Analytical performance of three point of care methods for pleural fluid pH analysis

Body Fluid Testing at John F. Kennedy Medical Center in Liberia

OBJECTIVES

To apply a simple method to validate testing for albumin, glucose, lactate dehydrogenase (LDH) and total protein (TP) in peritoneal, pleural, and cerebrospinal fluids (CSF) at a hospital in Liberia.

METHODS

Serum and body fluid specimens were mixed to create 100% serum and 25%, 50%, 75%, and 100% fluid tubes, which were tested on a Biotecnica BT3500. Differences less than 10% between calculated and measured concentrations were considered acceptable.

RESULTS

The means (confidence intervals) of the percent differences were: albumin/peritoneal 12.8 (6.0-19.7), albumin/pleural 2.8 (1.3-4.2), albumin/CSF 4.8 (2.2-7.5), glucose/peritoneal 4.0 (1.9-6.0), glucose/pleural 4.4 (3.1-5.7), glucose/CSF 2.9 (1.8-4.0), LDH/peritoneal 9.5 (6.3-12.7), LDH/pleural 9.5 (5.4-13.6), LDH/CSF 9.2 (5.2-13.3), TP/peritoneal 7.6 (3.8-11.4), TP/pleural 3.8 (1.5-6.2), and TP/CSF 4.5 (1.0-8.1).

CONCLUSIONS

All mean differences except for one were less than 10%, allowing for the adoption of clinical testing. The mixing study is a low-cost method for quality-assured testing that can be performed by resource-limited laboratories.

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.