A meta-analysis derivation of continuous likelihood ratios for diagnosing pleural fluid exudates

Meigs Syndrome and Elevated CA-125: Case Report and Literature Review of an Unusual Presentation Mimicking Ovarian Cancer

Background and Objectives: Meigs syndrome is represented by a benign adnexal tumor, ascites, and hydrothorax. Even though the ovarian mass is often characterized by a fibroma-like origin, cancer antigen-125 (CA-125) serum levels could be elevated as in the development of ovarian cancer. Here, we present the case of a patient with Meigs syndrome and increased CA-125. Materials and Methods: We performed systematic research for articles including similar cases in PubMed, EMBASE, and Scopus in February 2023, adopting the string of idioms: "Meigs syndrome AND Cancer antigen 125", and following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Results: Eligible records were 25. Hydrothorax was right-sided in 10 cases over 25; left-sided in two patients over 25. Concerning ascites, two patients showed more than 6 L of ascitic fluid, whereas three patients had 6 L or less. CA-125 elevation ranged from 149 IU/mL to 3803 IU/mL. Adnexal mass histotypes were: struma ovarii (12 cases), thecomas (two cases), fibrothecomas (five cases), fibromas (five cases), and one sclerosing stromal tumor (SST). Conclusions: In postmenopausal women with elevated CA-125 serum levels and an adnexal mass suspicious for malignancy at ultrasound (US), ascites and pleural effusion, surgery, and histopathological examination are necessary. MS is a diagnostic option, with an excellent prognosis after exeresis of the mass.

The laboratory investigation of pleural fluids: An update based on the available evidence

Selecting appropriate laboratory tests based on available evidence is central to improve clinical effectiveness and impacting on patient outcome. Although long studied, there is no mutual agreement upon pleural fluid (PF) management in the laboratory context. Given the experienced confusion about the real contribution of laboratory investigations to guide clinical interpretation, in this update, we tried to identify useful tests for the PF analysis, aiming to unravel critical points and to define a common line in requesting modalities and practical management. We performed a careful literature review and a deepened study on available guidelines to finalize an evidence-based test selection, intended for clinicians' use to streamline PF management. The following tests depicted the basic PF profile routinely needed: (1) abbreviated Light's criteria (PF/serum total protein ratio and PF/serum lactate dehydrogenase ratio) and (2) cell count with differential analysis of haematological cells. This profile fulfils the primary goal to determine the PF nature and discriminate between exudative and transudative effusions. In specific circumstances, clinicians may consider additional tests as follows: the albumin serum to PF gradient, which reduces exudate misclassification rate by Light's criteria in patients with cardiac failure assuming diuretics; PF triglycerides, in differentiating chylothorax from pseudochylothorax; PF glucose, for identification of parapneumonic effusions and other causes of effusion, such as rheumatoid arthritis and malignancy; PF pH, in suspected infectious pleuritis and to give indications for pleural drainage; and PF adenosine deaminase, for a rapid detection of tuberculous effusion.

Pleural effusion in critically ill patients and intensive care setting

Pleural effusion usually causes a diagnostic dilemma with a long list of differential diagnoses. Many studies found a high prevalence of pleural effusions in critically ill and mechanically ventilated patients, with a wide range of variable prevalence rates of up to 50%-60% in some studies. This review emphasizes the importance of pleural effusion diagnosis and management in patients admitted to the intensive care unit (ICU). The original disease that caused pleural effusion can be the exact cause of ICU admission. There is an impairment in the pleural fluid turnover and cycling in critically ill and mechanically ventilated patients. There are also many difficulties in diagnosing pleural effusion in the ICU, including clinical, radiological, and even laboratory difficulties. These difficulties are due to unusual presentation, inability to undergo some diagnostic procedures, and heterogenous results of some of the performed tests. Pleural effusion can affect the patient’s outcome and prognosis due to the hemodynamics and lung mechanics changes in these patients, who usually have frequent comorbidities. Similarly, pleural effusion drainage can modify the ICU-admitted patient’s outcome. Finally, pleural effusion analysis can change the original diagnosis in some cases and redirect the management toward a different way.

