Diagnostic accuracy of pleural fluid NT-pro-BNP for pleural effusions of cardiac origin: a systematic review and meta-analysis

Pleural Effusions in Patients With Congestive Heart Failure: Frequency, Pathogenesis, Diagnosis, and Implications

Patients with cardiac disease frequently develop pleural effusions; the incidence is approximately 500,000 cases per year in the United States. These effusions often represent important clinical events for patients, indicating that either there has been an acute change in the patient's clinical status or the patient's chronic management program needs review. These effusions usually develop in both the right and left hemithorax but can be unilateral. The pathogenesis involves increased fluid transfer from parietal pleural capillaries into the pleural space and possibly decreased pleural fluid uptake into parietal pleural lymphatic structures. The increased fluid transfer develops due to increased capillary pressure secondary to elevated venous outflow pressure and secondary to decreased lymphatic flow into central vessels secondary to heart failure. Most pleural effusions associated with heart failure are transudates, but 20% to 25% have increased protein and lactate dehydrogenase levels suggesting an exudative process. Additional testing can clarify the situation and requires calculation of the serum albumin to pleural fluid albumin gradient or measurement of N-terminal pro-brain natriuretic peptide in the pleural fluid. An albumin gradient of greater than 1.2 g/dL suggests that the fluid is a transudate. The presence of a pleural effusion in a hospitalized patient at discharge is associated with an increased likelihood of rehospitalization and mortality within the next year. Patients with large symptomatic pleural effusions may require therapeutic thoracentesis. Recurrence of symptomatic effusions presents a management dilemma that might require repeated thoracenteses, indwelling intrapleural catheter placement, or other management steps used in advanced chronic heart failure.

Cardiac related pleural effusions: a narrative review

Background and Objective

Pleural effusions (PEs) are commonly seen in various pathologies and have a significant impact on patient health and quality of life. Unlike for malignant PEs, non-malignant PEs (NMPEs) do not have well-established guidelines. Much of the evidence base in this field is from a handful of randomised controlled trials (RCTs) and the majority are from retrospective cohort analyses and cases series. Cardiac related PEs fall within the entity of NMPEs and the aim of this narrative review is to gather the existing evidence in the field of congestive heart failure (CHF), pericarditis and post-cardiac injury syndrome (PCIS). This narrative review investigates the pathophysiology, diagnostic criteria and treatment options for the various cause of cardiac related PEs.

Methods

This narrative review is based on a comprehensive literature search analysing RCTs, prospective and retrospective cohort analyses and published case series.

Key Content and Findings

CHF related PEs have a substantial mortality rate and carry a worse prognosis if the PEs are bilateral and transudative in nature. Light's criteria have often shown to misclassify transudative effusions in CHF (pseudo-exudates) and hence measuring serum-pleural albumin gradient is an invaluable tool to accurately identify transudates. Elevated serum and pleural N-terminal pro-B type natriuretic peptide (NT-proBNP) has shown increasing evidence of correctly identifying PEs secondary to CHF. However, they should be considered with the pre-test probability of CHF. Therapeutic thoracentesis and indwelling pleural catheter (IPC) placement may be necessary if medical management has failed. PEs can also occur secondary to pericarditis and are often small, bilateral and exudative. PCIS also results in PEs and are commonly seen in post-coronary artery bypass graft (CABG) surgery. Both entities need management of the underlying cause first, but in cases where PEs are refractory, individualised pleural interventions may be necessary.

Conclusions

This comprehensive narrative review provides valuable insights into the aetiology, diagnosis and management of PEs secondary to CHF, pericarditis and PCIS. The aim is to enhance the clinicians' knowledge of this complex and controversial topic to improve patient care of cardiac-related PEs. Ongoing trials in this field will be able to provide valuable insights.

A Review of Current Practices and Future Trends in Body Fluid Testing

BACKGROUND

Body fluid testing in the clinical chemistry laboratory is a cornerstone in the diagnostic workup of pathological effusions. Laboratorians may not be aware of the preanalytical workflows used in the collection of body fluids though the value is evident whenever processes change or issues arise. The analytical validation requirements can vary depending on the regulations dictated by the laboratories' jurisdiction and accreditor requirements. Much of analytical validation hinges on how useful testing is to clinical care. Usefulness of testing varies with how well established and incorporated the tests and interpretation are in practice guidelines.

CONTENT

Body fluid collections are depicted and described so clinical laboratorians have a basic appreciation of what specimens are submitted to the laboratory for testing. A review of validation requirements by major laboratory accreditation entities is presented. A review of the usefulness and proposed decision limits for common body fluid chemistry analytes is presented. Body fluid tests that show promise and those that are losing (or lost long ago) value are also reviewed.

SUMMARY

The total testing process from collection to result interpretation can be complicated and easily overlooked by the clinical laboratory. This review aims to improve the understanding and awareness of collections, validation, result interpretation, and provide an update on recent trends.

