The 99th percentile of reference population for cTnI and cTnT assay: Methodology, pathophysiology and clinical implications

According to recent international guidelines, including the 2012 Third Universal Definiton of Myocardial Infarction by the Joint ESC/ACCF/AHA/WHF Task Force, an increase in cardiac troponin (cTn) levels over the 99th percentile upper reference limit (99th URL) should be considered clinically relevant, this cut-off being measured with an imprecision â\u89¤10 CV%. In theory 99th URL values strongly depend not only on demographic and physiological variables (i.e. criteria for considering the reference population "healthy"), but also on the analytical performance of cTn methods and mathematical algorithms used for the calculation. The aim of the present article was therefore to review the methodological and pathophysiological factors affecting the evaluation and calculation of the 99th URL for cTn assay. The critical analysis made showed that no uniform procedure is followed, and nor have experts or regulatory bodies provided uniform guidelines for researchers or cTn assays manufacturers as an aid in "their quest to define normality". In particular, little attention has been paid to the way in which a healthy reference population is to be selected, or the criteria for calculating the 99th URL value for cTn assays, thus highlighting the need for international recommendations not only for demographic and physiological variables criteria for defining a healthy reference population, but also for calculating mathematical algorithms for establishing/calculating clinical decision values. An expert consensus group, comprising laboratory and clinical scientists, biomedical statisticians, industrial and regulatory representatives, should be responsible for drawing up these guidelines

Evaluation of analytical performance of a novel immunoenzymometric assay for cTnI

Letter to the Editor. We evaluated the analytical performance of the immunoenzymometric assay for the cTnI, named ST AIA-PACK cTnI 3rd-Gen, using the automated AIA-2000 platform (Tosoh Corporation, Tokyo, Japan). This method is a two-site immunoenzymometric assay, which uses a combination of two monoclonal antibodies, respectively directed to 41–49 and 87–91 amino acids of the cTnI peptide chain, and the ternary troponin ITC complex as a calibration antigen [1]

Multicentre comparison of BNP andNT-proBNP immunoassays: the CardioOrmocheck study

The present study demonstrates that there are marked differences in analytical characteristics and clinical results among the most popular commercial methods for BNP and NT-proBNP assay. As a result, clinicians should give great care to compare results obtained by different laboratories, expecially when different methods are used. Furthermore, our findings confirm that it is necessary a better standardization of immunoassay methods, expecially for BNP assay.Non disponibil

Systematic differences between BNP immunoassays: Comparison of methods using standard protocols and quality control materials

Background: Recent studies suggested that there are marked systematic differences among BNP immunoassays. In this study we compared the BNP data and clinical results obtained with different immunoassays, including a new method (ST-AIA-PACK, TOSOH Corporation). Methods: BNP was measured on plasma-EDTA samples of healthy subjects (HS, n = 126) and patients with heart failure (HF, n = 31 NYHA I, II; n = 46 NYHA III, IV) using the ST-AIA-PACK and the Triage Biosite (Beckman Coulter) methods. Control samples distributed in the CardioOrmoCheck external quality assessment were also measured with TOSOH and the most used BNP immunoassays in Italy. Results: TOSOH method showed a good correlation (R = 0.976; n = 327) but a mean bias (−46.9%) compared to Triage Biosite. On the base of the results obtained in 10 samples of the CardioOrmoCheck study, TOSOH method showed a strict agreementwith ADVIA Centaur, while it underestimated BNP in comparisonwith Triage (−52.5%) and ARCHITECT methods (−39.4%). The agreement of ST-AIA-PACK and Triage Biosite methods for classification of HF patients was tested using 100 ng/L of BNP; the positive agreement between methods was 65%, overall agreement was 73%. Conclusions: Our results confirm that there are marked differences in measured values among commercial methods for BNP assay

Stato dell’arte dell’immunodosaggio dei peptidi natriuretici di tipo B

State of the art of B-type natriuretic peptide (BNP) immunoassays. Recent studies have demonstrated that the precursor of BNP (proBNP) constitutes the major part of BNP-related peptides detectable in plasma of patients with heart failure by the commercially available immunoassays considered specific for the BNP hormone. Since proBNP significantly cross-reacts with commercial immunoassays for BNP, manufacturers should test and clearly declare the cross-reaction with proBNP in their BNP methods. Owing to the differences in cross-reaction with proBNP as well as in specificity, respectively, for the NH2- or COOH-terminal part of the peptide hormone chain, BNP immunoassays show significant between-method differences. Immunoassays for NT-proBNP, which all use standard materials and antibodies provided by the same company, show lower differences (generally <20%). Clinicians should take into account these differences among methods when they compare results obtained from different laboratories, which use different BNP immunoassays. Accordingly, the use of a common decisional limit for all BNP immunoassay methods, as suggested by the most recent international guidelines, may be unreliable