Non-invasive characterization of pleural and pericardial effusions using T1 mapping by magnetic resonance imaging

AIMS

Differentiating exudative from transudative effusions is clinically important and is currently performed via biochemical analysis of invasively obtained samples using Light's criteria. Diagnostic performance is however limited. Biochemical composition can be measured with T1 mapping using cardiovascular magnetic resonance (CMR) and hence may offer diagnostic utility for assessment of effusions.

METHODS AND RESULTS

A phantom consisting of serially diluted human albumin solutions (25-200 g/L) was constructed and scanned at 1.5 T to derive the relationship between fluid T1 values and fluid albumin concentration. Native T1 values of pleural and pericardial effusions from 86 patients undergoing clinical CMR studies retrospectively analysed at four tertiary centres. Effusions were classified using Light's criteria where biochemical data was available (n = 55) or clinically in decompensated heart failure patients with presumed transudative effusions (n = 31). Fluid T1 and protein values were inversely correlated both in the phantom (r = -0.992) and clinical samples (r = -0.663, P < 0.0001). T1 values were lower in exudative compared to transudative pleural (3252 ± 207 ms vs. 3596 ± 213 ms, P < 0.0001) and pericardial (2749 ± 373 ms vs. 3337 ± 245 ms, P < 0.0001) effusions. The diagnostic accuracy of T1 mapping for detecting transudates was very good for pleural and excellent for pericardial effusions, respectively [area under the curve 0.88, (95% CI 0.764-0.996), P = 0.001, 79% sensitivity, 89% specificity, and 0.93, (95% CI 0.855-1.000), P < 0.0001, 95% sensitivity; 81% specificity].

CONCLUSION

Native T1 values of effusions measured using CMR correlate well with protein concentrations and may be helpful for discriminating between transudates and exudates. This may help focus the requirement for invasive diagnostic sampling, avoiding unnecessary intervention in patients with unequivocal transudative effusions.

Pleural Fluid Analysis: Are Light's Criteria Still Relevant After Half a Century?

Fifty years from their initial description, Light's criteria are still unhesitatingly accepted as the default reference test for separating pleural transudates and exudates. Efforts should be focused not so much on trying to find an even more reliable technique for categorizing PEs but on improving the misclassification rate of transudates that characterize Light's criteria. Despite their shortcomings, Light's criteria may well continue their reign for another 50 years. Long live the Light's criteria!

Efficacy of Ultrasonography in the Diagnosis of Transudative Pleural Fluids

AIMS

We aimed to evaluate the efficacy of thoracic ultrasonography (USG) in diagnosis of pleural exudates and transudates using pleural thickness (PT) measurement.

PATIENTS AND METHODS

Patients who underwent investigations for pleural fluid between January 2018 and May 2018 were included in this prospective study. The patients were evaluated using radiologic imaging modalities to detect pleural fluid, and PT was measured using thoracic USG. The patients were then divided into 2 groups according to Light's criteria as transudative pleural fluid (TPF) and exudative pleural fluid (EPF), and the results were compared between the groups.

RESULTS

A total of 73 patients were included in the study. The mean age was 62±15.1 years. Forty-eight patients (65.8%) had EPF and 25 (34.2%) had TPF. Thoracic USG revealed a mean PT of 0.3±0.1 cm in the TPF group and 0.6±0.3 cm in the EPF group (P<0.001). The optimal cut-off value for PT was 0.2 cm in the TPF group. The sensitivity and specificity of thoracic USG were calculated as 87.5% and 56%, respectively.

CONCLUSION

The measurement of PT using thoracic USG in this study has a high sensitivity but low specificity for identifying transudates from exudates. This approach may be useful in patients who refuse thoracentesis or have a contraindication for the procedure, and in emergency and intensive care unit settings. We recommend further studies to determine the efficacy of thoracic USG studies in patients with pleural fluids.

