Analytical performance and clinical results of a fully automated MEIA system for brain natriuretic peptide assay: comparison with a point of care testing method

Significant discordance between point of care BNP values obtained by the i-STAT and the Beckman DXI 800, causing confusion in patient management when both methods are used interchangeably by clinicians

B-type natriuretic peptide (BNP) is used as a biomarker of heart failure. In our hospital point of care (POCT) BNP test is performed in EDTA whole blood using i-STAT (Abbott Laboratories, Abbott Park, IL, USA) and in the clinical laboratory using EDTA plasma and the DXI 800 analyzer (Beckman, Brea, CA, USA). We compared BNP values in 88 patients obtained by using the i-STAT followed by using the DXI 800. The time difference between the two analyses varied from 32 min to less than 12 h. In addition, 11 specimens were simultaneously analyzed for BNP using both the i-STAT and the DXI 800 analyzer. Plotting BNP concentrations obtained by the DXI 800 in the x-axis (reference method) and the i-STAT values in the y-axis, we observed the following regression equation; y = 1.4758 x + 23.452 (n = 88, r = 0.96), indicating significant positive bias with the i-STAT. In addition, we also observed significant differences between BNP values obtained by the i-STAT and the DXI 800 in 11 specimens analyzed simultaneously. Therefore, clinicians should not use BNP concentrations obtained by the i-STAT interchangeably with BNP concentrations obtained by the DXI 800 analyzer for patient management.

New issues on measurement of B-type natriuretic peptides

The measurement of the active hormone of B-type natriuretic peptide (BNP) system actually has several analytical limitations and difficulties in clinical interpretations compared to that of inactive peptide N-terminal proBNP (NT-proBNP) because of the different biochemical and pathophysiological characteristics of two peptides and quality specifications of commercial immunoassay methods used for their measurement. Because of the better analytical characteristics of NT-proBNP immunoassays and the easier pathophysiological and clinical interpretations of variations of NT-proBNP levels in patients with heart failure (HF), some authors claimed to measure the inactive peptide NT-proBNP instead of the active hormone BNP for management of HF patients. The measurement of the active peptide hormone BNP gives different, but complementary, pathophysiological and clinical information compared to inactive NT-proBNP. In particular, the setup of new more sensitive and specific assays for the biologically active peptide BNP1-32 should give better accurate information on circulating natriuretic activity. In conclusion, at present time, clinicians should accurately consider both the clinical setting of patients and the analytical characteristics of BNP and NT-proBNP immunoassays in order to correctly interpret the variations of natriuretic peptides measured by commercially available laboratory methods, especially in patients treated with the new drug class of angiotensin receptor-neprilysin inhibitors.

Falsely high B-type natriuretic peptide concentration in patients without heart failure attributed to AxSYM assay: case series of eight subjects

We report a case series of eight subjects complaining of non‐specific chest pain without heart failure, but with apparent high concentrations of plasma B‐type natriuretic peptide (BNP). No positive clinical characteristics were identified in physical examinations, cardiac imaging, laboratory findings, or pulmonary function tests. However, we observed unusually high BNP values when analysing blood samples of the patients using the AxSYM assay, and this was not supported by readings from Triage® or ADVIA Centaur® assays on the same samples, which showed BNP within the normal range. We believe that the possibility for false readings for high BNP levels in healthy individuals measured by AxSYM assay should be taken into account by physicians in clinical practice to avoid medical errors.

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.

Equal performance of novel N-terminal proBNP (Cardiac proBNP®) and established BNP (Triage BNP®) point-of-care tests

Background: Recently, a novel point-of-care test (POCT) for N-terminal proBNP (NTproBNP) has been introduced (Cardiac proBNP®, Roche). Aim: The aim was to compare the novel POCT for NTproBNP with the established POCT for BNP. Methods: NTproBNP and BNP were assessed in 222 individuals with chronic heart failure (n = 151) or controls (n = 71) with both POCTs. Results: NTproBNP and BNP were closely correlated upon regression analysis (r = 0.93; p < 0.01). NTproBNP and BNP were both correlated with ejection fraction and New York Heart Association stage. Receiver operating characteristic analysis yielded satisfying and equivalent predictive values for the detection of left ventricular dysfunction (ejection fraction <40%; NTproBNP: area under the curve 0.97; BNP: area under the curve 0.96; p > 0.05) and presence of New York Heart Association stage >2 (area under the curve 0.92 vs 0.91 for NT-proBNP and BNP, respectively; p > 0.05). Conclusion: The NTproBNP POCT allows biochemical detection of heart failure with satisfactory predictive values, is equivalent to the BNP POCT and will improve near-patient testing.

