Evaluation Of Endotoxin And STREM-1 As Markers For The Diagnosis Of Bacterial Pleural Effusions

BACKGROUND:The differential diagnosis of pleural effusions is very complex. Rapid diagnosis of bacterial pleural effusions is crucial since it is responsible for significant morbidity and mortality. Traditional biochemical parameters are non-specific and Gram stain has low sensitivity. Pleural fluid culture, although being specific, is time consuming. These limitations justify the need for novel biomarkers for the rapid diagnosis of bacterial pleural effusions. The aim of this study was to evaluate the use of endotoxin (lipopolysaccharide, LPS) as a novel biomarker of bacterial pleural effusions.METHODS:102 consecutive patients presenting to the Pulmonology Departments of Huadong Hospital and Zhongshan Hospital from August 2010 to December 2010 with de novo pleural effusions and needing thoracentesis were prospectively enrolled in the study. Routine biochemical markers, cell counts with differential white blood cells, cytology, Gram stain and pleural fluid culture were measured.10 ml of the pleural fluid from each patient was centrifuged at 3000 rpm for 10 minutes at 40C. The supernatant was collected and stored at -800C for later determination of LPS level. Out of the 102 patients,24 were excluded either because no diagnosis was reached or they failed to undergo follow-up, leaving 78 patients to be included in the study.RESULTS:(1) The 78 patients were divided into 4 groups:malignant pleural effusions (n=35), tuberculous pleural effusions (n=18), bacterial pleural effusions (n=12, including 6 parapneumonic effusions and 6 empyemas), transudates (n=13, including 11 heart failure with or without hypoalbuminemia,1 ovarian hyperstimulation syndrome and 1 liver cirrhosis). The patients included in the study were 65±16 years of age,62% were male and 38% female. (2) The levels of LPS differed between the four groups studied (p=0.010). LPS levels in bacterial pleural effusions (0.413 [0.292-1.122] EU/mL) were higher than in malignant pleural effusions (0.303 [0.000-0.628] EU/mL) (p=0.005), tuberculous pleural effusions (0.295 [0.141-0.549] EU/mL) (p=0.010) and transudates (0.180 [0.000-0.600] EU/mL) (p=0.005).(3) Linear correlation was noted between pleural fluid LPS levels and several biochemical parameters: pleural fluid LPS and glucose (r=-0.403, p=0.000), pleural fluid LPS and LDH (r= 0.485, p=0.000), pleural fluid LPS and WCC(r= 0.632,p=0.000), and pleural fluid LPS and protein (r= 0.233,p=0.040).(4) Discrimination between pleural effusions of infectious (bacterial and tuberculous pleural effusions) and non-infectious (malignant pleural effusions and transudates) causes:The threshold of different parameters that best discriminate between infectious and non-infectious pleural effusions were pleural fluid LDH≥380U/L, WCC≥1850 cells/mm3, neutrophils≥19% and LPS≥0.315 EU/mL. The area under the respective ROC curves were comparable (p=0.052). AUC generated by the use of WCC had the greatest value (0.75), while that generated by LPS was 0.65. At a cut-off value of 1850 cells/mm3, WCC had a sensitivity of 60% and a specificity of 85%; LPS≥0.315 EU/mL had a sensitivity of 60% and a specificity of 60%.(5) Discrimination between bacterial and tuberculous pleural effusions:The threshold of different parameters were pleural fluid LDH≥849 U/L, WCC≥3168 cells/mm3, neutrophils≥40% and LPS≥0.334 EU/mL. The area under the respective ROC curves were comparable (p=0.115). AUC generated by the use of neutrophils had the greatest value (0.89), while that generated by LPS was 0.78. At a cut-off value of 40%, neutrophils had a sensitivity of 83% and a specificity of 89%; LPS≥0.334 EU/mL had a sensitivity of 75% and a specificity of 61%.(6) Discrimination between bacterial and non-infectious pleural effusions:The threshold of different parameters were pleural fluid LDH≥585U/L, WCC≥3168 cells/mm3, neutrophils≥45% and LPS≥0.334 EU/mL. The area under the respective ROC curves were comparable (p=0.890). AUC generated by the use of LDH had the greatest value (0.82), while that generated by LPS was 0.79. At a cut-off value of 585U/L, LDH had a sensitivity of 83% and a specificity of 79%; LPS> 0.334 EU/mL had a sensitivity of 75% and a specificity of 66%.