Bayesian analysis using continuous likelihood ratios for identifying pleural exudates

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!

Diagnostic Accuracy with Total Adenosine Deaminase as a Biomarker for Discriminating Pleural Transudates and Exudates in a Population-Based Cohort Study

Background

An initial step in the evaluation of patients with pleural effusion syndrome (PES) is to determine whether the pleural fluid is a transudate or an exudate.

Objectives

To investigate total adenosine deaminase (ADA) as a biomarker to classify pleural transudates and exudates.

Methods

An assay of total ADA in pleural fluids (P-ADA) was observed using a commercial kit in a population-based cohort study.

Results

157 pleural fluid samples were collected from untreated individuals with PES due to several causes. The cause most prevalent in transudate samples (21%, n = 33/157) was congestive heart failure (79%, 26/33) and that among exudate samples (71%, n = 124/157) was tuberculosis (28.0%, 44/124). There was no significant difference in the proportion of either sex between the transudate and exudate groups. The median values of P-ADA were significantly different (P < 0.0001) between both total exudates (18.4 U/L; IQR, 9.85-41.4) and exudates without pleural tuberculosis (11.0 U/L; IQR, 7.25-19.75) and transudates (6.85; IQR, 2.67-11.26). For exudates, the AUC was 0.820 (95% CI, 0.751-0.877; P < 0.001), with excellent discrimination. The optimum cut-off point in the ROC curve was determined as the level that provided the maximum positive likelihood ratio (PLR; 14.64; 95% CI, 2.11-101.9) and was22.0 U/L. For transudates, the AUC was 0.8245 (95% CI, 0.7470-0.9020; P < 0.0001). Internal validation of the AUC after 1000 resamples was evaluated with a tolerance minor than 2%. The clinical utility was equal to 92% (95% CI, 0.84 to 0.96, P < 0.05).

Conclusions

P-ADA is a useful biomarker for distinguishing pleural exudates from transudates.

The pleural fluid lactate dehydrogenase/adenosine deaminase ratio differentiates between tuberculous and parapneumonic pleural effusions

Background

Although pleural fluid lactate dehydrogenase (LDH) and adenosine deaminase (ADA) levels are often used to distinguish between tuberculous pleural effusion (TPE) and parapneumonic pleural effusion (PPE), this can be challenging as the LDH level may vary from normal to severely increased in PPE and a significantly elevated ADA is frequently measured in both conditions. In this study, we evaluated use of the pleural fluid LDH/ADA ratio as a new parameter to discriminate TPE from PPE.

Methods

A retrospective study was conducted in patients with pathologically-confirmed TPE (n = 72) and PPE (n = 47) to compare pleural fluid LDH and ADA levels and LDH/ADA ratios between the 2 groups. A receiver operating characteristic (ROC) curve was constructed for identifying TPE.

Results

The median pleural fluid LDH and ADA levels and LDH/ADA ratios in the TPE and PPE groups were: 364.5 U/L vs 4037 U/L (P < .001), 33.5 U/L vs 43.3 U/L (P = .249), and 10.88 vs 66.91 (P < .0001), respectively. An area under the ROC curve of 0.9663 was obtained using the LDH/ADA ratio as the indicator for TPE identification, and the sensitivity, specificity, positive likelihood ratio (PLR), and negative likelihood ratio (NLR) were, respectively, 93.62%, 93.06%, 13.48, and 0.068 at a cut-off level of 16.20.

Conclusions

The pleural fluid LDH/ADA ratio, which can be determined from routine biochemical analysis, is highly predictive of TPE at a cut-off level of 16.20. Measurement of this parameter may be helpful for clinicians in distinguishing between TPE and PPE.

Electronic supplementary material

The online version of this article (10.1186/s12890-017-0526-z) contains supplementary material, which is available to authorized users.

Combined ultrasound-guided cutting-needle biopsy and standard pleural biopsy for diagnosis of malignant pleural effusions

Background

The most efficient approach to diagnose malignant pleural effusions (MPEs) is still controversial and uncertain. This study aimed to evaluate the utility of a combined approach using ultrasound (US)-guided cutting-needle biopsy (CNB) and standard pleural biopsy (SPB) for diagnosing MPE.

Methods

Pleural effusions were collected from 172 patients for biochemical and microbiological analyses. US-guided CNB and SPB were performed in the same operation sequentially to obtain specimens for histological analysis.

Results

US-guided CNB and SPB procedures provided adequate material for histological analysis in 90.7 and 93.0% of cases, respectively, while a combination of the 2 techniques was in 96.5% of cases. The sensitivity, specificity, positive-predictive value (PPV), negative-predictive value (NPV) and diagnostic accuracy of US-guided CNB versus SPB were: 51.2 vs 63.4%, 100 vs 100%, 100 vs 100%, 64.9 vs 72.2% and 74.4 vs 81.3%, respectively. When CNB was combined with SPB, the corresponding values were 88.6, 100, 100, 88.6 and 93.9%, respectively. Whereas sensitivity, NPV and diagnostic accuracy were not significantly different between CNB and SPB, the combination of CNB and SPB significantly improved the sensitivity, NPV and diagnostic accuracy versus each technique alone (p < 0.05). Significant pain (eight patients), moderate haemoptysis (two patients) and chest wall haematomas (two patients) were observed following CNB, while syncope (four patients) and a slight pneumothorax (four patients) were observed following SPB.

Conclusions

Use of a combination of US-guided CNB and SPB afforded a high sensitivity to diagnose MPEs, it is a convenient and safe approach.

Electronic supplementary material

The online version of this article (doi:10.1186/s12890-016-0318-x) contains supplementary material, which is available to authorized users.

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.

Standing prone positioning in establishing causality between matched ventilation-perfusion defects and pleural effusion

Ventilation-perfusion scintigraphy is routinely performed in patients with suspected pulmonary thromboembolism. Pleural effusions in such patients are common and can cause matched ventilation-perfusion defects. This is especially true of the posterior projections in the supine patient. Prone positioning has been described as a useful technique to redistribute pleural fluid anteriorly, exposing perfusion in posterior lung fields; however, some patients have a concurrent condition that renders prone positioning difficult. This report discusses a modified technique that allows patients to be imaged in a standing prone position with excellent results.

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.

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.