Jill Tate

Characterisation of a highly sensitive troponin I assay and its application to a cardio-healthy population.

Abstract Background: Abbott Diagnostics have developed a new highly sensitive troponin I (hs-TnI) assay. We have assessed its analytical characteristics and applied the assay to a population of apparently cardio-healthy persons. Methods: We assessed imprecision, bias compared to the previous generation assay, matrix effects, and interferences and applied the assay to an apparently healthy population, deriving the 99th percentile limit of the distribution of values in reference populations for men and women separately. Results: The dynamic range of the assay was ranged from 0.5–50,000 ng/L (pg/mL). The 10% CV was at a concentration of 3.9 ng/L, and the 20% CV was at a concentration of 1.8 ng/L. The new and current version of the TnI assay were highly correlated [slope: 0.98 (95%CI:0.88–1.07), y-intercept:1.20 (95%CI:-2.35–4.75) r2=0.99]. The 99th percentile limit of the distribution of values in a reference population was different for males and females: for males 14.0 ng/L and for females 11.1 ng/L and at these concentrations the assay CV was 5.0%. TnI was detectable in nearly all patient samples from the healthy reference population (98.6%). Conclusions: This new hs-TnI assay is able to measure to an order of magnitude lower than the current generation TnI assay from the same manufacturer. With TnI being detectable in nearly all apparently healthy subject samples this suggests that TnI presence does not always indicate cardiomyocyte necrosis.

An erythrocyte transketolase isoenzyme pattern associated with the Wernicke-Korsakoff syndrome.

Abstract. Two techniques were used to seek variants of human erythrocyte transketolase and to test for any association of the Wernicke‐Korsakoff syndrome, a thiamin‐deficiency disease, with a particular variant of this thiamin‐dependent enzyme. Apparent Km values for the cofactor thiamin diphosphate were similar for patients and controls. However, isoelectric focussing separated erythrocyte transketolase into different isoenzymes characterized by pI values in the range 6·6–9·2. Six distinct patterns of isoenzymes were found in thirty‐six healthy control subjects. The isoenzyme pattern for thirty‐nine out of forty‐two patients suffering from the Wernicke‐Korsakoff syndrome was identical to a pattern found in only eight of thirty‐six control subjects, a highly significant association (P < 0·001). This association suggests that a variant transketolase and thiamin deficiency together contribute to the pathogenesis of the brain damage of the Wernicke‐Korsakoff syndrome by some mechanism independent of apparent Km values for thiamin diphosphate.

Evaluation of the N Latex FLC free light chain assay on the Siemens BN analyser: precision, agreement, linearity and variation between reagent lots.

Background The clinical utility of serum κ and λ free light chains (FLC) for the diagnosis and prognosis of plasma cell proliferative disorders is well established. We assessed the analytical performance of the N Latex FLC assays and compared it with the Freelite™ assays. Methods Analytical precision was assessed according to the CLSI EP5-A2 protocol. Method comparison was performed with 116 clinical samples and linearity was assessed on samples with monoclonal and polyclonal elevations of FLC. Analytical bias and variance was measured with two lots of N Latex FLC reagent. Results The N Latex FLC κ and λ assays had a total coefficient of variation of 5–7% across the analytical range. The slopes were 1.36 and 1.37 and the between-method variances were 40.0% and 45.4%, respectively, compared with the Freelite™. Good agreement in classification was observed for κ, λ and the κ/λ ratio (Cohens κ 0.84, 0.76 and 0.89). Statistical non-linearity occurred commonly, but clinically significant non-linearity was observed in only one instance. Between-reagent lot variation was 7.3% and 10% for κ and λ, respectively. Conclusions The N Latex FLC assay has good precision, did not exhibit gross antigen excess and can be used in clinical practice based on the analytical performance characteristics.

ELF score ≥9.8 indicates advanced hepatic fibrosis and is influenced by age, steatosis and histological activity

There is increasing need to identify individuals with advanced liver fibrosis, who are at risk of complications such as hepatocellular carcinoma. The commercially available enhanced liver fibrosis (ELF) test provides a non‐invasive assessment of fibrosis severity. This study was designed to determine the diagnostic accuracy of the manufacturers cut‐off value (≥9.8) in identifying advanced fibrosis.

Evaluation of the N Latex free light chain assay in the diagnosis and monitoring of AL amyloidosis.