A practical approach to pseudoexudative pleural effusions

Light's criteria falsely label a significant number of effusions as exudates. Such exudative effusions with transudative etiologies are referred to as "pseduoexudates". In this review, we discuss a practical approach to correctly classify an effusion that may be a pseudoexudate. A PubMed search yielded 1996 manuscripts between 1990 and 2022. Abstracts were screened and 29 relevant studies were included in this review article. Common etiologies for pseudoexudates include diuretic therapy, traumatic pleural taps, and coronary artery bypass grafting. Here, we explore alternative diagnostic criteria. Concordant exudates (CE), defined as effusions where proteins in pleural fluid/serum (PF/SPr) > 0.5 and pleural fluid LDH level of >160 IU/L (>2/3 upper limit of normal) confer higher predictive value to the Light's criteria. Serum-pleural effusion albumin gradient (SPAG) > 1.2 g/dL and serum-pleural effusion protein gradient (SPPG) > 3.1 g/dL together yielded a sensitivity of 100% in heart failure and a sensitivity of 99% in hepatic hydrothorax whe n identifying pseudoexudates (Bielsa et al., 2012) [5]. Pleural fluid N-Terminal Pro Brain Natriuretic Peptide (NTPBNP) offered a specificity and sensitivity of 99% in identifying pseudoexudates when using a cut-off of >1714 pg/mL (Han et al., 2008) [24]. However, its utility remains questionable. Additionally, we also looked at pleural fluid cholesterol and imaging modalities such as ultrasound and CT scan to measure pleural thickness and nodularity. Finally, the diagnostic algorithm we suggest involves using SPAG >1.2 g/dL and SPPG >3.1 g/dL in effusions classified as exudates when there is a strong clinical suspicion for pseudoexudates.

Optimal diagnostic strategies for pleural diseases and identifying high-risk patients

INTRODUCTION

Pleural diseases encompass a broad range of conditions with diverse and heterogenous etiologies. Diagnostics in pleural diseases thus represents a challenging field with a wide array of available testing to distinguish between the numerous causes of pleural disease. Nonetheless, deploying best practice diagnostics in this area is essential in reducing both duration o the investigation pathway and symptom burden.

AREAS COVERED

This article critically appraises the optimal diagnostic strategies and pathway in patients with pleural disease, reviewing the latest evidence and key practice points in achieving a treatable diagnosis in patients with pleural disease. We also cover future and novel directions that are likely to influence pleural diagnostics in the near future. PubMed was searched for articles related to pleural diagnostics (search terms below), with the date ranges including June 2012 to June 2022.

EXPERT OPINION

No single test will ever be sufficient to provide a diagnosis in pleural conditions. The key to reducing procedure burden and duration to diagnosis lies in personalizing the investigation pathway to patients and deploying tests with the highest diagnostic yield early (such as pleural biopsy in infection and malignancy). Novel biomarkers may also allow earlier diagnostic precision in the near future.

Pleural fluid biochemical analysis: the past, present and future

Identifying the cause of pleural effusion is challenging for pulmonologists. Imaging, biopsy, microbiology and biochemical analyses are routinely used for diagnosing pleural effusion. Among these diagnostic tools, biochemical analyses are promising because they have the advantages of low cost, minimal invasiveness, observer independence and short turn-around time. Here, we reviewed the past, present and future of pleural fluid biochemical analysis. We reviewed the history of Light’s criteria and its modifications and the current status of biomarkers for heart failure, malignant pleural effusion, tuberculosis pleural effusion and parapneumonic pleural effusion. In addition, we anticipate the future of pleural fluid biochemical analysis, including the utility of machine learning, molecular diagnosis and high-throughput technologies. Clinical Chemistry and Laboratory Medicine (CCLM) should address the topic of pleural fluid biochemical analysis in the future to promote specific knowledge in the laboratory professional community.

Biomarkers in Acute Heart Failure Syndromes: An Update

Heart failure is one of the leading healthcare problems in the world. Clinical data lacks sensitivity and specificity in the diagnosis of heart failure. Laboratory biomarkers are a non-invasive method of assessing suspected decompensated heart failure. Biomarkers such as natriuretic peptides have shown promising results in the management of heart failure. The literature does not provide comprehensive guidance in the utilization of biomarkers in the setting of acute heart failure syndrome. Many conditions that manifest with similar pathophysiology as acute heart failure syndrome may demonstrate positive biomarkers. The following is a review of biomarkers in heart failure, enlightening their role in diagnosis, prognosis and management of heart failure.

Evaluation of a new multiple regression model based on biochemical parameters for the distinction of canine exudates and transudates

BACKGROUND

The classification of effusions in human medicine currently uses biochemical parameters of verified analytical accuracy, while veterinary medicine is traditionally guided by protein content (TP) and total nucleated cell count (TNCC) in the effusion, without solid scientific support.

OBJECTIVE

We aimed to assess the accuracy of the current veterinary classification system to distinguish transudates from exudates and create new tools involving biochemical parameters that better classify canine cavitary effusions.

METHODS

Clinical, laboratory, and imaging data from 250 canine pleural and peritoneal effusions were retrospectively and prospectively collected, organized, and statistically evaluated. Multiple logistic regression analysis was performed using biochemical and cellular parameters.

RESULTS

For identifying exudates, the accuracy (87.7%, n = 204) of the best traditional classification system (TNCC > 3000 cells/μL) was similar to that of the individual biochemical cutoff values with the greatest accuracy in the abdominal cavity (eg, cholesterol, CHO-E > 40.1 mg/dL, 87.3%, n = 55). The accuracy of albumin (ALB-E > 0.8 g/dL) in the pleural cavity was nonetheless higher (100%, n = 23). The best multiple predictive models for any cavity used the percentage of neutrophils and CHO-E (n = 72), presenting an accuracy, sensitivity, and specificity for the diagnosis of exudate of 88%, 96%, and 67%, respectively.

CONCLUSIONS

Biochemical classification of pleural effusions has a higher accuracy than the traditional system (based on TP and TNCC). Utility and cutoff of analytes are different for each cavity. Implementing a multiple regression model or establishing ratios or gradients with concurrent serum values adds no significant improvement in the diagnostic potential of distinguishing transudate and exudates in dogs.