Diagnosis of Parapneumonia Pleural Effusion with Serum and Pleural Fluid Cell-Free DNA

Objective

As cell-free DNA levels in the pleural fluid and serum of parapneumonic pleural effusion (PPE) patients have not been thoroughly explored, we evaluated their diagnostic potential.

Methods

Twenty-two PPE and 16 non-PPE patients were evaluated. Serum and pleural fluids were collected, and cell-free DNA was quantified. All biomarkers were assessed for correlation with days after admission. Receiver operating characteristic (ROC) curve analysis was used to determine diagnostic accuracy and optimal cut-off point.

Results

Nuclear and mitochondrial DNA levels in the pleural fluid and nuclear DNA levels in serum of PPE patients were significantly higher than in those of the non-PPE patients. However, only cell-free DNA levels in pleural fluid correlated with days after admission among PPE patients (r= 0.464, 0.538, respectively). ROC curve analysis showed that nuclear and mitochondrial DNA in pleural fluid had AUCs of 0.945 and 0.889, respectively. With cut-off values of 134.9 and 17.8 ng/ml for nuclear and mitochondrial DNA in pleural fluid, respectively, 96% sensitivity and 81% specificity were observed for PPE diagnosis.

Conclusion

Nuclear and mitochondrial DNA in pleural fluid possess PPE diagnostic potential and correlated with disease severity. Serum nuclear DNA could also be used to distinguish freshly admitted PPE patients (Day 1) from non-PPE patients, but with less accuracy.

The use of light's criteria in hospitalized children with a pleural effusion of unknown etiology

OBJECTIVE

Pleural effusions are common in pediatrics. When the etiology of a pleural effusion remains unknown, adult literature recommends the use of Light's criteria to differentiate a transudate from an exudate. Pediatricians may rely on adult literature for the diagnostic management of pleural effusions as Light's criteria has not been validated in children. The purpose of this study was to review the use of Light's criteria in hospitalized children with a pleural effusion of unknown etiology.

METHODS

Retrospective review was performed on children hospitalized with a pleural effusion requiring chest tube placement or thoracentesis between January 1, 2016 to January 1, 2017 at Children's Hospital Colorado. Charts were reviewed for primary team, use of Light's criteria, pleural effusion diagnosis, and 30-day recurrence of repeat intervention or fluid analysis.

RESULTS

Sixty-eight patients were hospitalized with a pleural effusion of unknown etiology requiring intervention. Only 16 pleural effusions (24%) were classified using Light's criteria. In those patients for whom Light's criteria was used, a diagnosis or change in management occurred in 10 of 16 patients (63%). Pleural effusions were most common on the cardiology service (26/68). Use of Light's criteria was most frequent on the oncology service (7/8). Thirty-day need for repeat intervention was lower in those with Light's criteria (13%) compared to those without (27%).

CONCLUSIONS

Light's criteria were utilized infrequently in hospitalized children with a pleural effusion of unknown etiology at a single institution. There was considerable practice variation among provider teams. When utilized, Light's criteria assisted in making a diagnosis or changing management in many patients, and may lead to a reduction in 30-day recurrence requiring repeat intervention.

Concordant and Discordant Exudates and Their Effect on the Accuracy of Light's Criteria to Diagnose Exudative Pleural Effusions

INTRODUCTION

To describe the incidence of discordant exudate (DE) effusions, their underlying etiologies and their effect on the accuracy of the Light's criteria to diagnose exudate effusions.

METHODS

A retrospective review of pleural fluid analysis (PFA) from a cohort of patients with pleural effusion (PE) who underwent thoracentesis. PEs were defined as exudative based on the Light's criteria. The effusions were further classified in concordant or DE.

RESULTS

From 847 PE samples, 611 (72.1%) were diagnosed as an exudate and 236 (27.9%) as a transudate. In 10.3% of cases (n = 87), there was discordancy between the final pleural fluid diagnosis and the PFA defined by Light's criteria. 281 (33.2%) of the 632 effusions classified as an exudate by Light's criteria were DE (52 transudates and 229 exudates). 182 (65%) of the 281 DE were found to be protein discordant (37 transudates and 145 exudates), and 99 (35.2%) were lactate dehydrogenase discordant (15 transudates and 84 exudates). The positive predictive value and positive likelihood ratio of Light's criteria for the diagnosis of an exudate effusion decreased from 99.4% and 67.4%, respectively, when the exudates were concordant to 81.5% and 1.7, respectively, if they were discordant.