Abstract Background: We compared a novel assay for free light chain (FLC) quantitation based on monoclonal antibodies (N-Latex, Siemens, Germany) to the established polyclonal antibody-based assay (Freelite™, The Binding Site, UK) in AL amyloidosis. Methods: Sixty-two diagnostic samples were analysed on a BNII nephelometer, 32 of which also had a post-treatment sample. Results: In the diagnostic samples: for AL of κ type, the median involved FLC (iFLC) was significantly lower by the N-Latex assay (289 vs. 667 mg/L, p=0.0002) whereas for λ AL the values were similar (148 vs. 161 mg/L, p=0.84). Measurable disease, defined as a difference between involved and uninvolved FLC (dFLC) >50 mg/L was present in 82% by the N-Latex assay compared to 89% by the Freelite™ assay. For diagnostic sensitivity, the FLC ratio was normal in 21% (95% CI 12%–33%) and 15% (95% CI 7%–26%) of patients by the N-Latex and Freelite™ assays, respectively. The combination of serum and urine immunofixation electrophoresis with either FLC assay allowed identification of the amyloidogenic clone in 98% producing comparable sensitivity. For the monitoring samples the median reduction in dFLC was 68% for the N-Latex assay and 77% for the Freelite™ assay (p=0.04). This led to some differences in assigning response categories. Partial response as assigned by both assays predicted overall survival (N-Latex p=0.0015, Freelite™ p=0.022). Conclusions: There are differences between FLC as measured by the N-Latex and Freelite™ assays, but overall the two assays have similar diagnostic sensitivity. Disease response calculated by both assays predicts survival but more clinical validation is required.

Borderline High Serum Free Light Chain κ/λ Ratios Are Seen Not Only in Dialysis Patients but Also in Non–Dialysis-Dependent Renal Impairment and Inflammatory States

We read with interest the article by Abadie et al1 and would like to add our observations that largely corroborate their findings. Abadie et al1 provide confirmatory data that renal reference intervals are required when interpreting the serum free light chain (FLC) ratio in patients suspected of having plasma cell dyscrasias. Because borderline ratios cause significant diagnostic confusion, we were interested to further characterize the clinical characteristics of patients who had borderline abnormal serum FLC ratios and no evidence of plasma cell dyscrasias or lymphoproliferative disorders. We performed a retrospective audit of FLC assays performed between January 1, 2006, and September 13, 2008, at 3 tertiary referral hospitals and correlated cases with borderline abnormal ratios (arbitrarily defined as 0.13–0.25 and 1.66–3.2, ie, 2 times …

Combined light chain immunofixation to detect monoclonal gammopathy: a comparison to standard electrophoresis in serum and urine

Abstract Background: The purpose of this study was to evaluate a combined κ and λ light chain immunofixation (CLIF) as a screening tool to detect monoclonal immunoglobulins in serum and urine. A secondary aim was to investigate the impact on workflow and reagent utilisation of a systematic implementation of CLIF in addition to routine protein electrophoresis (PE) on all samples. Methods: Light chain antisera (κ and λ) were mixed in a 1:1 ratio and loaded in the same sequence as the PE to create a superimposable image. Results: The CLIF procedure agreed significantly better with standard immunofixation procedures in the serum and urine. In 33 (22%) new patients and in 114 (15%) follow-up patients CLIF detected a band missed by PE in serum. In 34 (4.5%) of previously categorised cases the monoclonal band was below the detection limit of CLIF in serum, but still detectable by conventional immunofixation electrophoresis. In one case (0.7%) a band in a urine specimen was missed by CLIF compared to 70 (49%) missed by PE. After the systematic introduction of CLIF turn-around-times (TATs) and utilisation of laboratory consumables decreased significantly (p<0.001). Conclusions: A systematic implementation of CLIF led to the detection of monoclonal bands missed by PE with an improvement in TATs and a decrease in cost.

Comparison of Freelite™ and N Latex serum free light chain assays in subjects with end stage kidney disease on haemodialysis

Abstract Background: Quantification of serum free light chains (FLC) is important in the diagnosis of plasma cell diseases where an abnormal kappa:lambda ratio infers a population of monoclonal plasma cells. The Freelite™ and N Latex assays have been validated in populations without kidney disease but there is a paucity of data relating to the use of these assays in end stage kidney disease (ESKD). The aim of the study was to compare FLC assay performance in ESKD patients on haemodialysis. Methods: Cross-sectional multi-centre study comparing the performance of the two assays on 112 haemodialysis patients without known paraproteinaemia. We quantified FLC pre- and post-dialysis using both the N Latex and the Freelite assays. Results: FLC levels were elevated by both assays. Lambda FLC levels were considerably higher by the N Latex assay. Using the proposed renal reference range for Freelite (0.37–3.1) all but one patient had normal kappa:lambda FLC ratios. In contrast, there were no abnormal FLC ratios pre-dialysis using the N Latex assay. This was due to lambda FLC reading significantly higher by the N Latex assay. Kappa and lambda FLC levels decreased with dialysis but remained elevated above the normal range. The excess of lambda FLC by N Latex persisted post-dialysis but was somewhat attenuated. Dialysis adequacy and dialysis modality predicted clearance of kappa and lambda FLC by both assays. Conclusions: The N Latex assay reported significantly higher pre-dialysis lambda FLC concentrations compared with the Freelite assays. Clinicians should be aware of the need for a separate renal reference range for interpreting FLC ratio using the Freelite assay but not for the N Latex assay in ESKD patients.