The Role of Deep Learning-Based Echocardiography in the Diagnosis and Evaluation of the Effects of Routine Anti-Heart-Failure Western Medicines in Elderly Patients with Acute Left Heart Failure

Objective

The role of deep learning-based echocardiography in the diagnosis and evaluation of the effects of routine anti-heart-failure Western medicines was investigated in elderly patients with acute left heart failure (ALHF).

Methods

A total of 80 elderly patients with ALHF admitted to Affiliated Hangzhou First People's Hospital from August 2017 to February 2019 were selected as the research objects, and they were divided randomly into a control group and an observation group, with 40 cases in each group. Then, a deep convolutional neural network (DCNN) algorithm model was established, and image preprocessing was carried out. The binarized threshold segmentation was used for denoising, and the image was for illumination processing to balance the overall brightness of the image and increase the usable data of the model, so as to reduce the interference of subsequent feature extraction. Finally, the detailed module of deep convolutional layer network algorithm was realized. Besides, the patients from the control group were given routine echocardiography, and the observation group underwent echocardiography based on deep learning algorithm. Moreover, the hospitalization status of patients from the two groups was observed and recorded, including mortality rate, rehospitalization rate, average length of hospitalization, and hospitalization expenses. The diagnostic accuracy of the two examination methods was compared, and the electrocardiogram (ECG) and echocardiographic parameters as well as patients' quality of life were recorded in both groups at the basic state and 5 months after drug treatment.

Results

After comparison, the rehospitalization rate and mortality rate of the observation group were lower than the rates of the control group, but the diagnostic accuracy was higher than that of the control group. However, the difference between the two groups of patients was not statistically marked (P > 0.05). The length and expenses of hospitalization of the observation group were both less than those of the control group. The specificity, sensitivity, and accuracy of the examination methods in the observation group were higher than those of the control group, and the differences were statistically marked (P < 0.05). There was a statistically great difference between the interventricular delay (IVD) of the echocardiographic parameters of patients from the two groups at the basic state and the left ventricular electromechanical delay (LVEMD) parameter values after 5 months of treatment (P < 0.05), but there was no significant difference in the other parameters. After treatment, the quality of life of patients from the two groups was improved, while the observation group was more marked than the control group (P < 0.05).

Conclusion

Echocardiography based on deep learning algorithm had high diagnostic accuracy and could reduce the possibility of cardiovascular events in patients with heart failure, so as to decrease the mortality rate and diagnosis and treatment costs. Moreover, it had an obvious diagnostic effect, which was conducive to the timely detection and treatment of clinical diseases.

Diagnostics in Pleural Disease

Pleural disease diagnostics represent a sprawling topic that has enjoyed a renaissance in recent years from humble beginnings. Whilst pleural patients are heterogeneous as a population and in the aetiology of the disease with which they present, we provide an overview of the typical diagnostic approach. Pleural fluid analysis is the cornerstone of the diagnostic pathway; however, it has many shortcomings. Strong cases have been made for more invasive upfront investigations, including image-guided biopsies or local anaesthetic thoracoscopy, in selected populations. Imaging can guide the diagnostic process as well as act as a vehicle to facilitate therapies, and this is never truer than with the recent advances in thoracic ultrasound.

GRADE guidelines: 21 part 2. Test accuracy: inconsistency, imprecision, publication bias, and other domains for rating the certainty of evidence and presenting it in evidence profiles and summary of findings tables

OBJECTIVES

This article provides updated GRADE guidance about how authors of systematic reviews and health technology assessments and guideline developers can rate the certainty of evidence (also known as quality of the evidence or confidence in the estimates) of a body of evidence addressing test accuracy (TA) on the domains imprecision, inconsistency, publication bias, and other domains. It also provides guidance for how to present synthesized information in evidence profiles and summary of findings tables.

STUDY DESIGN AND SETTING

We present guidance for rating certainty in TA in clinical and public health and review the presentation of results of a body of evidence regarding tests.

RESULTS

Supplemented by practical examples, we describe how raters of the evidence can apply the GRADE domains inconsistency, imprecision, and publication bias to a body of evidence of TA studies.

CONCLUSION

Using GRADE in Cochrane and other reviews as well as World Health Organization and other guidelines helped refining the GRADE approach for rating the certainty of a body of evidence from TA studies. Although several of the GRADE domains (e.g., imprecision and magnitude of the association) require further methodological research to help operationalize them, judgments need to be made on the basis of what is known so far.

Interpreting pleural fluid results

Interpreting pleural fluid results correctly requires an awareness of the possible aetiologies of a pleural effusion and an understanding of the reliability of the outcome of each investigation. All results must be interpreted within each different clinical context and knowledge of the pitfalls for each test is necessary when the diagnosis is unclear. This review aims to discuss the common aetiologies of a pleural effusion and some of the pitfalls in interpretation that can occur when the diagnosis is unclear.

