Retrospective clinical evaluation of 4 lateral flow assays for the detection of SARS-CoV-2 IgG

In a Clinical Laboratory Improvement Amendments laboratory setting, we evaluated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgG detection with 4 lateral flow immunoassays [LFIAs; 2 iterations from BTNX Inc. (n = 457) and 1 each from ACON Laboratories (n = 200) and SD BIOSENSOR (n = 155)]. In a cohort of primarily hospitalized, reverse-transcription polymerase chain reaction-confirmed coronavirus disease 2019 cases, sensitivity at ≥14 days from symptom onset was: BTNX kit 1, 95%; BTNX kit 2, 91%; ACON, 95%; and SD, 92%. All assays showed good concordance with the Abbott SARS-CoV-2 IgG assay at ≥14 days from symptom onset: BTNX kit 1, 99%; BTNX kit 2, 94%; ACON, 99%; and SD, 100%. Specificity, measured using specimens collected prior to SARS-CoV-2 circulation in the United States and "cross-reactivity challenge" specimens, was 98% for BTNX kit 1 and ACON and 100% for BTNX kit 2 and SD. These results suggest that LFIAs may provide adequate results for rapid detection of SARS-CoV-2.

Evaluating Tiered Hemolysis Thresholds to Facilitate Rapid Reporting of High-Sensitivity Cardiac Troponin

Background

Cardiac troponin (cTn) assays are used for the diagnosis of acute myocardial infarction and frequently require serial measurements. Recollection of unacceptable specimens for hemolysis can delay results and disrupt timing of serial measurements. This study was designed to assess the influence of hemolysis on a high-sensitivity cTnT assay in granular detail at clinically important concentrations. These were used in consultation with the clinical practice to evaluate risk-based thresholds for acceptable amounts of hemolysis.

Methods

Plasma pools ranging from <10 to >100 ng/L cTnT were spiked with hemolysate to various degrees of hemolysis and measured using the Elecsys Troponin T Gen 5 STAT assay. The impact of accepting expanded hemolysis thresholds was completed using retrospective data of 12225 serial cTnT results and an additional 4651 baseline cTnT results.

Results

The mean percent change in cTnT was consistent for a given degree of hemolysis regardless of the initial nonhemolyzed cTnT concentration. Tiered hemolysis thresholds were evaluated for low-risk patients (apparent cTnT ≤8 ng/L), intermediate-risk patients (thresholds for 9–37 ng/L, 38–66 ng/L, and 67–99 ng/L cTnT), and high-risk patients (≥100 ng/L cTnT). The influence of tiered hemolysis thresholds was calculated for patients with serial (0 and 2 h) cTnT results, which demonstrated that the majority of 2-h delta interpretations were unchanged. Implementation of tiered thresholds dramatically decreased recollections for hemolyzed cTnT samples.

Conclusion

Tiered hemolysis cutoffs minimized disruption to patient care for low- and high-risk patients, while maintaining the integrity of serial measurements for those with intermediate cTnT concentrations.

False-positive amphetamine results on several drug screening platforms due to mexiletine

OBJECTIVE

False-positive urine drug of abuse screening (UDS) results can have serious implications in clinical practice, particularly when confirmation assay results are not immediately available to providers making medical decisions. Often it is not possible to identify the specific medication or other interfering compound that is responsible for the false-positive UDS result. Even when a potential interference is reported in the literature or package insert for one assay, the applicability to other UDS platforms/assays is often unknown. Mexiletine has been suggested as a cause of false-positive amphetamine results, but never confirmed as the causative agent in previous reports. The goal of this study was to confirm this drug as a cross-reacting compound in amphetamine screening tests.

METHODS

We evaluated several amphetamine screening assays: the Syva EMIT II Plus and the Roche KIMS automated immunoassays, along with the Noble Split-Specimen and Synchron QuikScreen point-of-care assays.

RESULTS

Urine samples from two patients treated with mexiletine were positive on all amphetamine screens but confirmed negative by mass spectrometry. Drug-free urine spiked with mexiletine caused positive results on all assays, although the EMIT II Plus and KIMS assays cross-reacted at lower mexiletine concentrations than the point-of-care assays.

CONCLUSION

This report confirms that mexiletine can cross-react on several amphetamine screening assays. Assay manufacturers are encouraged to evaluate mexiletine cross-reactivity, and providers and laboratories should be aware of the potential for false-positive amphetamine screening results in patients taking mexiletine.

Genetic variation in statin intolerance and a possible protective role for UGT1A1

The etiology of statin intolerance is hypothesized to be due to genetic variants that impact statin disposition and clearance. We sought to determine whether genetic variants were associated to statin intolerance. The studied cohort consisted of hyperlipidemic participants (n = 90) clinically diagnosed with statin intolerance by a cardiologist and matched controls without statin intolerance. Creatine kinase activity, lipid profiles and genetic analyses were performed on genes involved in statin metabolism and included UGT1A1 and UGT1A3 sequencing and targeted analyses of CYP3A4*22, CYP3A5*3, SLCO1B1*5 and *1b, ABCB1 c.3435C>T, ABCG2 c.421C>A and GATM rs9806699. Although lipids were higher in cases, genetic variant minor allele frequencies were similar between cases and controls, except for UGT1A1*28, which was less prevalent in cases than controls.