Cardiovascular biomarkers: increasing impact of laboratory medicine in cardiology practice

The practice of cardiology is in continual evolution, in parallel with the progress achieved by medical research in understanding the pathophysiology of cardiovascular disease and in developing new therapeutic procedures. Consequently, manufacturers of cardiac biomarkers are pressed with new demands to improve the performance of the existing and the development of novel ones. Several highly sensitive and/or specific assays for myocardial ischemic damage and myocardial function detection have already become commercially available. Moreover, an increasing number of novel risk factors have been added to the classical risk factors of cardiovascular disease. Finally, the recent surge of genetic analysis procedures will likely soon provide the clinical cardiologist with a number of laboratory tests for defining the molecular diagnosis, assessing new risk factors, and better targeting the pharmaceutical approaches in patients with cardiovascular disease. In this review, we first present the general characteristics of a biomarker followed by the analytical and clinical performance of assay methods.

The use of biomarkers for the evaluation and treatment of patients with acute coronary syndromes

The advent of inexpensive, highly accurate, and predictive markers of myocardial injury, inflammation, and hemodynamic stability has revolutionized the evaluation and treatment of patients who have acute coronary syndromes (ACSs). These blood biomarkers require small sample volumes, can be run expeditiously, and provide important information concerning the diagnosis, risk stratification, and treatment of these patients. To understand the use of these markers, one must have some knowledge about what elevations in these markers imply, how they have to be collected and measured to provide reliable information, when to suspect analytic confounds, and what the key values are that impart the diagnostic, prognostic, and therapeutic information. This article discusses these issues, emphasizing what clinicians must know for optimal test use, and then addresses the practical use of these markers in patients who have ACS.

The importance of analytical quality specifications for biomarker assays currently used in acute cardiac care

It is very important that cardiac biomarkers on which clinically relevant decisions will rest are measured with highly reliable assays. Adequate studies are needed before new methods can be implemented in the laboratory routine, and only well-documented assays should be considered for clinical use. Therefore, it is critical that, as new biomarkers are proposed, quality specifications are developed. Only after appropriate analytical quality specifications are addressed, the issues pertaining to methodological differences that result in non-harmonized concentration values, and clinical interpretation of biomarker concentrations will be reconciled. Today, the technology to address many analytic problems is at hand, but commitment on the part of manufacturers and their customers in the laboratory and clinical communities is essential. The design control loop is not closed until the finished in vitro diagnostic system is adequately validated to meet the customer needs, including analytical quality specifications. It is essential to determine the attributes and performance characteristics of relevant competitive systems and their degree of acceptance by clinical laboratories in order to demonstrate that user needs are definitely met. The responsibility of defining and implementing these issues must be a shared responsibility among laboratorians, clinicians, industry, and regulatory agencies on an international front. To date, two sets of quality specifications have been published, one for cardiac troponin assays and one for B-type natriuretic peptide assays. Both address analytical factors, such as calibrator characterization, antibody specificity, assay sensitivity and imprecision, and interferents, as well as preanalytical factors, such as sample type and stability. It would be ideal if regulatory agencies, such as FDA in the United States, accept these criteria for premarket approval clearance applications.

Rapid brain natriuretic peptide test and Doppler echocardiography for early diagnosis of mild heart failure

BACKGROUND

The early identification of patients at risk for the development of clinical heart failure (HF) is a new challenge in an effort to improve outcomes.