Biomarkers for Pulmonary Vascular Remodeling in Systemic Sclerosis: A Pathophysiological Approach

Pulmonary arterial hypertension (PAH) is a severe complication of systemic sclerosis (SSc) associated with high morbidity and mortality. There are several biomarkers of SSc-PAH, reflecting endothelial physiology, inflammation, immune activation, extracellular matrix, metabolic changes, or cardiac involvement. Biomarkers associated with diagnosis, disease severity and progression have been identified, however, very few have been tested in a prospective setting. Some antinuclear antibodies such as nucleosome antibodies (NUC), anti-centromere antibodies (CENP-A/B) and anti-U3-ribonucleoprotein (anti-U3-RNP) are associated with PAH while anti-U1-ribonucleoprotein (anti-U1-RNP) is associated with a reduced PAH risk. Anti-endothelin receptor and angiotensin-1 receptor antibodies might be good markers of SSc-PAH and progression of pulmonary vasculopathy. Regarding the markers reflecting immune activation and inflammation, there are many inconsistent results. CXCL-4 was associated with SSc progression including PAH and lung fibrosis. Growth differentiation factor (GDF)-15 was associated with PAH and mortality but is not specific for SSc. Among the metabolites, kynurenine was identified as diagnostic marker for PAH, however, its pathologic role in the disease is unclear. Endostatin, an angiostatic factor, was associated with heart failure and poor prognosis. Established heart related markers, such as N-terminal fragment of A-type natriuretic peptide/brain natriuretic peptide (NT-proANP, NT-proBNP) or troponin I/T are elevated in SSc-PAH but are not specific for the right ventricle and may be increased to the same extent in left heart disease. Taken together, there is no universal specific biomarker for SSc-PAH, however, there is a pattern of markers that is strongly associated with a risk of vascular complications in SSc patients. Further comprehensive, multicenter and prospective studies are warranted to develop reliable algorithms for detection and prognosis of SSc-PAH.

Biochemical Analysis of Pleural Fluid and Ascites

Biochemical testing of peritoneal and pleural fluids is carried out widely, although the range of tests likely to be useful is limited in comparison to the repertoire of tests available in a modern biochemistry laboratory. Fluids accumulate when pathological processes cause an imbalance between hydrostatic pressure gradients, capillary membrane permeability and lymphatic capacity, resulting in protein-poor transudates or inflammatory exudates. In peritoneal fluid, albumin is the most useful test, for the calculation of the serum-ascites albumin gradient; protein and LDH have a role regarding risk and diagnosis of spontaneous bacterial peritonitis and amylase may be useful in diagnosing fluid accumulation due to pancreatitis. Peritoneal fluid pH and glucose are not indicated analyses. For pleural fluid, protein and LDH are important in distinguishing between transudate and exudate using Light's criteria; albumin and the serum-effusion albumin gradient may have a complementary role in patients already on diuretics. Pleural fluid pH is the most useful marker of infection although LDH and glucose are also used. Pleural fluid amylase is often measured but, if raised, is more likely to reflect a malignant process than pancreatic disease as the former is much more prevalent. Tumour markers in both peritoneal and pleural fluids generally have limited diagnostic accuracy for detecting local malignancy. Limited studies validating standard serum test methods for use with pleural and peritoneal fluids have been published but work is progressing in this area both in Australasia and overseas and opportunities exist for contributing to this effort.

Unilateral Pleural Effusions with More Than One Apparent Etiology. A Prospective Observational Study

RATIONALE

Evaluation of a pleural effusion has historically focused on establishing a single etiology. Pleural fluid may accumulate through multiple pathophysiological processes. The prevalence of multiple causes for pleural effusions has not been established. The identification of contributing processes may improve clinical outcomes.

OBJECTIVES

The objective of this prospectively collected case series was to establish the prevalence and nature of multiple etiologies for a unilateral pleural effusion.

METHODS

Consecutive patients presenting with an undiagnosed unilateral pleural effusion were recruited at a tertiary pleural center. Patients underwent a comprehensive structured diagnostic clinical evaluation and were followed up for a minimum of 12 months, after which one or more diagnoses were recorded independently by two experienced clinicians.

MEASUREMENTS AND MAIN RESULTS

One hundred thirty patients were recruited to the study over a 24-month period, and 126 patients completed follow up. Altogether, 88 patients (70%) had a single cause for their pleural effusion, and 38 (30%) had multiple causes. Serum N-terminal pro-brain natriuretic peptide (NT-pro BNP) greater than or equal to 1,500 pg/ml was predictive of multiple etiologies. NT-pro BNP had a sensitivity and specificity of 79 and 88%, respectively, for establishing heart failure as a primary or contributory cause. Thirteen patients with a malignant pleural effusion also had an NT-pro BNP greater than or equal to 1,500 pg/ml.

CONCLUSIONS

This study is the first to estimate the prevalence of more than one identifiable cause for a unilateral pleural effusion. Out of 130 study subjects, 38 (30%) had multiple causes for an effusion. The identification of multiple pathologies underlying an accumulation of fluid in the pleural space may be important in determining optimum treatment and improving patients' symptoms.

Systematic review and meta-analysis of vascular endothelial growth factor as a biomarker for malignant pleural effusions

Conventional methods may fail to identify the cause of pleural effusion (PE), thus establishing reliable biomarkers is deemed necessary. This study aimed at examining the role of vascular endothelial growth factor (VEGF) as a biomarker in the differentiation between malignant and benign PEs in adults. A comprehensive literature search in PubMed (Medline), Scopus (ELSEVIER), and Cochrane Central Register of Controlled Trials (CENTRAL) databases was conducted using keywords. We included studies that evaluated pleural and/or serum levels of VEGF among patients presenting with undiagnosed PE and the association between these levels and the final diagnosis. We performed a meta‐analysis to calculate the summary effect using the random effects model. Statistical analysis was performed with the statistical package for meta‐analysis Comprehensive Meta‐Analysis. Twenty studies were included in the systematic review, while 11 of them in the meta‐analysis. Pleural fluid VEGF levels among patients with malignant PE were increased by 1.93 ng/mL as compared to patients with benign PE (95% CI: 1.32–2.54, Q = 173, df (Q): 10, I² = 94.2%, P < 0.05). Serum VEGF levels among patients with malignant PE were increased respectively by 1.90 ng/mL (95% CI: 0.93–2.88, Q = 182, df (Q): 6, I² = 96.7%, P < 0.05). This study showed that malignant PEs were associated with higher levels of both pleural fluid and serum VEGF. VEGF appears to represent a promising biomarker for the differential diagnosis between benign and malignant PEs.

