Diagnostic value of Light's criteria and albumin gradient in classifying the pathophysiology of pleural effusion formation in cats

New strategies to classify canine pleural effusions and the diagnostic value of acute phase proteins, amylase, and adenosine deaminase in pleural exudates

BACKGROUND

In dogs, simplified Light's criteria can discriminate transudates from exudates. Other tests used in human medicine are pleural effusion cholesterol (CHOLPE) and butyrylcholinesterase [BChEPE], the pleural effusion/serum ratio of these analytes (CHOLratio and BChEratio), and the serum albumin minus pleural effusion albumin gradient (SEAG).

OBJECTIVES

We aimed to assess the diagnostic accuracies of different biomarkers in dogs with pleural effusion in differentiating exudates from transudates. Secondarily, we evaluated the potential diagnostic utility of pleural effusion acute phase proteins, amylase, and adenosine deaminase in discriminating causes of exudative effusions.

METHODS

Cross-sectional study including 68 client-owned dogs with pleural effusion.

RESULTS

There were 48 exudates (10 septic, 16 neoplastic, 9 hemorrhagic, and 13 classified as other exudates) and 20 transudates. All the variables analyzed, except SEAG, were significantly different between exudates and transudates. Using the cut-off values adopted in human literature, accuracies for CHOLPE, CHOLratio, BChEPE, and BChEratio were between 82.35% and 85.29%; all values were significantly lower compared with the previously published simplified Light's criteria accuracy (i.e., 98%, p < .001 for all comparisons). We found the accuracy of the simplified Light's criteria to be similar to what has been previously reported (95.59%, p = .238). Paraoxonase-1 (PON-1PE) activity and the pleural effusion/serum paraoxonase-1 ratio (PON-1ratio) were significantly lower in exudative neoplastic effusions than in exudative hemorrhagic (p = .004 and p = .001) and septic (p = .004 and p < .001) effusions.

CONCLUSION

Simplified Light's criteria were the best method for discriminating transudates from exudates, and a low PON-1PE activity and PON-1ratio in exudative effusions may suggest an underlying neoplasia.

Simplified Light's Criteria and Acute Phase Proteins Reflect Aetiology of Feline Body Cavity Effusions Better than the Traditional Classification Scheme

The traditional veterinary classification (TVC) of effusions based on cell count and total protein (TP) does not adequately reflect the aetiology. Light's criteria (LC) (activity of lactate dehydrogenase [LDH] in the effusion [LDHef], effusion/serum LDH ratio [LDHr], effusion/serum TP ratio [TPr]), serum-effusion albumin gradient (ALBg), acute phase proteins (APPs) [serum amyloid A (SAA), α₁-acid glycoprotein (AGP), haptoglobin] might aid classification. The aim was to evaluate the utility of these parameters except LDHr in differentiating exudates from transudates. Sixty-five cats with effusions (33 peritoneal, 31 pleural, 1 pericardial), with 18 transudates and 47 exudates based on aetiological classification (AC), were included. The sensitivity, specificity and accuracy of several parameters to identify exudates (based on AC) was assessed. APPs were compared between exudates and transudates based on AC and TVC, with receiver operating characteristics analysis identifying the best APP to recognise exudates. Simplified LC (LDHef, TPr) had an accuracy of 79% and TVC of 48%. ALBg had the highest sensitivity (98%) and LDHef the highest specificity (83%) in identifying exudates in cats. All APPs but effusion SAA could differentiate exudates from transudates based on AC (effusion AGP had the largest area under the curve 0.79) but not TVC. All parameters were better than TVC in identifying exudates. The conformity of APPs with AC but not TVC favours the use of AC to classify effusions.

Value of ultrasonography in determining the nature of pleural effusion: Analysis of 582 cases

