Do we measure pleural fluid pH correctly?

Diagnostic value of soluble biomarkers for parapneumonic pleural effusion

Parapneumonic pleural effusion (PPE) is a common complication in patients with pneumonia. Timely and accurate diagnosis of PPE is of great value for its management. Measurement of biomarkers in circulating and pleural fluid have the advantages of easy accessibility, short turn-around time, objectiveness and low cost and thus have utility for PPE diagnosis and stratification. To date, many biomarkers have been reported to be of value for the management of PPE. Here, we review the values of pleural fluid and circulating biomarkers for the diagnosis and stratification PPE. The biomarkers discussed are C-reactive protein, procalcitonin, presepsin, soluble triggering receptor expressed on myeloid cells 1, lipopolysaccharide-binding protein, inflammatory markers, serum amyloid A, soluble urokinase plasminogen activator receptor, matrix metalloproteinases, pentraxin-3 and cell-free DNA. We found that none of the available biomarkers has adequate performance for diagnosing and stratifying PPE. Therefore, further work is needed to identify and validate novel biomarkers, and their combinations, for the management of PPE.

Integration of voltammetric analysis, protein electrophoresis and pH measurement for diagnosis of pleural effusions: a non-conventional diagnostic approach

Pleural effusion is very common, but an etiologic diagnosis is often difficult. We used three unconventional diagnostic techniques (voltammetric analysis, protein electrophoresis and pH measurement) performed on pleural effusion to do a preliminary distinction between a neoplastic and a non-neoplastic origin. Pleural fluid samples were collected through thoracentesis, thoracoscopy, or post-surgery pleural drainage of 116 patients admitted to acute care wards. Samples were analyzed with the three unconventional techniques: voltammetric analysis using the BIONOTE system, capillary electrophoresis and pH measurement using a potentiometric method. The BIONOTE system is an innovative system that performs a cyclic voltammetric analysis of a biological liquid sample. The final output of the electrochemical analysis is an electrical pattern that represents a fingerprint of the analyzed sample and each sample has a different fingerprint. Data from the three unconventional diagnostic techniques were analyzed using partial least squares discriminant analysis to discriminate neoplastic from non-neoplastic effusions; we also evaluated sensitivity, specificity and percentage of correct classification. The mean age was 68 years (SD: 12); 78 (67.24%) participants were men. Results obtained from all the unconventional techniques employed showed that neoplastic and non-neoplastic pleural effusions were correctly classified in 80.2% of cases, with a sensitivity of 77% and specificity of 83%. The combined use of voltammetric analysis, protein electrophoresis and pH measurement of pleural fluid can easily and quickly distinguish a neoplastic from a non-neoplastic pleural effusion with reliable accuracy and represents an innovative diagnostic approach. In fact, this protocol can be executed in just few minutes directly in the patient's bed and it holds great promise to improve the prognosis and therapeutic chances.

Pleural fluid glucose testing using a finger stick glucometer: a novel bedside test

Background

Pleural fluid glucose (PFG) has diagnostic and therapeutic implications for the management of pleural effusion. The literature examining point-of-care testing of PFG is limited, and no studies exist for the bedside measurement of PFG using a glucometer (B-PFG). In this study, we compared the accuracy of B-PFG measurement to standard in-lab measurement (Lab-PFG).

Methods

Patients undergoing thoracentesis or thoracostomy were enrolled. PFG was measured at the bedside with a finger stick blood glucometer (ACCU-CHEK^® Inform II, Roche) and in the laboratory. Two consecutive measurements were taken using the glucometer, and their mean was compared to the glucose concentration measured in the laboratory. Pearson correlation coefficient and Bland-Altman Plot analysis were used to compare the two measurements.

Results

Sixty patients were included. Mean age was 64.1 years. Forty-nine patients had exudative effusions (41% malignant, 26% parapneumonic, and 33% others). There was a significant correlation between the B-PFG and the Lab-PFG (r=0.98, 95% CI of 0.97 to 0.99; P<0.0001). There was good agreement between the B-PFG and the Lab-PFG with a mean difference of 14.8 mg/dL [95% limit of agreement (LOA) of -2.2 to 31.8 mg/dL]. This agreement was even better at glucose values less than 80 mg/dL.

Conclusions

PFG measured at the bedside with a glucometer closely correlates with the laboratory measurement. Further studies are needed prior to incorporating this test in clinical practice.

Comparison of analytical performance of i-Smart 300 and pHOx ultra for the accurate determination of pleural fluid pH

Background

Pleural fluid pH is an essential test for diagnosing complicated parapneumonic effusion. We evaluated the performance of two blood gas analyzers in measuring pleural fluid pH.

Methods

The i-STAT G3+ (Abbott) was used as a reference analyzer to evaluate the pH values obtained from other methods: the i-Smart 300 (i-SENS), the pHOx Ultra (Nova Biomedical), using a clot catcher to filter off microclot, and pH indicator paper. Within-device precision was performed using quality control materials. We compared pleural fluid pH (n = 86) by the above methods and analyzed the concordance rate at the level of the medical decision point, pH 7.2.

Results

The within-device coefficient of variations of pH were below 0.1% for all blood gas analyzers tested. The slopes of the regression equations for the i-Smart 300, pHOx Ultra, and pH indicator paper against the reference analyzer were 0.850 (95% confidence interval, CI, 0.800–0.896), 0.714 (95% CI, 0.671–0.766), and 1.105 (95% CI, 0.781–1.581), respectively. The kappa values for the i-Smart 300, pHOx Ultra, and pH indicator paper against the reference analyzer were 0.883 (95% CI, 0.656–1.110), 0.739 (95% CI, 0.393–1.084), and 0.464 (95% CI, 0.102–0.826), respectively.

Conclusions

The i-Smart 300 and pHOx Ultra demonstrated good analytical performance and diagnostic accuracy when determining pleural fluid pH compared with that by the i-STAT G3+, whereas the pH indicator paper showed unsatisfactory results.

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Pleural fluid pH should be determined by a blood gas analyzer using anaerobically collected blood in a heparinized syringe.

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Both i-Smart 300 and pHOx Ultra blood gas analyzers showed acceptable performance for the determination of pleural fluid pH.

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Use of a Clot Catcher prevented instrument errors when testing pleural fluid pH on both blood gas analyzers.

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.