Cardiac biomarkers in cats

Cardiac biomarkers have been used in cats as part of the clinical assessment of heart disease for over a decade. They are widely available to practitioners through commercial reference laboratories. The evidence base for the use of cardiac biomarkers (primarily N-terminal pro-B type natriuretic peptide and cardiac troponin I) in cats is comprehensively reviewed in this article, focusing on each of six specific areas: distinguishing cardiac from non-cardiac causes of respiratory distress; measurement of cardiac biomarkers in urine and pleural fluid; identification of occult cardiomyopathy; effects of systemic disease on circulating concentrations of cardiac biomarkers; point-of-care biomarker testing, and the possible prognostic utility of cardiac biomarker measurement.

Differentiation of Cardiac from Noncardiac Pleural Effusions in Cats using Second-Generation Quantitative and Point-of-Care NT-proBNP Measurements

Background

Pleural effusion is a common cause of dyspnea in cats. N‐terminal pro‐B‐type natriuretic peptide (NT‐proBNP) measurement, using a first‐generation quantitative ELISA, in plasma and pleural fluid differentiates cardiac from noncardiac causes of pleural effusion.

Hypothesis/Objectives

To determine whether NT‐proBNP measurements using second‐generation quantitative ELISA and point‐of‐care (POC) tests in plasma and pleural fluid distinguish cardiac from noncardiac pleural effusions and how results compare to the first‐generation ELISA.

Animals

Thirty‐eight cats (US cohort) and 40 cats (UK cohort) presenting with cardiogenic or noncardiogenic pleural effusion.

Methods

Prospective cohort study. Twenty‐one and 17 cats in the US cohort, and 22 and 18 cats in the UK cohort were classified as having cardiac or noncardiac pleural effusion, respectively. NT‐proBNP concentrations in paired plasma and pleural fluid samples were measured using second‐generation ELISA and POC assays.

Results

The second‐generation ELISA differentiated cardiac from noncardiac pleural effusion with good diagnostic accuracy (plasma: sensitivity, 95.2%, specificity, 82.4%; pleural fluid: sensitivity, 100%, specificity, 76.5%). NT‐proBNP concentrations were greater in pleural fluid (719 pmol/L (134–1500)) than plasma (678 pmol/L (61–1500), P = 0.003), resulting in different cut‐off values depending on the sample type. The POC test had good sensitivity (95.2%) and specificity (87.5%) when using plasma samples. In pleural fluid samples, the POC test had good sensitivity (100%) but low specificity (64.7%). Diagnostic accuracy was similar between first‐ and second‐generation ELISA assays.

Conclusions and clinical importance

Measurement of NT‐proBNP using a quantitative ELISA in plasma and pleural fluid or POC test in plasma, but not pleural fluid, distinguishes cardiac from noncardiac causes of pleural effusion in cats.

Diagnostic Accuracy of Natriuretic Peptides for Heart Failure in Patients with Pleural Effusion: A Systematic Review and Updated Meta-Analysis

Background

Previous studies have reported that natriuretic peptides in the blood and pleural fluid (PF) are effective diagnostic markers for heart failure (HF). These natriuretic peptides include N-terminal pro-brain natriuretic peptide (NT-proBNP), brain natriuretic peptide (BNP), and midregion pro-atrial natriuretic peptide (MR-proANP). This systematic review and meta-analysis evaluates the diagnostic accuracy of blood and PF natriuretic peptides for HF in patients with pleural effusion.

Methods

PubMed and EMBASE databases were searched to identify articles published in English that investigated the diagnostic accuracy of BNP, NT-proBNP, and MR-proANP for HF. The last search was performed on 9 October 2014. The quality of the eligible studies was assessed using the revised Quality Assessment of Diagnostic Accuracy Studies tool. The diagnostic performance characteristics (sensitivity, specificity, and other measures of accuracy) were pooled and examined using a bivariate model.

Results

In total, 14 studies were included in the meta-analysis, including 12 studies reporting the diagnostic accuracy of PF NT-proBNP and 4 studies evaluating blood NT-proBNP. The summary estimates of PF NT-proBNP for HF had a diagnostic sensitivity of 0.94 (95% confidence interval [CI]: 0.90–0.96), specificity of 0.91 (95% CI: 0.86–0.95), positive likelihood ratio of 10.9 (95% CI: 6.4–18.6), negative likelihood ratio of 0.07 (95% CI: 0.04–0.12), and diagnostic odds ratio of 157 (95% CI: 57–430). The overall sensitivity of blood NT-proBNP for diagnosis of HF was 0.92 (95% CI: 0.86–0.95), with a specificity of 0.88 (95% CI: 0.77–0.94), positive likelihood ratio of 7.8 (95% CI: 3.7–16.3), negative likelihood ratio of 0.10 (95% CI: 0.06–0.16), and diagnostic odds ratio of 81 (95% CI: 27–241). The diagnostic accuracy of PF MR-proANP and blood and PF BNP was not analyzed due to the small number of related studies.

Conclusions

BNP, NT-proBNP, and MR-proANP, either in blood or PF, are effective tools for diagnosis of HF. Additional studies are needed to rigorously evaluate the diagnostic accuracy of PF and blood MR-proANP and BNP for the diagnosis of HF.

