Darci R Block1, Amy M Wockenfus2, Christopher D Koch3, Brad S Karon4. 1. Mayo Clinic, Department of Laboratory Medicine and Pathology, 200 First Street SW, Rochester, MN 55905, USA. Electronic address: block.darci@mayo.edu. 2. Mayo Clinic, Department of Laboratory Medicine and Pathology, 200 First Street SW, Rochester, MN 55905, USA. Electronic address: wockenfus.amy@mayo.edu. 3. Mayo Clinic, Department of Laboratory Medicine and Pathology, 200 First Street SW, Rochester, MN 55905, USA. Electronic address: koch.christopher@mayo.edu. 4. Mayo Clinic, Department of Laboratory Medicine and Pathology, 200 First Street SW, Rochester, MN 55905, USA. Electronic address: karon.bradley@mayo.edu.
Abstract
OBJECTIVE: The performance of three point of care methods for pleural fluid pH analysis was compared to a currently validated blood gas analyzer. DESIGN AND METHODS: An ABL 725 (Radiometer America, Westlake, OH) was used as the reference method to evaluate three cartridge-based assays: ABL 90 FLEX (Radiometer), and i-STAT 1 (Abbott Point of Care, Abbott Park, IL) CG4+ and G3+ cartridges for pleural fluid pH analysis. Pooled residual pleural fluid samples and quality control material were analyzed to determine intra- and inter-assay precision. Method comparison was performed with spiked (n=40) and clinically-ordered (n=10) pleural fluid samples across the analytical measuring range. RESULTS: All methods demonstrated inter-assay CVs<0.1% at pH values of 7.1 and 7.6, and intra-assay CVs<0.3% at pH values of 7.2 and 7.7. Bland-Altman plots demonstrated clinically significant bias between ABL 725 and each cartridge-based method only at pH>7.6. For samples with pH<7.6 mean bias vs. ABL 725 was -0.01 for ABL 90 FLEX and 0.03 for i-STAT 1 CG4+ and G3+ cartridges. Clinical concordance using a decision limit of pH7.2 was 96-98% for the three methods. CONCLUSIONS: Analytical and clinical performance of the three cartridge-based methods was comparable to a validated blood gas analyzer for pleural fluid pH analysis. Cartridge-based pH methods offer the advantage of easier troubleshooting for clots and clogs as they use disposable electrodes. However cartridge-based methods are not currently FDA-approved for pleural fluid samples, such that additional validation would be required for this specimen type.
OBJECTIVE: The performance of three point of care methods for pleural fluid pH analysis was compared to a currently validated blood gas analyzer. DESIGN AND METHODS: An ABL 725 (Radiometer America, Westlake, OH) was used as the reference method to evaluate three cartridge-based assays: ABL 90 FLEX (Radiometer), and i-STAT 1 (Abbott Point of Care, Abbott Park, IL) CG4+ and G3+ cartridges for pleural fluid pH analysis. Pooled residual pleural fluid samples and quality control material were analyzed to determine intra- and inter-assay precision. Method comparison was performed with spiked (n=40) and clinically-ordered (n=10) pleural fluid samples across the analytical measuring range. RESULTS: All methods demonstrated inter-assay CVs<0.1% at pH values of 7.1 and 7.6, and intra-assay CVs<0.3% at pH values of 7.2 and 7.7. Bland-Altman plots demonstrated clinically significant bias between ABL 725 and each cartridge-based method only at pH>7.6. For samples with pH<7.6 mean bias vs. ABL 725 was -0.01 for ABL 90 FLEX and 0.03 for i-STAT 1 CG4+ and G3+ cartridges. Clinical concordance using a decision limit of pH7.2 was 96-98% for the three methods. CONCLUSIONS: Analytical and clinical performance of the three cartridge-based methods was comparable to a validated blood gas analyzer for pleural fluid pH analysis. Cartridge-based pH methods offer the advantage of easier troubleshooting for clots and clogs as they use disposable electrodes. However cartridge-based methods are not currently FDA-approved for pleural fluid samples, such that additional validation would be required for this specimen type.