CONCLUSIONS

In a significant percentage of patients, there is discordancy between the results of the PFA and the final clinical diagnosis. DE decreased the accuracy of Light's criteria to identify exudate PE, increasing the risk of misclassifying a transudate as an exudate. Concordant exudates almost universally established the presence of an exudative PE.

Pleural Effusion in Meigs' Syndrome-Transudate or Exudate?: Systematic Review of the Literature

Although Meigs' syndrome is regarded as a well-defined entity, contradictory data on pleural fluid characteristics have been presented, with some papers classifying it as a transudate, whereas others stating that it is an exudate.The aims of the study were: (1) to evaluate pleural fluid characteristics in patients with Meigs' syndrome and (2) to analyze the prevalence of transudative and exudative pleural effusion in relation to the applied definition of the syndrome.We performed a search through medical databases (MEDLINE, EMBASE, SCOPUS, and GOOGLE SCHOLAR) to identify papers on Meigs' syndrome published between 1940 and 2013. Two authors independently reviewed each paper searching for prespecified data: (1) signs and symptoms, (2) tumor characteristics, (3) clinical and laboratory data on ascites, (4) clinical, radiological, and laboratory data on pleural fluid, (5) clinical course after tumor removal. All case reports were reclassified according to a new unequivocal classification of Meigs' syndrome-related entities.A total of 653 papers were initially identified, and 454 articles reporting 541 patients were included in the final analysis. After reclassification according to our case definitions, there were 196, 113, and 108 patients defined as classic Meigs' syndrome, nonclassic Meigs' syndrome, and pseudo-Meigs' syndrome, respectively. Significantly more patients presented with right-sided than left-sided and bilateral pleural effusions (P < 0.001). Median volume of withdrawn pleural fluid was 2950 (1500-6000) mL. The classification of pleural effusion with the use of Light's criteria was possible in only 7 patients. In 6 of these patients pleural effusion met the criteria for an exudate. When the protein concentration > 3.0 g/dL was applied as a criterion of pleural exudate, 88.8% (80/90) of effusions were classified as exudates. Increasing the cut-off level to 3.5 g/dL resulted in only a modest decrease in the percentage of exudative effusions (81%, 73/90).Surprisingly few reports on Meigs' syndrome present data reliably defining the character of pleural effusion. The available data indicate, however, that the majority of pleural effusions in patients with this entity are exudates. This finding may be a prerequisite for the verification of some earlier presented concepts.

Delayed onset of benign pleural effusion following concurrent chemoradiotherapy for inoperable non-small-cell lung cancer

Chronic benign pleural effusion (BPE) is a rare complication of concurrent chemoradiotherapy (CRT) for inoperable stage IIIA non-small-cell lung cancer (NSCLC). This report presents three cases of BPE, the workup to differentiate this benign condition from recurrence of cancer and recommends a pleural biopsy as part of the diagnostic process. These inflammatory exudates often remain indolent, and may not require drainage or surgical intervention. In the absence of clinical, radiological and pathological evidence of recurrent disease, we recommend clinicians manage these patients expectantly, using regular clinical assessment and imaging.

Improving the predictive accuracy of identifying exudative effusions

BACKGROUND

Application of Light's criteria results in misclassification of some transudative effusions as exudative, particularly because of congestive heart failure (CHF). We sought to determine if the serum to pleural fluid albumin (SF-A) and serum to pleural fluid protein (SF-P) gradients increased the predictive accuracy to correctly identify exudative effusions.