A wild bootstrap approach for the selection of biomarkers in early diagnostic trials

BACKGROUND

In early diagnostic trials, particularly in biomarker studies, the aim is often to select diagnostic tests among several methods. In case of metric, discrete, or even ordered categorical data, the area under the receiver operating characteristic (ROC) curve (denoted by AUC) is an appropriate overall accuracy measure for the selection, because the AUC is independent of cut-off points.

METHODS

For selection of biomarkers the individual AUC's are compared with a pre-defined threshold. To keep the overall coverage probability or the multiple type-I error rate, simultaneous confidence intervals and multiple contrast tests are considered. We propose a purely nonparametric approach for the estimation of the AUC's with the corresponding confidence intervals and statistical tests. This approach uses the correlation among the statistics to account for multiplicity. For small sample sizes, a Wild-Bootstrap approach is presented. It is shown that the corresponding intervals and tests are asymptotically exact.

RESULTS

Extensive simulation studies indicate that the derived Wild-Bootstrap approach keeps and exploits the nominal type-I error at best, even for high accuracies and in case of small samples sizes. The strength of the correlation, the type of covariance structure, a skewed distribution, and also a moderate imbalanced case-control ratio do not have any impact on the behavior of the approach. A real data set illustrates the application of the proposed methods.

CONCLUSION

We recommend the new Wild Bootstrap approach for the selection of biomarkers in early diagnostic trials, especially for high accuracies and small samples sizes.

Relationship Between Prohormone Brain Natriuretic Peptide (NT-proBNP) Level and Severity of Pulmonary Dysfunction in Patients With Chronic Congestive Heart Failure

Introduction: Congestive heart failure (CHF) is a common disease and its prevalence is increasing in industrialized countries. NT-proBNP measurement is an established diagnostic test for diagnosis of CHF in patients who present to emergency room with acute dyspnea. The primary object of this study was to determine the relationship between levels of brain natriuretic peptide precursor and severity of lung function impairment in patients with chronic CHF.

Methods: This cross-sectional and analytical study that performed in Tuberculosis and Lung Disease Research Center of Tabriz University of Medical Sciences on 95 patients with chronic heart failure, and relation between NT-proBNP levels and pulmonary function parameters were examined.

Results: Sixty-four patients were male and 31 were female. The average age of male and females was 62.90 ± 11.54 and 61.61 ± 11.98 years, respectively. A significant inverse linear correlation was found between NT-proBNP and FEV1 (P < 0.001, r = -0.367), FVC (P < 0.001, r = -0.444), TLC (P = 0.022, r = -0.238), maximal midexpiratory flow (MMEF) (P = 0.047, r = -0.207) and left ventricular ejection fraction (LVEF) (P < 0.001, r = -0.461). A significant positive linear correlation was found between NT-proBNP and FEV1/FVC (P = 0.013, r = 0.257), RV/TLC (P = 0.003, r=0.303) and 5 Hz Raw (r = 0.231, P = 0.024).

Conclusion: This study showed that, both restrictive and obstructive ventilator impairments can occur in chronic CHF and as NT-proBNP increases appropriate to hemodynamic deterioration, pulmonary dysfunction increases.

Cautious application of pleural N-terminal pro-B-type natriuretic peptide in diagnosis of congestive heart failure pleural effusions among critically ill patients

Background and Objective

Several studies on diagnostic accuracy of pleural N-terminal pro-B-type natriuretic peptide (NT-pro-BNP) for effusions from congestive heart failure (CHF) conclude that pleural NT-pro-BNP is a useful biomarker with high diagnostic accuracy for distinguishing CHF effusions. However, its applicability in critical care settings remains uncertain and requires further investigations.

Methods

NT-proBNP was measured in pleural fluid samples of a prospective cohort of intensive care unit patients with pleural effusions. Receiver operating characteristic curve analysis was performed to determine diagnostic accuracy of pleural NT-proBNP for prediction of CHF effusions.

Results

One hundred forty-seven critically ill patients were evaluated, 38 (26%) with CHF effusions and 109 (74%) with non-CHF effusions of various causes. Pleural NT-proBNP levels were significantly elevated in patients with CHF effusions. Pleural NT-pro-BNP demonstrated the area under the curve of 0.87 for diagnosing effusions due to CHF. With a cutoff of 2200 pg/mL, pleural NT-proBNP displayed high sensitivity (89%) but moderate specificity (73%). Notably, 29 (27%) of 109 patients with non-CHF effusions had pleural NT-proBNP levels >2200 pg/mL and these patients were more likely to experience septic shock (18/29 vs. 10/80, P<0.001) or acute kidney injury (19/29 vs. 9/80, P<0.001).

Conclusions

Among critically ill patients, pleural NT-proBNP measurements remain a useful diagnostic aid in evaluation of pleural effusions. However, patients with non-CHF effusions may exhibit high pleural NT-proBNP concentrations if they suffer from septic shock or acute kidney injury. Accordingly, it is suggested that clinical context should be taken into account when interpreting pleural NT-proBNP values in critical care settings.