High molecular weight adiponectin is increased in plasma of patients with idiopathic dilated cardiomyopathy with and without overt heart failure

Purpose: Adiponectin, a biologically active substance with multimeric structure released by adipocytes, is considered as a new diagnostic/prognostic marker in the cardiovascular disease. The trimeric low-(LMW), the hexameric middle-(MMW) and the high-molecular weight (HMW) isoforms have been found in human peripheral circulation. It has been hypothesized that the HMW, that is an active form, has cardioprotective effects and its determination could give additional information on the role of this protein in cardiovascular diseases. Aim of the study was to determine the levels of adiponectin multimers in patients with dilated cardiomyopathy (DCM) and to evaluate its relationship with inflammatory profile and left ventricular (LV) function. Methods: The plasma levels of total (T) and adiponectin multimers were evaluated in 50 no diabetic patients with DCM (30 males, 38 in NYHA class I-II, 12 in NYHA class III, LVEF% 40.6?1.4, age 57?1 yrs, BMI 26.6?0.41 kg/m2, mean?sem) and in 25 age- and BMI-matched healthy subjects as controls. An Elisa system (Alpco Diagnostics, US) was used to directly measure T and, after treatment with two different specific proteases, the HMW and the sum of MMW and HMW forms while the levels of the MMW and LMW were obtained by difference. Results: T adiponectin in DCM increased with respect to controls as a function of disease severity (3.8?0.38 mg/ml vs 5.4?0.48 in NYHA class I-II vs 8.0?1.9 in NYHA class III; p<0.05 NYHA III vs controls and NYHA I-II) and correlated with functional and inflammatory indices. HMW was the predominant isoform in plasma, accounting for 50% of T adiponectin to which was positively correlated (p<0.001); MMW and LMW represented each the 25% of total protein. HMW significantly increased in DCM with respect to controls (1.8?0.15 mg/ml vs 2.5?0.21 in NYHA class I-II vs 4.8?1.2 in NYHA class III; p<0.001 NYHA III vs controls and NYHA I-II) while MMW and LMW did not vary with respect to controls or as a function of NYHA class. HMW correlated negatively with LVEF% (p=0.0041), positively with Interleukin-6 (p<0.001) and BNP (p=0.003). No significant correlation with BMI was observed both for total and HMW adiponectin. Conclusions: This study demonstrates that HMW adiponectin is elevated in DCM patients and increases significantly as a function of severity. Although many studies need to identify if the HMW isoform is associated to cardioprotection, the significant relation with markers of inflammation and cardiac dysfunction, lacking for MMW and LMW forms, underlines the importance to investigate the role of HMW in this disease

Head-to-head comparison of plasma cTnI concentration values measured with three high-sensitivity methods in a large Italian population of healthy volunteers and patients admitted to emergency department with acute coronary syndrome: A multi-center study

Abstract Background The study aim is to compare cTnI values measured with three high-sensitivity (hs) methods in apparently healthy volunteers and patients admitted to emergency department (ED) with acute coronary syndrome enrolled in a large multicentre study. Methods Heparinized plasma samples were collected from 1511 apparently healthy subjects from 8 Italian clinical institutions (mean age: 51.5 years, SD: 14.1 years, range: 18–65 years, F/M ratio:0.95). All volunteers denied chronic or acute diseases and had normal values of routine laboratory tests. Moreover, 1322 heparinized plasma sample were also collected by 9 Italian clinical institutions from patients admitted to ED with clinical symptoms typical of acute coronary syndrome. The reference study laboratory assayed all plasma samples with three hs-methods: Architect hs-cTnI, Access hs-cTnI and ADVIA Centaur XPT methods. Principal Component Analysis (PCA) was also used to analyze the between-method differences among hs-cTnI assays. Results On average, a between-method difference of 31.2% CV was found among the results of hs-cTnI immunoassays. ADVIA Centaur XPT method measured higher cTnI values than Architect and Access methods. Moreover, 99th percentile URL values depended not only on age and sex of reference population, but also on the statistical approach used for calculation (robust non-parametric vs bootstrap). Conclusions Due to differences in concentrations and reference values, clinicians should be advised that plasma samples of the same patient should be measured for cTnI assay in the same laboratory. Specific clinical studies are needed to establish the most appropriate statistical approach to calculate the 99th percentile URL values for hs-cTnI methods

