FBS) reduced LDH content and interfered with cell response to cytotoxic challenge. The addition of FBS at 5, 10 and 15% final concentrations increased culture medium LDH content in a dose-dependent manner. The substitution of HI-FBS for FBS reduced culture medium LDH content and increased the dynamic range of the assay. Cell viability of the SH-SY5Y human neuroblastoma and N27 rat mesencephalic neurone cell lines were significantly reduced as measured using the MTT reduction assay, whilst HI-FBS only affected toxicity response in a cell- and toxin-specific manner, although these effects were small. Hence, for cell lines with a high FBS requirement, the use of HI-FBS or alternative toxicity assays can be considered, or the use of alternative formulations, such as chemically-defined serum-free media, be adopted.

A combinatorial biophysical approach; FTSA and SPR for identifying small molecule ligands and PAINs

Biophysical methods have emerged as attractive screening techniques in drug discovery both as primary hit finding methodologies, as in the case of weakly active compounds such as fragments, and as orthogonal methods for hit validation for compounds discovered through conventional biochemical or cellular assays. Here we describe a dual method employing fluorescent thermal shift assay (FTSA), also known as differential scanning fluorimetry (DSF) and surface plasmon resonance (SPR), to interrogate ligands of the kinase p38α as well as several known pan-assay interference compounds (PAINs) such as aggregators, redox cyclers, and fluorescence quenchers. This combinatorial approach allows for independent verification of several biophysical parameters such as KD, kon, koff, ΔG, ΔS, and ΔH, which may further guide chemical development of a ligand series. Affinity values obtained from FTSA curves allow for insight into compound binding compared with reporting shifts in melting temperature. Ligand-p38 interaction data were in good agreement with previous literature. Aggregators and fluorescence quenchers appeared to reduce fluorescence signal in the FTSAs, causing artificially high shifts in Tm values, whereas redox compounds caused either shifts in affinity that did not agree between FTSA and SPR or a depression of FTSA signal.

Differential interferences with clinical chemistry assays by gold nanorods, and gold and silica nanospheres

Nanomaterials are known to cause interference with several standard toxicological assays. As part of an in vivo study of PEG-coated gold nanorods in mice, nanorods were added to reference serum, and results for standard clinical chemistry parameters were compared with serum analyzed without nanorods. PEG-coated gold nanorods produced several concentration-dependent interferences. Comparisons were then made with PEG-coated gold and silica nanospheres. Interferences were observed for both materials that differed from gold nanorods. Removal of the particles from serum by centrifugation prior to analysis resolved most, but not all of the interferences. Additional clinical chemistry analyzers were used to further investigate trends in assay interference. We conclude that PEG-coated gold and silica nanoparticles can interfere with standard clinical chemistry tests in ways that vary depending upon material, shape, and specific assay methodology employed. Assay interferences by nanomaterials cannot always be predicted, underscoring the need to verify that nanomaterials under study do not interfere with methods used to evaluate potential biological effects.

Interference in autoanalyzer analysis

This paper presents certain simple procedures for assessing the most common types of interference, due to haemolysis, icterus or lipaemic serum in 19 routine Clinical Chemistry tests and suggests steps to overcome the problem in some tests. A change in the measured concentration, to be analytically significant, had to exceed 2.8 X % coefficient of variation (cv) of the intra-assay analytical variation of each assay. Haemolysis caused interference in 10 of the 19 assays investigated. A haemolysate haemoglobin concentration of 0.29 g/dl, visible to the eye, caused an analytically significant increase in creatinine kinase MB subunit (CKMB), lactate dehydrogenase (LDH), total protein, triglyceride, uric acid and urea, and a significant decrease in alkaline phosphatase (ALP), and total bilirubin. A higher concentration of haemoglobin (0.68 g/ dl) caused an additional significant increase in CK, and a decrease in direct bilirubin. Addition of bilirubin caused interference in all the peroxidase linked reactions as well as in the creatinine assay. At a serum concentration of 5.2 mg/dl it caused a decrease in creatinine, glucose, triglyceride and uric acid. At a higher concentration (15.9 mg/dl) it also decreased cholesterol. Lipaemia interference affected the least number of assays. An added triglyceride of 537-561 mg/dl caused an increase in glucose, uric acid, and amylase. At a level of 1122 mg/dl it also increased CKMB, and at a value of 2244 mg/dl it increased total and direct bilirubin. At the highest levels of haemolysis and lipaemia, the serum glutamate oxaloacetate transaminase (GOT) and giutamate pyruvate transaminase (GPT) gave erratic results. Overall uric acid and CKMB were the analytes most susceptible to interference, while serum caicium and phosphate did not suffer from any. The interference depends on the exact assay conditions used and the susceptibility of each individual laboratory's tests should be determined by them. The reasons for the interferences described are discussed.