[Contribution of pleural fluid analysis to the diagnosis of pleural effusion]

Analysis of pleural fluid can have, on its own, a high diagnostic value. In addition to thoracocentesis, a diagnostic hypothesis based on medical history, physical examination, blood analysis and imaging tests, the diagnostic effectiveness will significantly increase in order to establish a definite or high probable diagnosis in a substantial number of patients. Differentiating transudates from exudates by the classical Light's criteria helps knowing the pathogenic mechanism resulting in pleural effusion, and it is also useful for differential diagnosis purposes. An increased N-terminal pro-brain natriuretic peptide, both in the fluid and in blood, in a due clinical context, is highly suggestive of heart failure. The presence of an increased inflammatory marker, such as C-reactive protein, together with the presence of over 50% of neutrophils is highly suggestive of parapneumonic pleural effusion. If, in these cases, the pH is<7.20, then the likelihood of complicated pleural effusion is high. There remains to be demonstrated the usefulness of other markers to differentiate complicated from uncomplicated effusions. An adenosine deaminase > 45 U/L and>50% lymphocytes is suggestive of tuberculosis. If a malignant effusion is suspected but the cytological result is negative, increased concentrations of some markers in the pleural fluid can yield high specificity values. Increased levels of mesothelin and fibruline-3 are suggestive of mesothelioma. Immunohistochemical studies can be useful to differentiate reactive mesothelial cells, mesothelioma and metastatic adenocarcinoma. An inadequate use of the information provided by the analysis of pleural fluid would results in a high rate of undiagnosed effusions, which is unacceptable in current clinical practice.

Diagnostic tools of pleural effusion

Pleural effusion is not a rare disease in Korea. The diagnosis of pleural effusion is very difficult, even though the patients often complain of typical symptoms indicating of pleural diseases. Pleural effusion is characterized by the pleural cavity filled with transudative or exudative pleural fluids, and it is developed by various etiologies. The presence of pleural effusion can be confirmed by radiological studies including simple chest radiography, ultrasonography, or computed tomography. Identifying the causes of pleural effusions by pleural fluid analysis is essential for proper treatments. This review article provides information on the diagnostic approaches of pleural effusions and further suggested ways to confirm their various etiologies, by using the most recent journals for references.

Identifying transudates misclassified by Light's criteria

PURPOSE OF REVIEW

Light's criteria combine three dichotomous tests into a decision rule that is considered positive if any one of the tests is positive. This strategy clearly maximizes sensitivity, although at the expense of specificity. Although Light's criteria identify 98% of pleural exudates, they misclassify about 25% of transudates as exudates. The way to overcome this limitation is discussed in this review.

RECENT FINDINGS

Traditionally, measurement of the protein gradient between the serum and pleural fluid has been recommended to decrease the misclassification rate of Light's criteria. A recent study demonstrated that a gradient between the albumin levels in the serum and the pleural fluid more than 1.2 g/dl performs significantly better than a protein gradient more than 3.1 g/dl to correctly categorize mislabeled cardiac effusions (83 vs. 55%). On the other hand, the accuracy of a pleural fluid to serum albumin ratio less than 0.6 excelled when compared with albumin and protein gradients in patients with miscategorized hepatic hydrothoraces (77 vs. 62 vs. 61%).

SUMMARY

The simplest strategy to reveal the true transudative nature of heart failure-related effusions, labeled as exudates by Light's criteria, is to calculate the serum to pleural fluid albumin gradient. Conversely, for misclassified hepatic hydrothoraces, measurement of the pleural to serum albumin ratio is recommended. The serum to pleural fluid protein gradient should no longer be considered the preferred test for this purpose.

Differentiating between feline pleural effusions of cardiac and non-cardiac origin using pleural fluid NT-proBNP concentrations

OBJECTIVE

To assess whether pleural fluid and urine amino terminal proB-type natriuretic peptide (NT-proBNP) can distinguish cardiac from non-cardiac causes of pleural effusion.

METHODS

Blood, urine and pleural fluid were prospectively collected from cats presenting with pleural effusion categorised as cardiac or non-cardiac in origin. NT-ProBNP concentrations were measured using a feline-specific enzyme-linked immunosorbent assay. Groups were statistically compared and receiver operating characteristic curves constructed to determine cut-offs to distinguish cardiac from non-cardiac pleural effusion in plasma, pleural fluid and urine.

RESULTS

Forty cats with pleural effusion (22 cardiac and 18 non-cardiac) were studied. NT-proBNP concentrations in plasma and pleural fluid were strongly correlated. Plasma (P<0·001) and pleural fluid (P<0·001) NT-proBNP concentrations and urinary NT-proBNT/creatinine ratios (P=0·035) were significantly higher in the cardiac group. After receiver operating characteristic curve analysis a plasma NT-proBNP cut-off of 214·3 pmol/mL was suggested [sensitivity=86·4% (95% CI: 66·7 to 95·3%), specificity=88·9% (95% CI: 67·2 to 96·9%)] and a pleural fluid NT-proBNP cut-off of 322·3 pmol/mL was suggested [sensitivity=100% (95% CI: 85·1 to 100%), specificity=94·4% (95% CI: 74·2 to 99·0%)]. No cut-off with adequate sensitivity and specificity for urinary NT-proBNP/creatinine ratios was suggested.

CLINICAL SIGNIFICANCE

Measurement of NT-proBNP in pleural fluid distinguishes cardiac from non-cardiac causes of pleural effusion in cats.

Comparison of pleural N-terminal pro-B-type natriuretic peptide, midregion pro-atrial natriuretic peptide and mid-region pro-adrenomedullin for the diagnosis of pleural effusions associated with cardiac failure

BACKGROUND AND OBJECTIVE

The purpose of this study was to compare the diagnostic utility of pleural fluid N-terminal pro-B-type natriuretic peptide (NT-proBNP), midregion pro-atrial natriuretic peptide (MR-proANP) and midregion pro-adrenomedullin (MR-proADM) for discriminating heart failure (HF)-associated effusions.