Evaluation of 99th percentile and reference change values of a high-sensitivity cTnI method: A multicenter study

Abstract Background The Italian Society of Clinical Biochemistry (SIBioC) and the Italian Section of the European Ligand Assay Society (ELAS) have recently promoted a multicenter study (Italian hs-cTnI Study) with the aim to accurately evaluate analytical performances and reference values of the most popular cTnI methods commercially available in Italy. The aim of this article is to report the results of the Italian hs-cTnI Study concerning the evaluation of the 99th percentile URL and reference change (RCV) values around the 99th URL of the Access cTnI method. Materials and methods Heparinized plasma samples were collected from 1306 healthy adult volunteers by 8 Italian clinical centers. Every center collected from 50 to 150 plasma samples from healthy adult subjects. All volunteers denied the presence of chronic or acute diseases and had normal values of routine laboratory tests (including creatinine, electrolytes, glucose and blood counts). An older cohort of 457 adult subjects (mean age 63.0 years; SD 8.1 years, minimum 47 years, maximum 86 years) underwent also ECG and cardiac imaging analysis in order to exclude the presence of asymptomatic cardiac disease. Results and conclusions The results of the present study confirm that the Access hsTnI method using the DxI platform satisfies the two criteria required by international guidelines for high-sensitivity methods for cTn assay. Furthermore, the results of this study confirm that the calculation of the 99th percentile URL values are greatly affected not only by age and sex of the reference population, but also by the statistical approach used for calculation of cTnI distribution parameters

State of the art of immunoassay methods for B-type natriuretic peptides: An update

The aim of this review article is to give an update on the state of the art of the immunoassay methods for the measurement of B-type natriuretic peptide (BNP) and its related peptides. Using chromatographic procedures, several studies reported an increasing number of circulating peptides related to BNP in human plasma of patients with heart failure. These peptides may have reduced or even no biological activity. Furthermore, other studies have suggested that, using immunoassays that are considered specific for BNP, the precursor of the peptide hormone, proBNP, constitutes a major portion of the peptide measured in plasma of patients with heart failure. Because BNP immunoassay methods show large (up to 50%) systematic differences in values, the use of identical decision values for all immunoassay methods, as suggested by the most recent international guidelines, seems unreasonable. Since proBNP significantly cross-reacts with all commercial immunoassay methods considered specific for BNP, manufacturers should test and clearly declare the degree of cross-reactivity of glycosylated and non-glycosylated proBNP in their BNP immunoassay methods. Clinicians should take into account that there are large systematic differences between methods when they compare results from different laboratories that use different BNP immunoassays. On the other hand, clinical laboratories should take part in external quality assessment (EQA) programs to evaluate the bias of their method in comparison to other BNP methods. Finally, the authors believe that the development of more specific methods for the active peptide, BNP1–32, should reduce the systematic differences between methods and result in better harmonization of results

Clinical implications of a recent adjustment to the high-sensitivity cardiac troponin T assay: Some results

Letter to the Editor. Recently, some concerns have been reported about a technical bulletin by Roche Diagnostics GmbH (Mannheim, Germany) regarding the adjustment to the calibration curve of the Elecsys Troponin T high-sensitivity (hs) assay [1]. According to the bulletin, the goal of the manufacturer was to recalibrate the control materials of the Troponin T hs assays to return to the original assay specifications. The revised lots of calibrators (lots 167345 and 167650) should yield measurable cardiac troponin T (cTnT) concentrations in a greater proportion of patient samples for which the concentrations were undetectable with previous lots, including lot 163704 [1]. This adjustment regarding calibration materials may have major implication for patient care, including the recalculation of the 99th percentile value for cTnT assay [1], which is the cornerstone of the definition of myocardial infarction [2]. The aim of the present report is to compare the results obtained by measuring several plasma samples of healthy subjects and patients with acute or chronic cardiac diseases to give the users of Elecsys Troponin T hs assay some information on the difference in cTnT values measured using the previous and the new recalibrated lots