(7) Discrimination of exudative pleural effusions:In discriminating bacterial pleural effusions from malignant and tuberculous pleural effusions, neutrophils and lymphocytes gave the largest AUC (0.83). LPS gave an AUC of 0.77, with a cut-off point of 0.334 EU/mL corresponding to a sensitivity of 75% and a specificity of 63%. ADA gave the largest AUC (0.96) when it comes to discriminating tuberculous pleural effusions from malignant and bacterial pleural effusions. As for LPS, the AUC was 0.56 and a cut-off of 0.300 EU/mL yielded a sensitivity of 62% and a specificity of 50%. When comparing malignant pleural effusions to bacterial and tuberculous pleural effusions, the largest AUC was observed with CEA (0.95). For this group, LPS had an AUC of 0.62 and a sensitivity of 63% and specificity of 69% at a cut-off value of 0.306 EU/mL.(8) Combination of parameters for the differential diagnosis of pleural effusions: AUCs produced by ROC analysis using a combination of four parameters (LDH, WCC, neutrophils and LPS) for the differential diagnosis of infectious and non-infectious pleural effusions, bacterial and tuberculous pleural effusions and bacterial and non-infectious pleural effusions were 0.74,0.90 and 0.88 respectively. A combination of five parameters (LDH, WCC, neutrophils, LPS and ADA) raised the AUC of the ROC curve for the differential diagnosis of infectious and non-infectious pleural effusions to 0.89.CONCLUSIONS:Although the level of LPS differs in pleural effusions of different entities, its diagnostic accuracy was inferior when compared to classic parameters. A combination of LDH, WCC, neutrophils, LPS, lymphocytes and ADA offered better diagnostic accuracy in the differential diagnosis of infectious and non-infectious pleural effusions. We believe that LPS measurement in pleural fluid will not have a major impact on clinical practice unless used concurrently with traditional parameters. BACKGROUND:Pleural infection (parapneumonic effusion and empyema) or bacterial effusion is a common clinical problem. Its successful treatment depends on rapid diagnosis and early initiation of antibiotics. The measurement of soluble triggering receptor expressed in myeloid cells-1 (sTREM-1) level in pleural effusions has proven to be a valuable diagnostic tool for differentiating bacterial effusions from effusions of other etiologies.OBJECTIVE:To assess the accuracy of pleural fluid sTREM-1 in the diagnosis of bacterial infection by performing a meta-analysis of studies published.METHODS:We searched Web of Knowledge and Medline from 1990 to March 2011 and CNKI from 1994 to March 2011 for studies reporting diagnostic accuracy data regarding the use of sTREM-1 in the diagnosis of bacterial pleural effusions. The Quality Assessment Tool for Diagnostic Accuracy Studies (QUADAS tool) and the Standards for Reporting of Diagnostic Accuracy (STARD) checklist for the reporting of studies of diagnostic accuracy were used for the assessment of the methodological quality of the included studies. Pooled sensitivity and specificity and summary measures of accuracy and Q* (the upper left-most point on the summary receiver-operating characteristic curve) were calculated.RESULTS:7 individual studies were included. All the studies had a QUADAS score>10 and a STARD score≥20. Overall, the sensitivity of sTREM-lwas 78% (95% CI:72%-83%); the specificity was 84%(95% CI:80%-87%); the positive likelihood ratio was 6.0 (95% CI:3.3-10.7); and the negative likelihood ratio was 0.22 (95% CI:0.12-0.40). The area under the SROC curve for sTREM-1 was 0.92. Statistical heterogeneity and inconsistency were found for sensitivity (p= 0.015, x2 = 15.73, I2= 61.9%), specificity (p= 0.000,x2= 29.90, I2= 79.9%), positive LR (p= 0.000, x2= 33.09,12= 81.9%), negative LR (p= 0.008,x2= 17.25, I2= 65.2%), and DOR (p= 0.000,x2= 28.49,I2= 78.9%). A meta-regression analysis performed showed that the QUADAS score (p= 0.3245; RDOR,4.34; 95% CI,0.11 to 164.01), the STARD score (p= 0.3331; RDOR,1.70; 95% CI,0.44 to 6.52), lack of blinding (p= 0.7439; RDOR,0.60; 95% CI,0.01 to 33.80), and whether the studies were prospective or retrospective studies (p= 0.2068; RDOR,7.44; 95% CI,0.18 to 301.17) did not affect the test accuracy. A funnel plot for publication bias suggested a remarkable trend of publication bias.CONCLUSIONS:Our findings suggest that sTREM-1 has a good diagnostic accuracy and may provide a useful adjunctive tool for the diagnosis of bacterial effusions. However, further studies are needed in order to identify any differences in the diagnostic performance of sTREM-1 of parapneumonic effusions and empyemas.