METHODS

We retrospectively analyzed 1,153 consecutive patients who underwent a diagnostic thoracentesis at the Medical University South Carolina. Univariable logistic regression analyses were used to determine the statistical significance of pleural fluid tests that correctly identified exudative effusions. Tests with significant diagnostic accuracy were combined in multivariable logistic regression models, with calculation of areas under the curve (AUCs) to determine their predictive accuracy. The predictive capability of the best model was compared with Light's criteria and other test combinations.

RESULTS

Pleural fluid lactate dehydrogenase (LDH), SF-A gradient, and SF-P gradient had a significant effect on the probability of identifying exudative pleural effusions. When combined together in a multivariable logistic regression, LDH (OR, 14.09 [95% CI, 2.25-85.50]), SF-A gradient (OR, 7.16 [95% CI, 1.24-41.43]), and SF-P gradient (OR, 6.83 [95% CI, 1.56-27.88]) had an AUC of 0.92 (95% CI, 0.85-0.98).

CONCLUSIONS

Application of Light's criteria, not uncommonly, misclassifies CHF transudative effusions as exudates. In cases where no cause for an exudative effusion can be identified or CHF is suspected, the sequential application of the fluid LDH, followed by the SF-P and then the SF-A gradients, may assist in reclassifying pleural effusions as transudates.

Pleural cholesterol to the diagnosis of exudative effusion

Introduction:

Diagnostic approaches to patients with a pleural effusion must be precise because many procedures depend on the nature of the fluid in the effusion. To date, no biochemical test is considered an appropriate alternative to Light’s criteria. This study compared the absolute pleural cholesterol (PC) level and the pleural cholesterol/serum cholesterol (PC/SC) ratio with Light’s criteria to determine exudative pleural effusions.

Materials and Methodology:

This study was a case series of 100 consecutive patients with pleural effusions. The clinical parameters that were used to diagnosis an exudative effusion included the cholesterol level, a pleural cholesterol level ≥ 50 mg/dL, a pleural/serum ratio ≥ 0.4, and Light’s criteria. The sensitivity, specificity, and positive and negative predictive values of each test for the diagnosis of an exudative effusion were assessed.

Results:

A total of 79 patients were definitively diagnosed with an exudative effusion and were included in the trial and analyzed. The mean PC level in the exudates was 90.39 mg/dL. The PC levels demonstrated a sensitivity of 97.22%, a specificity of 85.71%, a positive predictive value of 98.59% and a negative predictive value of 75%. The PC/SC ratio demonstrated a sensitivity of 81.48%, a specificity of 57.14%, a positive predictive value of 93.61% and a negative predictive value of 28.57%.

Conclusion:

The pleural cholesterol dosage level and the pleural/serum cholesterol ratio can be utilized as unique biomarkers to identify an exudative effusion and replace Light’s criteria.

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.

Pleural, peritoneal and pericardial effusions - a biochemical approach

The pathological accumulation of serous fluids in the pleural, peritoneal and pericardial space occurs in a variety of conditions. Since patient management depends on right and timely diagnosis, biochemical analysis of extravascular body fluids is considered a valuable tool in the patient management process. The biochemical evaluation of serous fluids includes the determination of gross appearance, differentiation of transudative from exudative effusions and additional specific biochemical testing to assess the effusion etiology. This article summarized data from the most relevant literature concerning practice with special emphasis on usefulness of biochemical tests used for the investigation of pleural, peritoneal and pericardial effusions. Additionally, preanalytical issues concerning serous fluid analysis were addressed and recommendations concerning acceptable analytical practice in serous fluid analysis were presented.

Determination of total proteins and lactate dehydrogenase for the diagnosis of pleural transudates and exudates: redefining the classical criterion with a new statistical approach

OBJECTIVE

To propose a new classification criterion for the differentiation between pleural exudates and transudates-quantifying total proteins in pleural fluid (TP-PF) and lactate dehydrogenase in pleural fluid (LDH-PF) exclusively-as well as to compare this new criterion with the classical criterion in terms of diagnostic yield.

METHODS

This was an observational, cross-sectional study with a within-subject design, comprising 181 patients with pleural effusion treated at two university hospitals in the state of Rio de Janeiro, Brazil, between 2003 and 2006. The diagnostic parameters included in the classical criterion were identified, as were those included in the new criterion.