To explore the value of ultrasonography in the auxiliary diagnosis of pleural effusion, we retrospectively analyzed the ultrasonographic findings of 275 exudates and 307 transudates and summarized the ultrasonographic image features of pleural effusion according to patients' primary diseases. The findings of thoracic ultrasonography performed before the initial thoracentesis in 582 patients with subsequently confirmed exudative/transudative pleural effusion were analyzed with regard to the sonographic features of pleural effusion. In 275 cases with exudates, thoracic ultrasonography showed a complex septate appearance in 19 cases (6.9%), complex nonseptate appearance in 100 cases (36.4%), complex homogenous sign in 46 cases (16.7%), and pleural thickness > 3 mm in 105 cases. In contrast, in 307 patients with transudates, most patients (97.1%) had bilateral pleural effusion. Ultrasonographic images displayed anechoic appearance and absence of pleural thickening in a vast majority of cases (306, 99.7%; 301, 98%). These positive findings in the exudate were statistically higher than those in their counterparts (P < .05). In the empyema subgroup, the proportion of complex septate appearance, complex nonseptate appearance, complex homogenous sign, and pleural thickening was the highest, at 19/41, 12/41, 10/41, and 30/41, respectively. Ultrasonography is valuable in defining the nature of pleural effusion. Some sonographic features of pleural effusion, such as echogenicity, septation, and pleural thickening, may indicate a high risk of exudative pleural effusion.

Reduced risk of arterial thromboembolism in cats with pleural effusion due to congestive heart failure

OBJECTIVES

The aim of the study was to determine whether cardiogenic pleural effusion in cats is associated with a lower risk of arterial thromboembolism (ATE) compared with cats with cardiac disease without evidence of pleural effusion.

METHODS

A cross-sectional study was conducted on owned cats with natural occurring cardiac diseases. Cats included were classified in three groups: those with cardiac disease but no evidence of congestive heart failure (CHF); those with evidence of cardiogenic pulmonary oedema; and those with evidence of cardiogenic pleural effusion. Prevalence of ATE was calculated and the variables analysed for an association with this outcome were the presence and type of CHF, sex and neuter status, age, breed, type of cardiac diseases and left atrial (LA) dimension. A multivariable logistic regression model was used to fit the association between ATE and these variables.

RESULTS

A total of 366 cats with cardiac disease met the inclusion criteria: 179 were included in the group with cardiac disease but no evidence of CHF, 66 in the group with evidence of cardiogenic pulmonary oedema and 121 in the group with evidence of cardiogenic pleural effusion. Prevalence of ATE (58/366 [15.8%]) was significantly different among groups (with no evidence of CHF, 28/179 [15.6%]; with evidence of cardiogenic pulmonary oedema, 22/66 [33.3%]; with evidence of cardiogenic pleural effusion, 8/121 [6.6%]; P <0.001). Cats with ATE had a significantly higher LA to aortic root ratio (2.30 ± 0.46) than those without ATE (2.04 ± 0.46; P <0.001). Multivariable logistic regression analysis indicated that the group with evidence of cardiogenic pleural effusion was associated with a lower risk of developing ATE compared with groups with cardiac disease but no evidence of CHF and with evidence of cardiogenic pulmonary oedema (P = 0.005 and P <0.001, respectively).

CONCLUSIONS AND RELEVANCE

Presence of cardiogenic pleural effusion is associated with a lower risk of developing ATE, while LA enlargement is a risk factor for ATE.

Retrospective analysis of radiographic signs in feline pleural effusions to predict disease aetiology

Background

The objectives of the study were to determine the prevalence of underlying conditions causing pleural effusion in cats and to calculate the positive predictive values, negative predictive values, sensitivity and specificity of radiographic signs to predict aetiology of the pleural fluid.

Methods

Data from 148 cats with pleural effusion and diagnosed with known aetiologies were retrospectively analysed. Sixty one cats had thoracic radiographs evaluated by consensus through pre-defined radiographic signs by two radiologists blinded to the diagnoses.

Results

Congestive heart failure (53.4%) was the most common diagnosis, followed by neoplasia (20.3%), pyothorax (10.8%), idiopathic chylous effusion (5.4%), feline infectious peritonitis (1.4%) and "other" or cats with multiple diagnoses (total 8.8%). Cats with an enlarged cardiac silhouette had a high positive predictive value of congestive heart failure (90%). Mediastinal masses (100%)and pulmonary masses (100%) were highly predictive of neoplastic disease. Pulmonary nodules (50%) were poorly predictive of neoplastic disease. The remainder of the radiographic variables were not informative predictors of underlying disease.

Conclusions

In our sample of cats, congestive heart failure was the most common cause of pleural effusion. Radiographically enlarged cardiac silhouette and presence of a mediastinal mass may be useful predictors of aetiology, however there are limitations to the use of radiography alone as a diagnostic tool.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03218-3.

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!

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.