Neonatal Intensive Care Unit Quality Initiative: Identifying Preanalytical Variables Contributing to Specimen Hemolysis and Measuring the Impact of Evidence-Based Practice Interventions

OBJECTIVES

Blood specimen hemolysis is a major cause of sample recollection in the neonatal intensive care unit. We aimed to reduce the hemolysis rate from 6.3% at baseline to less than 4% within the 9 months' duration of the study.

METHODS

Intravenous infusion of lipid emulsion during sample collection, sample collection site, and blood sample transportation methods were investigated as possible contributors to hemolysis. Subsequently, two practice improvements were implemented: pausing lipid emulsion infusion prior to collection and slowing withdrawal rates through arterial catheters.

RESULTS

Samples were more likely to be hemolyzed if they were collected during lipid infusion and subsequently transported by pneumatic tube or collected through an arterial catheter. Retrospective analysis demonstrated a decreased number of tests cancelled due to specimen hemolysis (3.5%) after our interventions.

CONCLUSIONS

We identified three variables contributing to hemolysis and instituted two clinical practice interventions to significantly reduce test cancellations due to hemolysis.

Label-free detection and identification of protein ligands captured by receptors in a polymerized planar lipid bilayer using MALDI-TOF MS

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) coupled with affinity capture is a well-established method to extract biological analytes from complex samples followed by label-free detection and identification. Many bioanalytes of interest bind to membrane-associated receptors; however, the matrices and high-vacuum conditions inherent to MALDI-TOF MS make it largely incompatible with the use of artificial lipid membranes with incorporated receptors as platforms for detection of captured proteins and peptides. Here we show that cross-linking polymerization of a planar supported lipid bilayer (PSLB) provides the stability needed for MALDI-TOF MS analysis of proteins captured by receptors embedded in the membrane. PSLBs composed of poly(bis-sorbylphosphatidylcholine) (poly(bis-SorbPC)) and doped with the ganglioside receptors GM1 and GD1a were used for affinity capture of the B subunits of cholera toxin, heat-labile enterotoxin, and pertussis toxin. The three toxins were captured simultaneously, then detected and identified by MS on the basis of differences in their molecular weights. Poly(bis-SorbPC) PSLBs are inherently resistant to nonspecific protein adsorption, which allowed selective toxin detection to be achieved in complex matrices (bovine serum and shrimp extract). Using GM1-cholera toxin subunit B as a model receptor-ligand pair, we estimated the minimal detectable concentration of toxin to be 4 nM. On-plate tryptic digestion of bound cholera toxin subunit B followed by MS/MS analysis of digested peptides was performed successfully, demonstrating the feasibility of using the PSLB-based affinity capture platform for identification of unknown, membrane-associated proteins. Overall, this work demonstrates that combining a poly(lipid) affinity capture platform with MALDI-TOF MS detection is a viable approach for capture and proteomic characterization of membrane-associated proteins in a label-free manner.

Quantitation of 1α,25-dihydroxyvitamin D by LC-MS/MS using solid-phase extraction and fixed-charge derivitization in comparison to immunoextraction

The objective of this study was to present analysis of 1α,25-dihydroxyvitamin D (DHVD) by solid-phase extraction (SPE) using fixed-charge derivitization extraction to enhance ionization for liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) in comparison to traditional immunoextraction (IE) techniques.

Full analytical validation of both a SPE and IE LC-MS/MS assay was performed, and included accuracy, intra- and inter-assay precision, limit of detection and limit of quantitation. Performance of these two assays was compared with reference laboratory IE LC-MS/MS testing.

This SPE LC-MS/MS assay demonstrated similar performance to the IE LC-MS/MS assay validated simultaneously. Intra-assay precision for low (12 pg/mL), medium (25 pg/mL) and high (60 pg/mL) control samples was 7.2%, 13.7% and 11.3% for DHVD2, respectively, and 9.1%, 5.9% and 8.9% for DHVD3. The inter-assay precision was 11.6%, 10.3% and 3.9% for DHVD2 and 10.6%, 7.0% and 5.6% for DHVD3. The limit of detection was 1.9 and 2.7 pg/mL for DHVD2 and DHVD3, and limit of quantitation was 4 pg/mL for both DHVD2 and DHVD3. Comparison to a reference LC-MS/MS assay showed excellent correlation (slope 0.936, R

The study demonstrated comparability of the SPE-LC-MS/MS assay for analysis of DHVD and offers an attractive option for assessment of vitamin D status as an alternative to traditional IE techniques.

CEA, AFP and CA 19-9 analysis in peritoneal fluid to differentiate causes of ascites formation

OBJECTIVES

Tumor marker analysis in ascites has been proposed as a measure to aid in the diagnosis of malignancy. The objectives of this study were to establish tumor marker cut-offs and determine the diagnostic performance of measuring CEA, CA 19-9 and AFP in ascites for differentiating between non-malignant and malignant etiologies.