RESULTS

Of the 181 patients, 152 and 29 were diagnosed with pleural exudates and pleural transudates, respectively. For the classical criterion, the sensitivity, specificity, and accuracy for the diagnosis of pleural exudates were, respectively, 99.8%, 68.6%, and 94.5%, whereas the corresponding values for the diagnosis of pleural transudates were 76.1%, 90.1%, and 87.6%. For the new criterion (cut-off points set at 3.4 g/dL for TP-PF and 328.0 U/L for LDH-PF), the sensitivity, specificity, and accuracy for the diagnosis of exudates were, respectively, 99.4%, 72.6%, and 99.2%, whereas the corresponding values for the diagnosis of transudates were 98.5%, 83.4%, and 90.0%. The accuracy of the new criterion for the diagnosis of pleural exudates was significantly greater than was that of the classical criterion (p = 0.0022).

CONCLUSIONS

The diagnostic yield was comparable between the two criteria studied. Therefore, the new classification criterion can be used in daily practice.

Diagnosis and management of malignant pleural effusions

Malignant pleural effusions (MPEs) complicate the clinical course of patients with a broad array of malignancies, which are most often due to lymphomas or carcinomas of the breast, lung, gastrointestinal tract or ovaries. Patients may present with a MPE as the initial manifestation of a cancer or develop an effusion during the advanced phases of a known malignancy. In either circumstance, the median survival after presentation with a MPE is 4 months. Effusions may result from direct pleural invasion (MPE) or indirect effects (paraneoplastic effusions), such as impairment of fluid efflux from the pleural space by lymphatic obstruction or pleural effects of cancer radiation or drug therapy. Because only 50% of patients with cancer who develop a pleural effusion during their clinical course have a MPE, careful evaluation of the effusion to establish its aetiology is required to direct therapy. Management is palliative with interventions directed towards decreasing the volume of intrapleural fluid and the severity of associated symptoms.

Recent advances in the diagnosis and management of malignant pleural effusions

Malignant pleural effusions (MPEs) are an important complication for patients with intrathoracic and extrathoracic malignancies. Median survival after diagnosis of an MPE is 4 months. Patients can present with an MPE as a complication of far-advanced cancer or as the initial manifestation of an underlying malignancy. Common cancer types causing MPEs include lymphomas, mesotheliomas, and carcinomas of the breast, lung, gastrointestinal tract, and ovaries. However, almost all tumor types have been reported to cause MPEs. New imaging modalities assist the evaluation of patients with a suspected MPE; however, positive cytologic or tissue confirmation of malignant cells is necessary to establish a diagnosis. Even in the presence of known malignancy, up to 50% of pleural effusions are benign, underscoring the importance of a firm diagnosis to guide therapy. Rapidly evolving interventional and histopathologic techniques have improved the diagnostic yield of standard cytology and biopsy. Management of an MPE remains palliative; it is critical that the appropriate management approach is chosen on the basis of available expertise and the patient's clinical status. This review summarizes the pathogenesis, diagnosis, and management of MPE. Studies in the English language were identified by searching the MEDLINE database (1980-2007) using the search terms pleura, pleural, malignant, pleurodesis, and thoracoscopy.

Differentiating transudative from exudative pleural effusion: should we measure effusion cholesterol dehydrogenase?

INTRODUCTION

Pleural effusions are often classified into transudates and exudates based on Light's criteria. In this study, the diagnostic properties of Light's criteria were compared to those of several other analytes for the classification of pleural fluids into transudative and exudative.

METHODS

A total of 471 patients with pleural effusions were evaluated. In pleural effusions and simultaneously drawn blood samples, lactate dehydrogenase (LDH), total protein, albumin, cholesterol, amylase, glucose, pH and the cell number were measured. Retrospectively, the clinical records were used to establish a clinical diagnosis. The diagnostic properties of the biochemical tests were calculated using the clinical diagnoses as gold standard.