METHODS

We prospectively evaluated whether the combination of brain natriuretic peptide (BNP) measurements (Triage BNP test, Biosite Diagnostics) and echocardiography would effectively stratify patients with new symptoms in a cost-effective HF program aimed at early diagnosis of mild HF. A total of 252 patients were referred by 100 general practitioners.

RESULTS

Among the study population, the median BNP value was 78 ng/L (range, 5-1491 ng/L). BNP concentrations were lower among patients without heart disease [median 15 ng/L (range, 5-167 ng/L); n = 96] than among patients with confirmed HF [median, 165 ng/L (22-1491 ng/L); n = 157; Mann-Whitney U-test, 12.3; P <0.001]. Patients were grouped into diastolic dysfunction [BNP, 195 (223) ng/L], systolic dysfunction [BNP, 290 (394) ng/L], and both systolic and diastolic dysfunction [BNP, 776 (506) ng/L]. In this model, a cutoff value of 50 ng/L BNP increases the diagnostic accuracy in predicting mild HF, avoiding 41 echocardiograms per 100 patients studied, with a net saving of 14% of total costs.

CONCLUSIONS

Blood BNP concentrations, in a cost effective targeted screening, can play an important role in diagnosing mild HF and stratifying patients into risk groups of cardiac dysfunction.

Influence of atrial fibrillation on cardiac brain natriuretic peptide release during haemodynamic stress in heart failure

BACKGROUND

The determinants of release of brain natriuretic peptide (BNP) in heart failure (HF) are incompletely understood, particularly, the effect of heart rhythm and haemodynamic stress.

AIMS

To investigate the effect of haemodynamic stress on cardiac BNP release in HF and differentiate this response for atrial fibrillation (AF) and sinus rhythm (SR).

METHODS

In 18 HF patients (ejection fraction<40%, 9 in AF and 9 in SR) haemodynamics and BNP levels were measured from arterial and coronary sinus samples at baseline, after 10 min of 20 degrees passive head up tilt (HUT) and after 10 min of isometric handgrip (IHG) exercise. From these data, we calculated a transcardiac BNP gradient and compared results between the AF and SR cohort.

RESULTS

During haemodynamic stress in both groups, there were no significance differences in left sided filling pressures. At baseline, there were no differences in BNP measurements between the SR and AF group. The transcardiac BNP gradient increased significantly in the SR (p=0.02) but not the AF cohort, after HUT. During IHG exercise, there was a significant decrease in cardiac BNP release in the AF cohort (p=0.03) but not the SR cohort.

CONCLUSION

These data imply in HF, cardiac rhythm influences cardiac BNP release in response to haemodynamic stress.

Analytical evaluation of the Dade Behring Dimension RxL automated N-Terminal proBNP (NT-proBNP) method and comparison with the Roche Elecsys 2010

Methods to quantify B-type natriuretic peptide (BNP) and N-terminal-propeptide (NT-proBNP) in plasma or serum samples are well established. We assessed the analytical performance of the Dimension RxL NT-proBNP method (Dade-Behring). Evaluation of different sample types was carried out. Controls and heparin plasma pools were used to determine the detection limit, precision, and linearity. Sample stability and the effect of interfering substances on the NT-proBNP concentrations were evaluated. Agreement between Dimension RxL and Elecsys 2010 (Roche Diagnostics) NT-proBNP methods was assessed. The influence of age and sex on NT-proBNP concentrations was evaluated in healthy subjects. Heparin plasma should be the matrix of choice. The detection limit was 2.0ng/L. The total imprecision was 2.6–3.6% for concentrations from 231 to 9471ng/L; mean NT-proBNP concentrations of 21 and 15ng/L were associated with coefficients of variation of 9.9% and 14.7%, respectively. The method was linear up to 32,650ng/L. There was no effect of temperature, freeze-thaw cycles and interfering substances. A bias was detected when Dimension RxL and Elecsys 2010 NT-proBNP methods were compared. Age and sex were significantly and independently related to NT-proBNP concentrations. The Dimension RxL NT-proBNP method, like the Elecsys 2010, is suitable for routine use in the diagnosis of heart failure.