METHODS

NT-proBNP, MR-proANP and MR-proADM were measured by commercially available methodologies in the pleural fluid of a retrospective cohort of 185 consecutive patients with pleural effusions, of whom 95 had acute decompensated HF. Receiver-operating characteristic and area under the curve (AUC) analyses allowed comparisons of the discriminative properties of these biomarkers to be made at their optimal cut-off points.

RESULTS

The diagnostic accuracy of NT-proBNP and MR-proANP for HF as quantified by the AUC was 0.935 and 0.918, respectively, whereas MR-proADM was of limited value (AUC = 0.62). A pleural fluid MR-proANP >260 pmol/L or NT-proBNP >1700 pg/mL argues for HF (likelihood ratio (LR) positive >5), while levels below these cut-off values significantly decrease the probability of having the disease (respective LR negative 0.19 and 0.10). The optimal cut-off points for natriuretic peptides were influenced by age, renal function and body mass index. Finally, both NT-proBNP and the albumin gradient correctly identified more than 80% of those cardiac effusions misclassified as exudates by standard criteria.

CONCLUSIONS

MR-proANP is as valuable a diagnostic tool as NT-proBNP for diagnosing or excluding HF as the cause of pleural effusion.

Anatomy and pathophysiology of the pleura and pleural space

Pleural effusions are most often secondary to an underlying condition and may be the first sign of the underlying pathologic condition. The balance between the hydrostatic and oncotic forces dictates pleural fluid homeostasis. The parietal pleura has a more significant role in pleural fluid homeostasis. Its vessels are closer to the pleural space compared with its visceral counterpart; it contains lymphatic stomata, absent on visceral pleura, which are responsible for a bulk clearance of fluid. The diagnosis and successful treatment of pleural effusions requires a mixture of imaging techniques and pleural fluid analysis.

The Light criteria: the beginning and why they are useful 40 years later

The Light criteria serve as a good starting point in the separation of transudates from exudates. The Light criteria misclassify about 25% of transudates as exudates, and most of these patients are on diuretics. If a patient is thought likely to have a disease that produces a transudative pleural effusion but the Light criteria suggest an exudate by only a small margin, the serum-pleural fluid protein gradient should be examined.

Pleural fluid biomarkers: beyond the Light criteria

Although distinguishing transudates from exudates through the Light criteria is still considered a pragmatic first step in the diagnostic work-up of pleural effusions, the measurement of various pleural fluid biomarkers may aid in the identification of common and specific entities, such as heart failure (natriuretic peptides), tuberculosis (adenosine deaminase), malignancy (mesothelin, fibulin-3, immunocytochemical stains), or bacterial pleural infections (C-reactive protein). The use of these biomarkers is currently encouraged as a routine diagnostic procedure.

Pleural fluid analysis: standstill or a work in progress?

Pleural fluid analysis yields important diagnostic information in pleural effusions in combination with clinical history, examination, and radiology. For more than 30 years, the initial and most pragmatic step in this process is to determine whether the fluid is a transudate or an exudate. Light's criteria remain the most robust in separating the transudate-exudate classification which dictates further investigations or management. Recent studies have led to the evaluation and implementation of a number of additional fluid analyses that may improve the diagnostic utility of this method. This paper discusses the current practice and future direction of pleural fluid analysis in determining the aetiology of a pleural effusion. While this has been performed for a few decades, a number of other pleural characteristics are becoming available suggesting that this diagnostic tool is indeed a work in progress.

Natriuretic peptides: Diagnostic and therapeutic use

Natriuretic peptides (NPs) are hormones which are mainly secreted from heart and have important natriuretic and kaliuretic properties. There are four different groups NPs identified till date [atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), C-type natriuretic peptide (CNP) and dendroaspis natriuretic peptide, a D-type natriuretic peptide (DNP)], each with its own characteristic functions. The N-terminal part of the prohormone of BNP, NT-proBNP, is secreted alongside BNP and has been documented to have important diagnostic value in heart failure. NPs or their fragments have been subjected to scientific observation for their diagnostic value and this has yielded important epidemiological data for interpretation. However, little progress has been made in harnessing the therapeutic potential of these cardiac hormones.

Utilization of B-type natriuretic peptide and NT-proBNP in the diagnosis of pleural effusions due to heart failure

PURPOSE OF REVIEW

The natriuretic peptides B-type natriuretic peptide (BNP) and NT-proBNP have been incorporated into the existing clinical guidelines for the diagnostic evaluation of heart failure. Recent evidence has provided important information regarding the relative value of each of these peptides to differentiate between pleural effusions caused by heart failure and those attributable to other causes.

RECENT FINDINGS

In a meta-analysis of 10 studies, which included 1120 patients, pleural fluid levels of NT-proBNP had a pooled sensitivity and specificity of 94%, a positive likelihood ratio of 15.2, and a negative likelihood ratio of 0.06 in identifying heart failure-related effusions. Because pleural fluid and serum natriuretic peptide levels are closely correlated and display similar discriminatory properties, blood tests alone are sufficient. More than 85% of heart failure patients whose pleural fluids meet exudative criteria exhibit high pleural NT-proBNP concentrations. The diagnostic performance of pleural fluid BNP has been reported to be inferior to that of NT-proBNP.

SUMMARY

NT-proBNP is an established biomarker of heart failure-associated effusions and the most effective tool for recognizing cardiac effusions that are misclassified as exudates by Light's criteria. If clinicians choose pleural fluid specimens for natriuretic peptide testing, the lower diagnostic accuracy of BNP makes it a poor substitute for NT-proBNP measurements.