RESULTS

By clinical diagnosis, 108 patients had transudative and 300 patients had exudative pleural effusions. In addition to pleural LDH activity (accuracy 89%, sensitivity 86%, specificity 97%) and fluid to serum LDH ratio (accuracy 89%, sensitivity 91%, specificity 85%), pleural cholesterol concentration readily identified exudates (accuracy 82%, sensitivity 76%, specificity 98%). Combination of these three parameters achieved a higher overall accuracy (accuracy 95%, sensitivity 93%, specificity 100%) than the Light's criteria (accuracy 93%, sensitivity 100%, specificity 73%). Combination of effusion cholesterol concentration and effusion LDH activity had the highest discriminatory potential (accuracy 98%, sensitivity 98%, specificity 95%).

CONCLUSIONS

Including effusion cholesterol, concentration in the routine biochemical work-up of pleural fluid allows for correct classification of more pleural effusions than achieved by use of Light's criteria. Combination of cholesterol and LDH had the highest discriminatory potential and the added advantage that no patient plasma is needed for correct classification.

Bayesian analysis using continuous likelihood ratios for identifying pleural exudates

STUDY OBJECTIVES

To ascertain if equations that calculate continuous likelihood ratios (CLRs) for pleural exudates improve pleural fluid categorization, especially when false positive or false negative test results are obtained by using Light's criteria.

DESIGN AND SETTING

Retrospective review of the clinical and pleural fluid data from a consecutive series of patients with pleural effusion who underwent thoracentesis at the University Hospital Arnau de Vilanova (Lleida, Spain) over an 11-year period.

PATIENTS AND METHODS

A total of 1490 patients with pleural effusion (298 transudates and 1192 exudates) were recruited into the study. The presence of a transudate or exudate was established by clinical judgment. We examined the comparative diagnostic accuracy of 4 tests (i.e. pleural fluid protein and lactate dehydrogenase (LDH), and pleural fluid to serum protein and LDH ratios) for discriminating between transudates and exudates. Decision thresholds were determined by receiver operating characteristics (ROC) analysis. Equations for calculating CLRs derived from a logistic regression analysis based on a previously described method.

RESULTS

Individual pleural fluid tests did not differ in their diagnostic accuracies according to ROC analysis. We calculated CLRs for the elements of Light's criteria and pleural fluid protein, and also illustrated the sequential use of CLRs for determining posttest probabilities. Overall, CLR formulas had marginal performance for the correct categorization of pleural fluid.

CONCLUSIONS

CLRs provide a probabilistic statement as to the likelihood an effusion is a transudate or exudate. However, clinical judgment is little changed by the application of CLRs, and in doubtful cases a great amount of uncertainty remains. This Bayesian approach is likely to have no major impact on the clinical practice.

Discriminating Between Transudates and Exudates

The dichotomous classification of pleural fluid as a transudate or an exudate simplifies diagnostic efforts in determining the cause of pleural effusions. Multiple pleural fluid tests are available to discriminate between these two classes of effusions. Tests commonly used in clinical practice depend on the detection in pleural fluid of large-molecular-weight chemicals that enter the pleural space to greater degrees in conditions associated with exudative compared with transudative effusions. Considerable misclassifications can occur with all available testing strategies, so clinicians benefit from adopting a nondichotomous, bayesian approach for interpreting test results.

Pleural Fluid Parameters Identifying Complicated Parapneumonic Effusions

BACKGROUND

Controversy exists regarding the clinical utility of pleural fluid parameters as prognosticators of complicated parapneumonic effusions that require drainage.

OBJECTIVES

The purpose of this prospective study is to further assess the utility of these parameters in the management of a larger series of parapneumonic effusions and to determine appropriate binary decision thresholds.

METHODS

We studied 238 consecutive patients with parapneumonic effusions who underwent diagnostic thoracentesis.