Scientific publishing in the “predatory” era

Publishing is the core of scientific research, allowing the dissemination of important findings, either negative or positive, in the scientific community. Publication of articles is also the core of a scientific curriculum, as it provides an objective means for the assessment regarding academic progression, for funding applications and benchmarking of individual scientists, universities or other scientific institutions [1]. The possible criteria related to scientific publishing that can be used for evaluation include the overall number of articles published by the scientist (throughout the entire scientific career or within a given period of time) along with the impact of published research on scientific community, both in terms of impact factor (IF) of the journal where the articles are published and the overall number of citations to these articles [2]. The use of these so-called “bibliometric indices” has contributed to enormously boosting scientific publishing in recent years, and has also been associated with the birth of a kaleidoscope of new scientific journals, targeting almost each specialty, sub-specialty and even micro-specialty of science and medicine, including, last but not least, clinical biochemistry and laboratory medicine. Currently, in this continuously evolving scenario, even the more skilled scientist may be in trouble finding a way out through dozens of potential scientific journals to which articles may be submitted. Although this commentary is not intended to make the rules, but should be mostly regarded as a personal view of the authors, it is our intention to delineate some indicators that may be helpful in guiding scientists in the accurate selection of a journal. The first and probably most important issue is whether or not the journal is indexed by distinguished and wellrecognized scientific databases. These typically include Medline (with its interface PubMed), Scopus/EMBASE and the Web of Science. Unlike other scientific platforms such as Google Scholar, these influential biomedical search engines are characterized by high accuracy, as all entries are accurately scrutinized and monitored over time [3]. Moreover, the main criteria used for a scientist’s evaluation (overall IF, Hirsh-index [h-index], overall number of citations) are typically retrieved from Scopus (and, occasionally, from the Web of Science), as this platform cannot be artificially inflated by authors due to the presence of the so-called “unique identifier”, which corresponds to the ORCID (Open Researcher and Contributor ID) [4]. Conversely, an author can easily claim authorship of an article published by other authors (with the same name) in Google Scholar by simply adding it to his/her profile, which would then unethically boost the h-index and citations. This is probably why Google Scholar metrics are not used as scientific indicators by some scientific academic organizations. Conversely, publishing an article in journals indexed in Medline, Scopus/EMBASE and the Web of Science gives a much stronger guarantee that this publication will then translate into measurable benefits for the scientific curriculum. A second important aspect is the need to pay submission/publication fees to the publisher, in most cases for the so-called “open-access” option, which allows full text accessibility without subscription to the journal. Albeit this opportunity is indeed beneficial for many scientists, as open-access articles usually allow deeper percolation of knowledge, enhanced accessibility and a higher number of citations, it is not always clear whether this policy only shifts the invoice for journal production from the reader to the author with no change in overall quality criteria or whether it is a business model based on pay per publication [5]. Perhaps, we should remember that in the past articles in US journals which charged the author, e.g. the Proceedings of the National Academy of Sciences had to be labelled as “advertisement”. While many of us perceived this as odd, the current developments prove that there was a good reason for this regulation. Basically, we are not against open-access publishing, as long as quality of the individual article rather than payment of a publication fee is the main criterion for acceptance. This means that the quality criteria, in particular the peer review process, and consequently the good reputation of the publisher, should be the cornerstone for the decision to publish under an open-access agreement. This leads us to the third important aspect, which actually causes a number of ethical issues, i.e. the receipt of unsolicited, bizarre e-mails, beginning with “Hello

COMPARISON OF HIGHLY SENSITIVE TROPONIN I AND T RESULTS IN THE DIAGNOSIS OF ACUTE MYOCARDIAL INFARCTION

The performance of highly sensitive troponin assays in the early detection of acute myocardial infarction (AMI) in patients presenting to the emergency department (ED) with chest pain is assay-dependent. The aim was to compare the diagnostic accuracy for AMI of highly sensitive troponin I (hsTnl)