DESIGN AND METHODS

Ascites from 137 patients (83 non-malignant, 54 malignant) was assayed for CEA, CA 19-9 and AFP concentrations by immunoassay. Diagnostic cut-offs were established via ROC curve analysis. Performance was compared to cytology findings and patient history following medical chart review. Analysis based on cytological findings in combination with tumor marker testing, as well as subset analysis by tumor marker secretion was also performed.

RESULTS

Concentrations of CEA, CA 19-9 and AFP were significantly higher in patients with malignant ascites versus non-malignant etiologies. The diagnostic cut-off, sensitivity and specificity for CEA were 3.5 ng/mL, 31% and 95%, respectively; for CA 19-9 were 72 U/mL, 30% and 95%; and for AFP were 5 ng/mL, 17% and 95%. Using cytological findings in conjunction with tumor marker results improved the sensitivity of CEA, CA 19-9 and AFP to 57.4%, 64.8%, and 59.3%, respectively. Improvement in sensitivity was seen when subset analysis by causative malignancy was performed.

CONCLUSIONS

Tumor marker analysis in ascites, especially in subset analysis by type of malignancy, demonstrated utility for differentiating non-malignant from malignant etiologies. This analysis should not replace cytology, but offers potential for differentiation in situations where cytology is inconclusive, or in patients with suspected malignancies known to secrete these markers.

Development of a host blood meal database: de novo sequencing of hemoglobin from nine small mammals using mass spectrometry

We report the successful de novo sequencing of hemoglobin using a mass spectrometry-based approach combined with automatic data processing and manual validation for nine North American species with currently unsequenced genomes. The complete α and β chain of all nine mammalian hemoglobin samples used in this study were successfully sequenced. These sequences will be appended to the existing database containing all known hemoglobins to be used for identification of the mammalian host species that provided the last blood meal for the tick vector of Lyme disease, Ixodes scapularis.

PCR-electrospray ionization mass spectrometry: the potential to change infectious disease diagnostics in clinical and public health laboratories

During the past 20 years, microbial detection methods that are genetically based, such as real-time PCR and peptide nucleic acid fluorescent hybridization, coexisted with traditional microbiological methods and were typically based on the identification of individual genetic targets. For these methods to be successful, a potential cause of infection must be suspected. More recently, multiplex PCR and multiplex RT-PCR were used to enable more broad-range testing based on panels of suspected pathogens. PCR–electrospray ionization mass spectrometry (PCR-ESI/MS) has emerged as a technology that is capable of identifying nearly all known human pathogens either from microbial isolates or directly from clinical specimens. Assay primers are strategically designed to target one or more of the broad pathogen categories: bacterial, mycobacterial, fungal, or viral. With broad-range amplification followed by detection of mixed amplicons, the method can identify genetic evidence of known and unknown pathogens. This unique approach supports a higher form of inquiry, asking the following question: What is the genetic evidence of known or unknown pathogens in the patient sample? This approach has advantages over traditional assays that commonly target the presence or absence of one or more pathogens with known genetic composition. This review considers the breadth of the published literature and explores the possibilities, advantages, and limitations for implementation of PCR-ESI/MS in diagnostic laboratories.

Comparative analysis of PCR-electrospray ionization/mass spectrometry (MS) and MALDI-TOF/MS for the identification of bacteria and yeast from positive blood culture bottles

BACKGROUND

Emerging technologies for rapid identification of microbes demonstrate a shift from traditional biochemical and molecular testing algorithms toward methods using mass spectrometry (MS) for the semiquantitative analysis of microbial proteins and genetic elements. This study was performed to assess the diagnostic accuracy of 2 such technologies, PCR–electrospray ionization (ESI)/MS and MALDI-TOF/MS, with respect to phenotypic and biochemical profiling as a reference standard method. A positive challenge set of blood culture bottles was used to compare PCR-ESI/MS and MALDI-TOF/MS performance on a matched set of samples.

METHODS

We performed characterization of bloodstream infections from blood cultures using the Ibis T5000 PCR-ESI/MS and the Bruker MALDI Biotyper 2.0 (MALDI-TOF/MS) platforms for microbial identification. Diagnostic accuracy was determined by independent comparison of each method to phenotypic and biochemical characterization with Vitek2 analysis as the reference standard identification.

RESULTS

The diagnostic accuracy, represented as positive agreement, at the genus level was 0.965 (0.930–0.984) for PCR-ESI/MS and 0.969 (0.935–0.987) for MALDI-TOF/MS, and at the species level was 0.952 (0.912–0.974) with PCR-ESI/MS and 0.943 (0.902–0.968) for MALDI-TOF/MS. No statistically significant difference was found between PCR-ESI/MS and MALDI-TOF/MS in the ability to rapidly identify microorganisms isolated from blood culture.

CONCLUSIONS

Our results demonstrate that PCR-ESI/MS and MALDI-TOF/MS are equivalent in their ability to characterize bloodstream infections with respect to the reference standard, and highlight key differences in the methods that allow for each method to have a unique niche as a tool for rapid identification of microbes in blood cultures.