RESULTS

We found that pleural fluid pH had the highest diagnostic accuracy (area under the curve, AUC: 0.928; 95% confidence interval, CI: 0.894-0.963) compared with pleural fluid glucose (AUC: 0.835; 95% CI: 0.773-0.897), LDH (AUC: 0.824; 95% CI: 0.761-0.887) or pleural fluid volume (AUC: 0.706; 95% CI: 0.634-0.777). The optimal binary decision threshold for pleural fluid pH identifying complicated effusions requiring drainage was 7.15. Binary, multilevel and continuous likelihood ratios (LRs) for pH were calculated to estimate the likelihood of complication of the pleural effusion. Values for the LRs were compared for each of the three strategies, and relative clinical and statistical significances were assessed. Binary LRs provided significantly less information than continuous strategies.

CONCLUSION

The pH has the highest diagnostic accuracy for identifying complicated parapneumonic pleural effusions. The binary decision threshold determining the need for chest drainage is 7.15 in our patient series. We recommend continuous LRs to estimate the post-test probability of the complication as they provide the most information compared with binary LRs. Our results do not support the use of pleural fluid LDH as independent predictor of complicated parapneumonic effusions.

The use of probrain natriuretic peptide in pleural fluid for the diagnosis of pleural effusions resulting from heart failure

PURPOSE OF REVIEW

Natriuretic peptides are secreted by the myocardium in response to mechanical stretch and have been proposed as a possible test for assisting the diagnosis of heart failure. This article reviews the rationale for measuring N terminal probrain natriuretic peptide in pleural fluid to identify heart failure as the cause of a pleural effusion.

RECENT FINDINGS

Rapid and accurate testing of natriuretic peptides as biomarkers for heart failure is now a clinical reality. In patients presenting with dyspnea, heart failure is usually absent at blood brain natriuretic peptide levels less than 100 pg/mL, possible from 100 to 500 pg/mL, and probable at levels greater than 500 pg/mL. In evaluating natriuretic peptide assays, one needs to consider carefully laboratory and biologic variation, including gender, sex, obesity, renal function, and the assay used. Potential future applications of natriuretic peptide testing include the differential diagnosis of pleural effusion. A recent study has shown good diagnostic characteristics in cardiac pleural effusions, with likelihood ratios of 13 and a diagnostic accuracy of more than 90% for pleural fluid N terminal probrain natriuretic peptide levels > or =1500 pg/mL. Specifically, N terminal probrain natriuretic peptide pleural levels correctly categorized most cardiac effusions misclassified as exudates by standard criteria, and discriminated between cardiac and hepatic transudates.

SUMMARY

Pleural fluid N terminal probrain natriuretic peptide may help accurately differentiate cardiac from noncardiac conditions in patients presenting with pleural effusion.

Biochemical analysis of pleural, peritoneal and pericardial effusions

Body fluids other than blood, urine and cerebrospinal fluid are often submitted for biochemical analysis. Of these, pleural, peritoneal and pericardial fluids are the most common. Laboratory tests are a useful tool to assess the aetiology, pathophysiology and subsequent treatment of effusions. A wide range of biochemical tests may be requested. This review critically examines the various analytes that have been used to investigate these body fluids.

The separation of transudates and exudates with particular reference to the protein gradient

PURPOSE OF REVIEW

The separation of pleural transudates from exudates, as the first step in the study of pleural effusions of unknown cause, is generally accepted as a useful practice. However, the optimal way to do this remains moot.

RECENT FINDINGS

New and more sophisticated biochemical markers have been proposed together, with new approaches to the interpretation of the results. Nevertheless, new studies have consolidated the criteria of Light et al. as those with a better accuracy. Effective diuresis increases the concentration of most pleural biochemical parameters used to differentiate transudates from exudates and appears as the main cause of the failures of this dichotomic approach. Among the alternative criteria proposed for identifying transudates in the setting of diuresis, the total protein gradient between serum and pleural fluid seems to be the most cost effective.

SUMMARY

Together with clinical judgment, the use of biochemical criteria seems mandatory. The criteria of Light et al. remain those of election. In the setting of effective diuresis, the use of the protein gradient is recommended. Although new and more sophisticated markers have been tested, it seems that looking for the causes of misclassification, when applying the criteria that to date have shown better efficiency, deserves preferential investigation.