Discriminating transudates and exudates in dogs with pleural effusion: diagnostic utility of simplified Light's criteria compared with traditional veterinary classification

OBJECTIVES

To determine whether the simplified Light's criteria (ie, pleural effusion lactate dehydrogenase concentration and serum total protein) can identify the pathophysiology of pleural effusion formation in dogs, and to assess whether these criteria were more accurate than the traditional veterinary classification based on pleural effusion total protein (TPp) and nucleated cell count (TNCCp).

METHODS

This is a cross-sectional study including 100 dogs with pleural effusion. The aetiology of effusion was used to classify the pathophysiology of its formation. Parameters measured included the simplified Light's criteria, TPp and TNCCp. The diagnostic utility of the two methods in classifying pleural effusion formation was evaluated.

RESULTS

Seven transudates due to decreased colloid osmotic pressure, 18 transudates due to increased hydrostatic pressure gradient and 75 exudates were included in the study. The simplified Light's criteria misclassified 2 of 75 exudates (98 per cent overall accuracy). The traditional veterinary classification scheme misclassified 31 of 75 exudates and 12 of 18 increased hydrostatic pressure gradient transudates (57 per cent overall accuracy). The frequency of agreement between the simplified Light's criteria and the traditional veterinary classification with the true nature of the pleural effusion was significantly different (P<0.001).

CLINICAL SIGNIFICANCE

The simplified Light's criteria were highly accurate in discriminating exudates from transudates, while TPp and TNCCp had no diagnostic value in doing so.

Computed tomography attenuation value for the characterization of pleural effusions in dogs: A cross-sectional study in 58 dogs

CT attenuation value can help to differentiate exudate from transudate in people. The aim of this cross-sectional study was to assess the utility of CT in characterizing pleural effusions based on attenuation values in a population of dogs having CT and diagnostic thoracentesis within 48 h of each other. The CT attenuation values were determined using four circular, same size, regions of interest (ROIs) placed on the same CT slice with the greatest quantity of fluid. Values of each ROI were recorded and the mean of the four ROIs mean values (mean of the means) was calculated and considered as the CT attenuation value of that patient. The final population included 23 proper inflammatory exudates, 15 chylous effusions, 12 hemorrhagic effusions and 8 transudates. The median of 'mean of the means' values were: exudate 19.22 HU (8.23 to 37.66 HU); chylous effusion 10.26 HU (-0.90 to 15.37); hemorrhagic effusion 31.65 HU (18.10 to 54.97), and transudate 11.20 HU, (-2.52 to 16.59). CT accurately differentiated hemorrhagic from chylous effusion (AUC 1.0, P < 0.0001) and hemorrhagic effusion from transudate (AUC 1.0, P < 0.0001); CT-values allowed good accuracy in distinguishing exudates from transudates [AUC 0.87 (95%, CI: 0.74-1.0; P < 0.0001)]. HU attenuation values did not accurately differentiate between transudates and chylous effusion. A cutoff value of 34.68 HU (sensitivity of 96% and specificity of 95%) discriminated between exudates and hemorrhagic effusions. CT-value <12.15 HU had a sensitivity of 94% and specificity of 78% for identify transudate or chylous effusion.

Pleural lymphocyte-rich transudates in cats

Objectives Non-chylous lymphorrhagic pleural effusions are transudative effusions with a predominance of lymphocytes; however, they do not contain chylomicrons and therefore do not have the classical milky aspect of true chylous effusion. This type of effusion has been anecdotally associated with cardiac diseases in cats, but studies are lacking. The aim of this study was to investigate the association between this type of effusion and the primary disease. Methods In this study, feline non-chylous lymphorrhagic pleural effusions were retrospectively selected from the database of the authors' institutions over a 3 year period. All cases underwent thoracic imaging, including echocardiography. Effusions classified as transudates with a predominance of lymphocytes on cytology were included. Results Thirty-three cases fulfilled the inclusion criteria: 23 (69.7%) had a concurrent cardiac disease, eight (24.2%) cases were associated with the presence of a mediastinal lymphoma or carcinoma or a thoracic mass, one case (3.0%) was a thymoma and one case (3.0%) was a sequela of a pyothorax. Conclusions and relevance Since a clear lymphatic origin of the fluid could not be demonstrated, lymphocyte-rich transudate might be considered a better designation for these kinds of effusions rather than non-chylous lymphorrhagic effusions. Although the number of cases in this preliminary study is low, the presence of a pleural lymphocyte-rich transudate in a cat should prompt the search for cardiac disease or intrathoracic neoplasia.